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1. rj ERW authDenied Default error messages for denied authorisations This array must associate to the keys selectDenied updateD nied insertDenied and deleteDenied cor responding error messages an empty message will silence the error display The messages can be further customised using the post authorisation hook ERW basicRealm If you set up custom authentication this is the basic realm that will be shown to the user in the authentication dialog 55 Chapter 7 Installation and Configuration _ERW_logLevel A number denoting the logging level required It can be ERW_DEBUG ERW_WARNING ERW_INFO or ERW DEBUG The following variables set up defaults for the user preferences They can be recorded in a cookie so each user can have a different setup _ERW_fontSize The font size in points 0 corresponds to medium in CSS language i e the user preferred size ERW numRows The number of rows for fixed with elements This variable is an associative array indexed by a for TEXTAREA elements 1 for main lists s for selection lists in relation editing x for relationship lists and for filesets ERW uploadFrameHeight The number of pixels of the inline frames containing the HTML elements manag ing file uploads for TEXTAREA elements and filesets If it is possible to determine at runtime the correct width and height
2. B 10 Elements xc Hen SNR t aE ae Re ee 10 SIM ERES 10 eniumval 3 eet trece tet ette reexe ta Dee eter erba oec verse dere ao Era 11 Senium 11 SNO uu m 12 Pig RR 12 WS chicos shies EPEE T TAES E ELEM Lo Adr teret 15 Cip PK P 15 I QR 16 HO m 17 3 The User Interface visscssccessasscsctssccicsestocessesssscwacsssasscvocesvensesesecssoosaevectasessesesssessestensssosecete 19 Stateless Editing ierat ehe ee ae resa heed ctacdsseainsbosaserlenstbineaeceadeses 19 Simulating Remote Procedure Calls sss 20 State Discrepancies ssssssssssseeeeeeee nennen eren nennen nenne 20 Sri 21 4 CustomisatiODaco nones io betreten rove e reae EU EEF VERE PE eV Soure EFE LEVER PUER EXE uoa REX EE Ee ve Pea RENE EP EVO 23 User Interface Customisation ccccccccccsecessecsscessecessessesesseecssesseeesacecseessecsseecseensees 24 ERL LIyp s vs ERW Types nonet emiten rere tree ccs 25 Attribute Specifiers c eerie bete rito ern ene Peer tige 27 Custom Elles erre eter tetto tet Qo rero geo ratore state eerta 28 The Type Array iie nennt reni in rec dese cere 29 Customising Labels retener erede rere 29 Ordering Elements eterne ie ne t be 33 Customi
3. CREATE TABLE loan id int NOT NULL PRIMARY KEY idO0 person int NOT NULL idl book int NOT NULL startdate date NOT NULL DEFAULT CURRENT DATE enddate date duration char 1 NOT NULL Chapter 1 Overall System Design i Again the additional primary key id let us distinguish every relationship even in multirelations whereas id0 person and idi book are the images of a relationship through the two legs The remaining columns are attributes If however the cardinality constraints imposed force the multirelation instantiating a relationship type or its transpose to be monodrome or even a function there is a more efficient method a column named id reiationship type other entity type is added to the table reifying an entity type In this case we say that the SOL table reifying the entity type absorbed the SQL table reifying the relationship type or in formally that the entity type absorbed the relationship type Thus for instance if we modified our example and set upper 1 in the definition of the book leg i e each book is on loan to at most one person and moreover we eliminated all attributes from the relationship instead of a support table we would have produced a new col umn id loan personin the table reifying the entity book That is book would have absorbed loan When ERtool reifies an entity relationship schema it first tries to absorb all rela tionship types without attrib
4. And of course you can access the source target entity types of a relationship type and their supertypes For instance SD loan filter array SD loan filter person_0 fname type t SD loan filter person_O lname type t SD loan filter book_l author type t SD loan filter book_1 author label Author s SD loan filter book_1 title type t SD loan filter startdate type d Sp loan filter enddate type d would have the following effect when editing loans you would get a filter allowing to select loans by borrower s first last name book author title and loan start end date On the other hand the filters for selecting the loans of a certain person in its form would be the book title and the loan start end date analogously for a book Filtering on Owners and Groups Must as in the case of labels ERW sets up two virtual relationship types owner_usr and share_grp They behave as having type r1 and you can use them not only in specifiers but also directly as attributes using the type ris As a result the filter will contain a drop down list with available users or groups Hooks Chapter 4 Customisation Filtering Levels The second array controlling filters is D type filterLevel Its first key is a list type as explained in the Section called The Button Hook and its second
5. ing their output is at best difficult Here we suggest a number of checkpoints to troubleshoot problems starting from database reification up to user interface cus tomisations We assume that you have written a valid ERL file you can tell this by running ERtool without options ERtool problems 1 The most common problem with ERtoo1 is that it cannot find the ERL DTD If you did not insert all DTD related files into your SGML XML catalogues you must be sure that al DTD related files are located in the current directory whenever you use ERtoo1 also symbolic links will do the job 2 If Java complains that it is not finding some classes check that the ERt ool Java archive is properly installed that you have Java 1 4 or greater and that you have an XML parser this should be automatically true with version 1 4 PHP problems l Warning The gettext PHP extension has not been loaded This error message in the logs means that your PHP installation does not include the gettext extensions If you want to use localisation you must reconfigure properly PHP SQL problems 1 First of all check that your database does not report any error when fed with the SOL output of ERtoo1 2 If errors are reported check that they are not due to custom default function specified by default attributes Strip all default attributes from your ERL file and try again 3 If errors persist check the same file with at least another DB
6. library in our main example These files should contain translations for all labels display customisation strings enumerative type labels and help text i e content of help attributes respectively The translation files are usually derived from templates produced by ERtoo1 as it happens with templates produced by xgettext Note that gettext offers several utili ties that makes translations much easier automatic compendia comparison of trans lation and template files and so on Other Localisation Variables As already mentioned in the Section called The ERW con php Initialisation File in Chapter 7 you have some configuration variables that let you decide which character to use as decimal point and decimal comma Moreover you can choose between three date formats namely ISO year month day very sensible European day month year sensible and US month day year broken UTF 8 Support Natively ERW runs using ISO 8859 1 This is the standard character encoding for most PHP installation and for several databases However using ISO 8859 1 is a strong limiting factor if you plan to manage data in languages that are not covered by its codepoints ERW supports fully UTF 8 As usual when character encoding problems are involved the mechanism is not so simple The first step to use UTF 8 support is to make PHP UTF 8 aware This requires compiling in PHP the mbstring extension 75 Chapter 11 Loc
7. Now we have the database but we still cannot modify it Assuming that we installed correctly the ERW PHP scripts in a directory served by Apache we create there a directory named defs generate the definition files with ertool defs lt library xmland move the PHP files thus produced to the defs directory These files contain information used by the PHP run time environment to produce the forms that handle the database Finally you must set up a configuration file named ERW conf php that explains to ERW which kind of DBMS you are using the name of the database and so on There is a sample ERW conf orig php file that you can copy and modify You now need a way to access the scripts handling form The ERW scripts include a sample index orig php file that can be used as a start page copying it to 1X Preface index php If you do so accessing with a browser the directory containing the ERW scripts you should see a list of links named as the entities we defined in the ERL file the list is automatically generated for testing purpose only the database administrator should set up a nicer way to access the editing forms Clicking on them will lead you to the editing forms for instance to edit books you will get a list looking like this Vv Book Mozilla Book Algebraische Grundlagen der Informatik by K U Witt Fractional evolution equations in Banach spaces by E G Bajlekova Scattered spaces with respect to s
8. gt gt f 91 105 131 _ New item Modify _Delete Last Name First Name Donation lt 7 300 000 00 Enable filter Clear filter Figure 5 An ERW list where you can choose subscribers Finally in certain cases you may want to edit relationships directly That is you may want to browse with filtering and modify loans by themselves xi Preface xii v Loan Mozilla Loan Nirmala Achuthan D M Gabbay Khaled A Abdel Ghaf Approximation algorithms Radek Adamec Approximation algorithms Ulrich Abel Queueing systems with heavy tails Ulrich Abel Queueing systems with heavy tails Emile H L Aertm Algebraische Grundlagen der Informat 02 05 2001 Ulrich Abel Queues with regular variation 11 03 2002 14 03 2002 Daniel Abbw Jacks The elements of statistical learning 01 03 2002 10 03 2002 Ulrich Abel Queues with regular variation 21 08 1950 Radek Adamec Scattered spaces with respect to spr 01 01 1000 01 01 2000 Hosam M AboElFotoh Impulsive control theory 10 08 1970 Ilan Adler Queueing systems with heavy tails 21 03 2002 03 04 2003 Nirmala Achuthan Error coding for engineers 02 02 2002 02 02 2002 Jan van den He Algebraische Grundlagen der Informat 02 03 2002 03 04 2002 Jonathan Aaronson Geometry of pseudo Finsler submanifo 10 08 2000 11 08 2000 de lt lt lt gt gt gt gt f 115 715 _Newitem Modify Delete Start date End date 05 03 2000 03 03 2
9. type date attr id duration label Type type enum enumref termlen mand true gt leg entref person label Borrowed gt lt leg entref book label Lent to gt lt rel gt lt erl gt There are several interesting features in this example First of all we include the sys tem entity ERWauth which will automatically include the entity and relationship types that are necessary to handle authorisation Then we declare a static enumerative type that is a function from values to labels The database will store the values but the user will be always presented with the labels Finally we declare the entity types we are interested in note that subscriber is declared as being a person Then we declare our only relationship type The two 1eg XML elements tell ERW which entity types must be related Note also that we specify that the default value for the start date of a loan is the first day of the current millennium but should we be certain that our database fully supports the SOL standard we could use say CURRENT DATE It is now time for a little bit of magic assuming there is an empty database named test and that the file above is named 1ibrary xm1 the command ertool sq1 library xmlwill print on standard output the instructions to create your database Usually piping this code in a DBMS client with the right privileges is enough to set up completely the database
10. 0 N 1 N Chapter 8 ERtool d Figure 8 9 1 N 1 N d 9 d Q Joe EF BH b Figure 8 10 0 M 0 M d Q Figure 8 11 1 M 0 M Figure 8 12 0 M 1 M d Q Figure 8 13 1 M 1 M gt Figure 8 14 0 1 0 N 67 Chapter 8 ERtool 68 d Figure 8 15 1 1 0 N H Figure 8 16 0 1 1 N gt Figure 8 17 1 1 1 N d Figure 8 18 0 N 0 1 a Figure 8 19 1 N 0 1 gt Figure 8 20 0 N 1 1 Chapter 8 ERtool d Figure 8 21 1 N 1 1 H Figure 8 22 0 1 0 1 Figure 8 23 1 1 0 1 d Figure 8 24 0 1 1 1 gt a Figure 8 25 1 1 1 1 Notes l http www oasis open org docbook 2 http www research att com sw tools graphviz 3 http www research att com sw tools graphviz 69 Chapter 8 ERtool 70 Chapter 9 Standards and Browser Requirements ERW heavily relies on browser compliance with respect to a number of standards Presently only Mozilla and thus Gecko based browsers such as Netscape 6 or Galeon Konqueror and thus KHTML based browsers such as Safari and MicrosoftA Internet Explorer from version 5 5 up have a sufficiently compliant implementation of these standards to work properly If ERW detects a browser with insufficient capabilities it will warn the user HTML 4 01 ERW use all features of the W3C standard including lesser known elements such as IFRAM
11. 1 owner This field can be set to true or false the default In the first case for ev ery entity of this type there is a user who holds all privileges about the ele ment i e you have element based authorisation moreover each element can be assign to a group and then all users belonging to the group hold all privi leges about the element the amount of privileges however can be controlled see the Section called The Authorisation System in Chapter 5 There are some re strictions on the entity types for which this attribute can be set to true see the Section called Restrictions on Element Based Authorisation in Chapter 5 Reification An entity type is always reified by an SQL table named as the XML attribute id and having as columns the reification of its attributes Note however that because of virtual types the reification of an entity type may in fact create several SQL tables namely those for dynamic enumerative attributes and those for filesets Additional columns may also appear in the reification of an entity type if relationship types have been absorbed into it Note that when you require element based authorisation you are also requiring it for all subtypes For this reason to avoid inconsistencies only certain entity types can have element based authorisation See the Section called Restrictions on Element Based Authorisation in Chapter 5 Name leg A leg of a relationship type in an entity relationship sch
12. Authorisation ERW is designed to work well in complex intranets in which several users access data with different privileges This requires two basic services that is authentication and authorisation By default ERW delegates completely the authentication process to the HTTP server The system administrator should set up directory access accounts and passwords so that PHP can fill its internal variables Custom Authentication If you prefer to set up your own authentication system you have just to set the _ERW_authenticate variable in the main configuration file This variable must be set to the name of a PHP file containing code that will perform authentication usually looking at the content of the _SERVER PHP_AUTH_USER and SERVER PHP AUTH PW The code will run in the same environment of a hook must end with a return statement and must return true or false depending whether the user is authenticated or not A nonauthenticated user will be presented with the typical HTTP basic authorisation dialog you can set the basic realm that will be shown to the user using the configuration variable ERW basicRealm Note You can extend at will the default authorisation related entities contained in auth xml for instance adding a password attribute with ERW type pw to the entity usr For instance assuming that you added a password column to the usr table you can use the following code php
13. Elements erl 10 In this section we list all ERL elements giving in detail their usage and meaning Name erl A whole entity relationship schema Synopsis The er1 element is the top level element of an ERL document It contains the ent rel enumand fset elements Chapter 2 ERL an Entity Relationship Language Attributes id A restricted identifier for the whole schema the definition file carrying global information about the database structure will be named after this attribute title An optional descriptive title for the whole schema enumval enum Name enumval A value label pair of a static enumerative type Synopsis The enumval element describes a value label pair for a static enumerative type The user will always see the label but the database will store the corresponding value Attributes value The value to store in the database label The label to present the user with Name enum A declaration of a static enumerative type Synopsis The enumelement contains a list of enumval elements describing the value label pairs of a static enumerative type Attributes id An XML identifier for this type 11 Chapter 2 ERL an Entity Relationship Language fset attr 12 label A label for this type mainly for documentation purposes type An SQL type for this attribute If not specified it is assumed to be INT size For the types for which it is meaningful the size
14. a big mistake as relations are directed and this can generate a certain amount of confusion think of the relation father of Traditional entity relationship schema instances use relations instead of multire lations however multirelations are very useful in practise as the library exam ple shows and they can be handled in a clear formalised way using suitable mathematical definitions cfr Multirelational Semantics for Extended Entity Relationship Schemata With Applications Proc of ER 2002 Lecture Notes in Computer Science Springer Verlag 2002 The term leg comes from the category theoretic usage of writing this kind of objects called spans with the R symbol in a raised position Chapter 2 ERL an Entity Relationship Language ERL is an XML based language that describes entity relationship schemata enriched with information that is useful in reification and interface construction It is the foun dation over which ERW is built To understand ERL you must also understand how ERtool will reify ERL defined entity relationship schemata A Quick Tour Before giving the reference to ERL elements it is useful to have an informal discus sion of what you can describe in ERL ERL documents are made of an er1 element that can contain ent elements describ ing entity types and re1 elements describing relationship types Additionally the enum element can be used to create static enumerative types attributes of th
15. are searched for by default As a first access method you can change the name of index orig php file to index php it produces a list of links to the pages that allow you to choose and edit elements of the database However you should devise some custom access page that fits your needs The ERW con pnhplnitialisation File All components of the run time environment source initially the file etc ERW conf php and a file named ERW conf php in the current directory These files must contain definitions for a number of parameters they are normal PHP files so you can for instance use conditionals to provide different parameters on different virtual hosts A sample file named ERW conf orig php is provided for your convenience The following variables are defined in the file above note that following the PEAR convention their name always start with _ERW_ ERW erlId This string must match the identifier given to the er1 element see erl ERW dbType The type of the database you are using Any PEAR specifier mysql pgsq1 will do the job ERW dbOptions If this variable is defined it will be passed as second argument to the PEAR DB connect call Currently the only allowed value is true which requires persistent connections to the database if available ERW dbHost The name of host running the database server ERW dbName The name of the database that should be used 53 Chapter 7 I
16. by declaring it as such or using the GLOBALS array that contains the query that it is going to be written It is an associative array with two indices the first index is a entity type identifier and the second one an attribute identifier note that in the case of subtypes more than one entity type could be involved The corresponding value is the quoted value that it is going to be written By this we mean that strings are actually quoted and escaped and should be passed through the ERW unquote function before being examined Note that in almost all non mandatory fields one of the possible values is NULL During the execution of the pre update hook all types in relation with or owned by the current entity type are locked Queries outside this set could give rise to an error However you can use the lock hook to lock additional tables Caution You should not try to change the locks in the pre update hook To main tain integrity it is necessary that the pre update and the update phase are all executed under the same lock Example 4 1 Checking that a title is long enough In our library no book can have a title with less than two characters Thus we set in the custom file of the book entity set the line SD book preUpdate bookPreUpdate php and fill the file bookPreUpdate php with lt php global q if strlen ERW unquote q book title lt 2 return Title too short else return
17. command line This mechanism allows you to print modularly parts of a huge schema for instance using ertool dot usr grp type you can omit the part of the schema handling au 63 Chapter 8 ERtool 64 thorisation On the contrary in a large schema you would include the types you are interested in A useful feature of DOT supported by ERtoo1 is the possibility of associating a URI to a node ERtool associates to each entity type and relationship type the relative page of the automatically generated documentation In other words if everything is set up correctly you can look with a PDF viewer at your schema and clicking on a entity or relationship type you can immediately see all the relevant information If you prefer you can even generate an image say in PNG format and a client side image map that will obtain the same effect in a browser Making this work is a bit tedious because the links are local and thus must be ab solute usually your browser is already running somewhere so we cannot rely on its current directory being the one we need However they are generated relatively to the current directory so when generating a DOT file you must be in the same di rectory where you translated the DocBook documentation to HTML Moreover the name of the directory containing the documentation must be equal to the id attribute of the root er1 element Let us work out completely an example the example works under most
18. each in stance of fileset or dynamic enumerative type These files should be moved in a place accessible to the run time environment 61 Chapter 8 ERtool Checks 62 defs utf 8 As above but instead of using the standard PHP encoding ISO 8859 1 defini tion files will be output in UTF 8 encoding This is essential if you are using the UTF 8 support forms forml form2 Activates the forms back end For each form specified an ERF file a corresponding PHP file coding the form will be produced These files should be moved in a place accessible to the run time environment forms utf 8 As above but instead of using the standard PHP encoding ISO 8859 1 forms will be output in UTF 8 encoding This is essential if you are using the UTF 8 support default forms Outputs default forms embedded and non embedded for all types in the schema Compiling those forms and installing the resulting PHP files would not modify ERW behaviour as they are equivalent to the run time environment generated default form forms doc However you can modify them to produce custom Activates the documentation back end A DocBook 4 1 2 XML file commenting in detail the entity relationship schema and the reification process will be printed on standard output You can then easily convert it to your preferred format dot Activates the DOT language back end The output can be formatted using the dot utilit
19. eire bn HEEL i EH ETE CER i ro LEE 82 IM OGL CE ONS iii creer areren A e Osee mee eerte rte tees ierra beettsee nbi eter 83 Combining Documents ee cnni niei inae ee i e Hen Ee E cia rore engen 84 Collections of Documents sese eene nene errnet en net etre et etes nnis 84 Aggregation With Independent Works sse nne 84 Vani Slaton asses eee ceca te e eb cen eee rc ex sears bait oa s reed rre ed desis rae 85 Termination Future Revisions of This Licence eene enne eene vi Preface ERW is a system for managing complex and possibly large databases using a web browser Its original purpose was content management that is allowing easy main tenance of web site data organised in a database in a heterogeneous environment where little is known about client machines except that they will have a web browser ERW is based on a formal description of the database in a variant of the common entity relationship model more precisely of what it is usually called the extended entity relationship model An XML based language ERL Entity Relationship Language is used to define formally a entity relationship schema that provides a conceptual description of the database From the ERL based description a Java preprocessing tool ERtool reifies the schema that is it transforms the description based on entities and relationships in a set of tables that suitably implement that description Moreover
20. essentially properties of the entity Note however that if you edit a relationship type directly the permission you get are just those given for that type Some care must be taken when you deny global select privileges on a type when you edit a relationship type from an entity form you should have some select privileges for all entities adjacent by means of an editable relation because ERW has to list elements for you to select them Changing Owner 48 If you have update privileges on a whole entity type you can change the owner of its entities If you have update privileges on an entity you can assign a group to the entity Note Unless you have update privileges on the type you cannot give ownership to some one else and you cannot choose a group the owner does not belong to Chapter 5 Authentication and Authorisation The Selection Level Tuning Each list displaying entities whose type has element based authorisation may feature a distinct selection level This level allows to set independently whether the user can see the entities it owns the entities having its primary group or the entities having a group the user belongs to The mechanism is the same used when doing customisations There are three constants ERW SELECTLEVEL USER ERW_SELECTLEVEL_PRIMARY and ERW_SELECTLEVEL_GROUP that represent the three levels available They are bit masks so for instance you can write ERW SELECTLEVEL USER ERW SELECTLEVEL PRIMAR
21. fire in principle several dozens of parallel HTTP connections as not only the main page but also all relevant IFRAMES must be filled Each script in turn includes JavaScript code style sheets and so on To lessen the burden on the HTTP server ERW tries to make cacheable for six hours all URLs that do not contain database dependent data This include most of the JavaScript and CSS material In this way the load is essentially reduced to one URL per IFRAME A possibly pernicious effect is that when you make an upgrade there could be a mix of old and new code all running in the same browser Moreover to make things work you must be sure that clocks are set properly This kind of problems are however easily solved by forcing the reload of the page involved or for example by upgrading during an enough long period of system inactivity 21 Chapter 3 The User Interface 22 Chapter 4 Customisation A serious problem faced by automatic software generation for content management is the existence of two contradictory goals the application should be generated in a completely automatic way to minimise efforts but at the same time should be highly customisable to satisfy the needs of the users Often the solution is adding custom code to an automatically generated skeleton the custom code can then take care of the details of the implementation that would be difficult or impossible to express However even if this approach is ext
22. form directory which is defined by a suitable configuration variable Form Resolution Forms may present the user with information in different order different language different level of authorisation and so on To provide maximum flexibility ERW de fines a form resolution procedure that determines the form that will be actually loaded in a certain circumstance First of all form resolution is based on a key which by default is given by the name of the type of the element the form will be used with Thus the default key for the form of a book is book Once the key is determined ERW tries first to find a form named key current 1ocale php 8 g book it IT php If the form cannot be found ERW will try key current language php e g book it php Finally ERW will try to load key php e g book php this process is very similar to the one used by Apache to load language dependent pages There are two ways to change the default key the form key hook which lets you choose the key using PHP code and the form ERF attribute which sets the form key for an embedded form ERF an Entity Relationship Form Language ERF is an XML based language that is used to describe custom forms Note that there are two kind of forms embedded and non embedded Non embedded forms are the standard ones using them you alter each element of an ERW database Embedded forms on the other hand allow you to edit relationships directly into the form
23. key which is to be specified only if the first key is not main is of the form relationship type other entity type for relationships types and attribute name for filesets It specifies a filter level i e a real number between 0 an 1 inclusive that overrides the default for any of the lists appearing in a form allowing fine grained customisation As an example SD book filterLevel rel loan_person 0 will set up all filters for searching persons who borrowed a book The default filter level can be changed in the default customisation file using the key chain p filterLevel followed by a key giving the type of list as explained in the Section called The Button Hook Thus for instance D filterLevel rel 0 would set all filters for all relationship lists Default Values Sometimes in particular with very large databases you may want to present since the start a list which selects a subrange of items to this purpose ERW allows you to set default values for filters Similarly to default value for attributes you have to specify an SQL expression that will be evaluated to produce the initial filter value The expression must be stored using the key default which is as the same level as type label etc For filters with operators you can also specify the preferred operator using the key operator For instance SD loan filter array SD loan filter startdate type
24. overall subject For example if the Doc ument is in part a textbook of mathematics a Secondary Section may not explain any mathematics The relationship could be a matter of historical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released under this License The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public whose contents can be viewed and edited directly and straightforwardly with generic text editors or for images composed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters A 81 Appendix A GNU Free Documentation License copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent A copy that is not Transparent is calle
25. possess id class and style attributes and an element style with attribute type The element img has also attributes src alt longdesc width and height Finally there is an element a with an additional attribute href but note that for obvious reasons the linked page will be always opened in a new window For the meaning of these elements and attributes please refer to the HTML or XHTML documentation erf Name erf A whole custom form Synopsis The erf element is the top level element of an ERF document It contains any other ERF element Attributes ref The type this form refers to emb A boolean denoting whether this form is embedded or not If not specified it is assumed to be false input Name input An input control Synopsis The input element defines where the input control s for a certain attribute will ap pear in the form Attributes ref The ERL attribute this element refers to 43 Chapter 4 Customisation list 44 label An alternative label for this attribute If not specified the localised version of the label specified in the ERL file will percolate through help Alternative help text for this attribute If not specified the localised version of the help text specified in the ERL file will percolate through type An ERW type If not specified the type specified in custom files will percolate through size For the types for which it is meaningful e g text the
26. procedure call RPC mechanism using a hidden frame this technique is often called remote scripting Every form contains an invisible IFRAME element that is used to interact with the server Whenever the user interface code needs some data from the database for instance because the user is browsing a set of entities the location of the IFRAME ele ment is set to a particular URL that will load into the IFRAME element some JavaScript code in turn this code manipulates via the DOM the user interface shows these data to the user and updates the JavaScript state The effect is much like an RPC State Discrepancies 20 Statelessness has a relevant consequence which users can find disorienting at first the state of the browser is not necessarily synchronised with the content of the database For instance if someone else adds an entity it will not show up in your main or selection lists at least until you re filter their content or move around with arrows Chapter 3 The User Interface Correspondingly it is possible that you deleted say a relationship without breaking any cardinality constraint however since in the mean time another user has deleted other relationships your operation becomes illegal In this case ERW will warn you and show you again the form you were editing this time with updated information about the database content Caching A page with a rich set of features text areas filesets etc can
27. really of a more specific type only if the same id exists in a subtype This can be exploited as follows SD document display fmtString s s 0s s s 0s s SD document display field array title publication id Publication techrep id Technical Report The id field is used to trigger the 0s specifier but because of the limitation on the output 0 the id is not really printed Rather the strings Publication and Technical Report are only printed if the document is a publication ora techrep respectively Local Customisation It can happen that the standard way to label an entity does not work in all situations The typical example is given by weak entities suppose again you have editions for books and that editions are weak entities whose owner is the respective book Cer tainly to label in general an edition you will use also fields from the owner for ex ample title and author by means of attribute specifiers However you will more likely access editions in the context of a specific book us ing a suitable ERW type In this case however you need just to show information about the edition and not information about the owner which is already currently displayed End date Chapter 4 Customisation For this kind of situation ERW offers local customisation For each relationship type you can specify a label for the related entities which will override the s
28. return db gt getOne select COUNT from usr where login ERW quote SERVER PHP AUTH USER and password ERW quote _SERVER PHP_AUTH_PW Put this code in a file named say authenticate php located in the main server di rectory set ERW authenticate to authenticate php in the main configuration file and you re done The Authorisation System The permission system used in ERW follows strictly the UN X conventions and if you are used to those conventions you will find it very natural To enable it you must include the XML entity amp ERWauth in your ERL file This will include the XML file auth xml which generates a few tables that ERW uses to keep track of authorisation information The table definitions can be extended at will for instance providing a password field as long as the relational structure and the provided attributes are left intact If you do not include amp ERWauth everyone can do everything Warning Even if you do not want to use authorisation you cannot use the name type for a type as it is used to detected the presence of the authorisa tion system First of all there are entities types usr and grp with obvious meaning related by belongs and by primary In this way you can set up accounts for each account you must specify a mandatory real name and an optional e mail address and groups 47 Chapter 5 Authentication and Authorisa
29. size of the HTML input control readonly If true this attribute cannot be changed by the user tabindex This attribute is in all ways identical to the corresponding HTML attribute and will be passed to the HTML input control Name list An input list or set of lists Synopsis The 1ist element defines where the list s for a certain relationship or fileset type will appear in the form this includes also transpose of identification functions in which case you are really editing owned weak entities Attributes ref The fileset or relationship type this element refers to label An alternative label for this set of lists s If not specified the localised version of the label specified in the ERL file will percolate through help Alternative help text for this set of list s If not specified the localised version of the help text specified in the ERL file will percolate through Chapter 4 Customisation type An ERW type If not specified the type specified in custom files will percolate through form A form key that will be used in the form resolution process to load the embed ded form for this set of lists s readonly If true this fileset or relationship type cannot be changed by the user tabindex This attribute is in all ways identical to the corresponding HTML attribute and will be passed to the HTML input control 45 Chapter 4 Customisation 46 Chapter 5 Authentication and
30. that let the user scroll to see long labels Moreover the editable attribute of the leg element allows you to select from which side the user can edit relationships 19 Chapter 3 The User Interface Stateless Editing The main ingredient in the design of ERW s web interface is stateless editing HTTP is a stateless protocol and as such is not prone to support stateful interaction with a server this is usually achieved with a mix of cookies and server sessions imposed over the protocol ERW is designed to let the user edit freely a database recording no information server side All state related to the modification made by the user is stored client side so that the connection to the database is truly stateless This approach has a number of advantages in particular it adheres to the principle of least surprise web users are by now accustomed to the idea that closing abruptly a web page or even killing the browser even in the middle of a multi page form submission will result in no changes being recorded server side Indeed any web form is an example of stateless editing input controls store client side the current choice of the user The situation however is completely different when we take into consideration relationship editing The user before submitting any information to the server should be able to add rela tionships delete old or new ones and edit their attributes without storing state on the server This re
31. the same key set Note that for weak entity types the leg of the identifying functions are part of the key see rel hidden This field can be set to true or false the default In the first case the user is never presented with the attribute but the attribute is retrieved and rewritten without change on updates This allows to create fields to store additional infor mation not edited through ERW but maybe computed each time the element is updated Reification An attribute that is not of type enum or fset is reified by an SQL column in the obvi ous way Enumerative types of identifier att ribute name generate a column named attribute name in the case of a static enumerative attribute and the type of the col umn will be given by the static enumerative type whereas they will generate a col umn named id attribute name of SOL type INT in the case of a dynamic enumera tive attribute This column points to a table named entity type attribute namethat contains the actual elements of the type The table can be edited much like an entity table As we mentioned previously attributes of type fset do not generate an SOL column but rather a support table again named entity type attribute name containing the attributes of the fileset if a file set type is present and two additional columns file isa ent Chapter 2 ERL an Entity Relationship Language holding the actual name of a file in the file system and id_belongs_entity typ
32. this case non absorbed relationships can be edited only from the type that is highest in the type hierarchy where highest means appearing later in a breadth first visit of the hi erarchy This has a side effect if the relation is total in the opposite direction you will most probably get errors This configuration however is purely theoretical and indeed it is so contrived that it should never happen in real schemata Attribute Specifiers Customisation requires specifying attributes possibly of related types e g for fil tering displaying ordering etc An attribute specifier lets you access dynamically attributes and relationships of supertypes subtypes and related entities when fil tering labelling or ordering However you must understand completely the pitfalls involved in particular the cases when an attribute specifier may have a NULL value The general form of an attribute specifier is leg codomain relationship type qualifier attribute The formal description above is quite unfathomable However it embodies a simple idea you start from the current type and move along relationship types reaching the type containing the attribute you are interested it At the end you may need to jump to a supertype or a subtype to get the attribute you need this is the r le of qualifier note that jumping to a supertype guarantees the existence of the attribute but jumping to a subtype could lead to a non existing attribute
33. type you should specify here the XML identifier of an enum element fsetref If the type attribute is set to fset and you want the generated fileset to have attributes you should specify here the XML identifier of an set element size For the types for which it is meaningful the size of the attribute For text types it is the maximum number of characters that can be stored and defaults to 255 For numeric types it is the number of meaningful digits scale For numeric types the scale that is the number of fractional digits by default 0 Note that the scale is included in the size so a numeric type with size n and scale s has n s digits to the left of the point and s digits to its right regex A JavaScript regular expression defining the valid content of this attribute This is meaningful only for text and numbers and provides a generic flexible way of checking user inputs The user will be prevented from setting the content of this attribute to a string that does not conform to the regular expression Note that the empty string is always a valid input for a non mandatory attribute Warning The input provided by the user is valid if it matches some where the regular expression if you want to give a tight con straint i e on the whole content you should start your ex pression with and end it with 5 as usual Note that to avoid to confuse the user it is probably a good idea to permit trail ing spaces 1
34. you create a symbolic link to it in your document root and recall it as a URL e g http example com checkERW php or you start it from the command line using php C f ERW checkERW phpin the latter case your current directory must be your document root Note that if you in stalled the ERw directory in a special place you will have to give the complete path for instance php C f usr share php ERW checkERW php Note It may happen that your custom files contain some special code that sets some customisations conditionally Usually this code will not work when run out of context by checkERW php However checkERW php sets a variable named ERW check by testing whether the variable exists you can discover whether you are being run by checkERW php and skip problematic code ERW checkdb php This script is never called during editing It checks the overall database integrity including referential integrity logical integrity correspondence between ERW defini tion files and SOL table definitions and so on For a correct system it should give no message The methods to invoke this script are the same of checKERW php Warning Even for a small database the running time of this script will certainly exceed the default maximum execution time for a script set in the PHP main configuration file This should not be a problem because the script tries to set for itself unlimited execution time However if you set safe mode on in
35. 001 21 12 2002 01 01 2003 03 03 2002 03 04 2002 21 03 2002 21 04 2002 21 03 2002 21 04 2002 First Name Last Name Author s Start date lt 4 Enddae 4 Enablefiter Clear filter Title ES eee SaaS Figure 6 An ERW list where you can choose loans The forms thus generated may not really suit your needs In this case you can try to customise them A simple form of customisation for instance is localisation la bels and user interface elements can be translated in any language and the correct language for the user will be negotiated with the browser However you can also define your own forms using ERF an XHTML like language here we have a simple self explanatory example for a subscriber lt xml version 1 0 gt lt DOCTYPE erf PUBLIC DSI DTD ERF V1 0 EN file erf dtd gt erf ref subscriber gt style type text css fieldset background BOBOBO border solid black legend background 808080 border style lt fieldset gt black solid thin legend style background EQEOEO gt User Data lt legend gt lt input ref person fname size 20 gt lt input ref person lname size 20 gt lt input ref address size 80 gt lt fieldset gt lt fieldset gt lt legend gt Subscription Data lt legend gt lt input ref card size 8 gt lt input ref donation gt lt fiel
36. 2 The Post update Hook The post update hook is called after actually updating the content of a row or in serting a new row It is set by assigning to the variable D type postUpdate the name of a PHP file Note that the file is relative to the server directory where PHP scripts are installed If it exists the file is included you have at your disposal 37 Chapter 4 Customisation 38 the same variables as in the pre update hook Usually at this point some additional update or check of the database is performed Post updates hooks are run initially for embedded entity relationship and fileset types Then the hooks for the element modified or created by the form are executed in the case of supertypes hooks are invoked from the current type upwards i e exactly in the dual way w r t pre update hooks This allows you to impose complex contraints to relationships even belonging to different types as you can check them looking at the current database content during the post update hook After your custom checks and changes you can return nu11 to specify that you are satisfied with the current situation or a string in the latter case the transaction will be aborted and the string will be displayed to the user as an error message much like a pre update hook Warning Transaction support is not currently available using MySQL Returning a non nu11 value will lead to unpredictable results During t
37. 3 Chapter 2 ERL an Entity Relationship Language 14 default A default value for this attribute The allowed content depends on your database although by SQL 99 standard you can use a literal CURRENT_DATE CURRENT_TIME and a few other specifiers in PostgreSQL you can use any variable free SQL expression For example by setting default to CURRENT_DATE for a date the user will be presented with the current date as default value Warning ERW can perform little or no check on the content of this attribute Try to use standard SQL constructs for portability and check carefully the resulting type In particular constant strings must be quoted e g default a string mand This field can be set to true or false the default In the first case the user is required to insert some data for this attribute trim This field is meaningful only for ERL text types and can be set to true the default or false In the first case this attribute will be trimmed More precisely trimming happens following the ERW type associated see the Section called ERL Types vs ERW Types in Chapter 4 for type pw no trimming for type t left and right trimming for type a left trimming key This field can be set to true or false the default The set of fields for which this attribute is true constitutes the key set of the entity or fileset ERW will prevent you from inserting two elements with
38. Calendar installation usually installing J5Calendar in the document root in a directory named jscalendar and setting this variable to 3scalendar is a good choice ERW localePath An absolute path specifying the directory where gettext localisation files are stored If you need to specify a directory relative to the document root of the HTTP server use the PHP variable GLOBALS DOCUMENT_ROOT _ERW_fixedLocale A fixed locale which will override the one provided by the browser Set it to the empty string if you want to use the locale provided by the browser _ERW_defaultLocale A default locale to be used instead of en us when the browser does not provide a locale and no fixed locale has been set ERW decimalPoint The character for the decimal point i e the character that separates the integer and the fractional part of a number Chapter 7 Installation and Configuration ERW decimalComma The character for the decimal comma i e the character that separates triples of digits in the integer part of a number ERW dateFormat A number denoting the date format you prefer It can be ERW DATE ISO ERW DATE EU Or ERW DATE US See also Chapter 11 Warning Do not make on the fly changes to this value changing it should be considered as severe as installing a new version of ERW Browser caching of JavaScript code can cause pernicious inconsistencies see also
39. E LABEL FIELDSET and LEGEND CSS ERW uses CSS1 and some features of CSS2 The W3C Document Object Model ERW access and dynamically updates HTML elements using Level 1 of the W3C Document Object Model specification plus bits of Level 2 mainly for style ECMAScript ECMA 262 ERW uses as a scripting language the standardised version of the JavaScript lan guage originally developed by Netscape 71 Chapter 9 Standards and Browser Requirements 72 Chapter 10 Useful Functions In this chapter we discuss functions defined in the run time environment that also users writing hooks could find useful Database Functions When executing a hook you can access some static functions of the ERW class that can simplify your access to the database Note that all these functions stop the current script and write to the log file in case of an error ERW ERW ERW ERW ERW ERW log file line message level Logs a message if the current logging level is equal to or below the one spec ified in the main configuration file Possible levels are ERW DEBUG ERW INFO ERW WARNING and ERW ERROR the default The first two parameters are usually filled using the PHP macros FiLE and LINE respectively quote string or array Quotes a string for SOL processing Note that when applied to an array of strings it will quote by reference the whole ar
40. ERW The Manual Sebastiano Vigna ERW The Manual by Sebastiano Vigna Copyright 2001 2002 2003 2004 2005 Sebastiano Vigna Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foundation with no Invariant Sections with the Front Cover Texts being ERW The Manual Sebastiano Vigna and with no Back Cover Text A copy of the license is included in the appendix entitled GNU Free Documentation License Table of Contents n f Te MENO T IE vii A Simple EX ADAP les 3 5e atento eee ite s quei esci onct acce redee viii 1 Overall System D esigti iie tote tnra tron eh chscsssssbovanssenssiedssssonsasonsasbiasssssedsbaocossssastabes 1 Entity Relationship Schemata eerte eterni retener eer eee 1 Cardinality Constraints sse entente tenente tenes 3 Weak Entities zat erret aito terree rib ere Navies 5 elder d 5 ReifiCcatiODbiccsiematen dini eren ecd ine der eve vr ERE EVE repere ra Peer ERU ETE 6 COMCUITEN CY D M 7 2 ERL an Entity Relationship Language eese tntntntn tnt tenntntn tnn 9 A Quick Tout 2a cde descendre dame d een e ed aen na ied 9 Types and Identifiers eere eere recte rem reperies 9 lheenumttype eec anmoiseciane aaepe Oe cnt cde e 10 The fset LY Pe ais
41. Identification functions are simply represented by a bold arrow from the weak entity type to the owner the name is not relevant as there can be at most one such function between two entity types 65 Chapter 8 ERtool 66 L J Figure 8 5 An weak entity type and its owner linked by an identification function Relationship Types Relationship types are represented by diamonds containing the type label again no attributes are shown Relationship types that are to be instantiated to multirelations are shown with a thicker border as multirelations are somehow fatter than relations The representation of the remaining cardinality constraints is very simple a cardi nality constraint of the form 1 x adds a black dot at the end of the corresponding leg Thus when you see a black dot you should read mandatory as in Object Role Modelling A cardinality constraint of the form x 1 instead generates an arrow tip near the diamond This corresponds to the mathematical fact explained in detail in the Section called Cardinality Constraints in Chapter 1 that such a constraints makes a leg into a partial function from the entity set to the relationship set Moreover it shows immediately and intuitively that there is just one way to go from the entity set to the relationship set and thus to the other component type sets as legs are functions ES Figure 8 6 0 N 0 N EJ Figure 8 7 1 N 0 N ER Figure 8 8
42. Linux dis tributions Starting with library xm1 we first generate its documentation and the DOT file ertool doc lt library xml gt libraryDoc xml ertool dot library xml gt library dot Then we produce the HTML documentation Note that we set explicitly the output directory to match the id attribute of the root er1 element db2html libraryDoc xml o library Finally assuming GraphViz has been installed successfully we generate a graphical display dot Tps2 library dot gt library ps ps2pdf sPAPERSIZE a0 library ps There are several options of dot that can be used to tweak the output you can even prefer the spring embedder neato but remember to specify the option Goverlap false In the end the resulting PDF file will contain hyperlinks to the HTML documentation that makes it easy to browse the schema ry Loan Mozilla o le Eek yew Go Bookmare Tools Window Help Q O Q Q Eiren c Gs Se 4i Home Bookmarks vi EX A Library Previous Relationship Types Loan Ue Subveer T Table 4 Loan loan see table loan Entity Type Label Cardinality Key Editable Note itu Primary udi I Person persen Bomowed 9M x oe Book book Lentto OM x r Table 5 Attributes of Loan E Uer a Label d Type Size Scale Man
43. MS it can happen that some database does not support the fragment of SQL 99 used by ERW Configuration and Customisation Problems 1 First of all check that both checkERW php and checkdb php do not report any error about your ERW configuration and database content In particular if you upgraded from a version without original filenames a missing column original will be reported in each fileset Please regenerate the SOL code to see how these columns should be created 2 If you have custom files remove them gradually so that you can tell whether the problem is caused by a customisation or by a hook 79 Chapter 13 Troubleshooting When Nothing Seems to Work 1 N ies 4 First of all check that you have the very last version of all components in volved This means a recent version of the DBMS of the HTTP server of PHP of PEAR and of the browser Force your browser to reload all files Even if you have the last version of ERW your browser could be caching old scripts If you can erase the cache alto gether Then check the logs You should have the maximum level of logging enabled in your PHP configuration file including logging of all warnings ie error reporting E ALL and also the ERW logging set to the maximum level ie ERW logLevel ERW DEBUG Warnings about usage of undefined variables usually show that you have misdefined some customisation variables or hooks In this case try first t
44. Y to mean that you want to list entities the user owns or entities whose group is the user s primary group There are variables you can set in the default customisation file using the key chain D selectLevel followed by a key giving the type of list as explained in the Section called The Button Hook in Chapter 4 Thus for instance SD selectLevel list ERW SELECTLEVEL USER sets the default for main entity lists to entity owned by the current user For a finer tuning you can set separately the level for each list The relevant variable is D table selectLevel Its first key is a list type and its second key which is to be specified only if the first key is not main is of the form relationship type other entity typefor relationships types As an example assuming that we required element based authorisation for person and that we did not grant table wise select privileges SD book selectLevel sel loan person ERW SELECTLEVEL USE will force only persons we own to be listed for creating loans Restrictions on Element Based Authorisation Element based authorisation is useful but it can easily lead to inconsistencies For instance if Ais a B and you require element based authorisation for both entity types you could end up with a different owner for the same entity when you see
45. ained in a directory named custom located where the run time envi ronment PHP scripts are You can create a customisation file for each entity type relationship type and instance of fileset type you would like to customise The file Chapter 4 Customisation must be named as the identifier of the type postfixed with php A instance of fileset raising from an attribute A of an entity type T has identifier r_a and then the same rule applies There is also a default customisation file that is used to change defaults throughout all types It is named as the identifier of the root element of your ERL file postfixed with php in our library example it would be named library php Each section on customisation specifies how to change the defaults using this file whenever possible Your custom files are executed in the same environment of a hook thus you can tweak customisation using information such as the name of the user Customisation files however should be light as they are loaded each time a type is used All customisation in custom files is performed by setting certain keys of the array D the first key is always the name of the type that is being customised e g D person The custom files are loaded from higher to lower types and this allows you to customise higher types from the custom file of a lower type This is most useful for instance you could decide to customise an attribute of person in a different way when it app
46. al forms that will actually make a user able to manipulate the server password file 50 Chapter 6 Transaction Support ERW provides partial support for SQL transactions and constraints The support does not work presently for MySQL The usefulness of SQL based constraints is evident if you access your database with different clients in this case including constraints at the SQL level avoids duplicating efforts ERW runs all update and delete operations inside a transaction In case of an SQL error the transaction is rolled back The same happens when a post update hook or a post delete hook returns a non nu11 value However to avoid cluttering the code logic SOL errors cause a log to be written and no further action being taken This usually results in the user seeing an empty form or a form with empty lists The notable exception however is the insertion or update of entities and the com mit phase at the end of an update or delete operation In this case errors lead to pre senting again to the user the form that was submitted displaying the error message coming from the database unfortunately the message coming from the database is often not exactly explicative Thus you can easily add SQL constraints to your database if they are checked during one of the phases above For instance deferred constraints are checked during the commit phase thus they are handled correctly by ERW The endorsed way of writing SOL base
47. al function For simplicity in ERW partial functions are always absorbed into their source if you declare an injective relation that is not a partial function ERtoo1 should absorb it into its target You just have to exchange the two legs Only the first leg can be a key For simplicity in ERW identification functions start from the weak entity type and end on the owner You just have to exchange the two legs The DOT graphical back end There is currently no graphical editing tool for ERL files However there is a graph ical back end outputting parts of a schema in the DOT language The DOT file can then be processed using standard tools from the GraphViz suite of tools which con tains layout generators GUI editors etc To activate the back end you must use the dot option followed by a possibly empty sequence of entity type identifiers each of them can be prefixed with If the sequence is empty the whole schema is output Otherwise if there are just identifiers prefixed with those types are removed from the output In the other cases the set of entity types included in the output is built as follows every identifier without the prefix adds to the output the type itself all its supertypes all the types it owns and all the types adjacent to the previous ones every identifier with the prefix removes the corresponding entity type from the output Each rule is applied following the order of the parameters on the
48. alisation which allows to handle transparently strings in several encodings Unfortunately several distributions do not release PHP with the mbstring extension enabled so you may have to recompile PHP although if you have a decent packaging system this should turn out to be rather easy To check whether your PHP installation has mbstring you can look at the output of php m Once the mbstring extension has been loaded you must enable UTF 8 support by setting the configuration variable _ERW_ut 8 and configure PHP to use UTF 8 by modifying the following parameter in the PHP configuration file mbstring func_overload 7 It is essential that all functions are overloaded with those of mbstring otherwise ERW will stop and log an error message Note that this parameter may be set in the main configuration file only ERW will generate a suitable HTML tag that will inform the browser that its output is encoded as UTF 8 However it is good practise to communicate this information before the page is actually output using an HTTP header this can be obtained setting the following PHP configuration variable default_charset UTF 8 The value of default_charset can also be changed locally using an htaccess file Be sure to have the required permissions AllowOverride Options and just add a line php_value default_charset UTF 8 The rationale behind UTF 8 support is that everything should be in UTF 8 Thus with UTF 8 support act
49. all related entities of m Weakness is recursive If x owns y and y owns z then x indirectly owns z Of course it must never happen that an entity is owned by another one by means of two distinct ownership paths as a special case it must not happen that an entity owns itself ERtool performs a novel static check guaranteeing that this will not happen Subtyping The last concept we need is that of subtype When you say that entity type A is a subtype of B or more informally that A is a B you are saying that all attributes of B are also attributes of A and all relationship types incident to B are also incident on A this phenomenon is usually called subclassing or inheritance in object oriented jargon In our example subscriber is a subtype of person indeed each subscriber has a name but has also other information Chapter 1 Overall System Design ERW supports subtyping For each entity type you can specify using the isa ele ment any number of supertypes whose attributes and incident relationship types will be inherited this is called multiple inheritance in object oriented jargon Obvi ously you cannot form cycles ERtoo1 will prevent you from doing this Semantically subtyping is modelled by set inclusion That is if A is a B then in every schema instance the set associated to A is a subset of the one associated to 8 That is every entity of type A is also an entity of type B To be completely precis
50. and Configuration eese eeeeentntn ttt tn ntn tnensnatntntnus 53 The Run Time Environment eese eene rennen erre eeki Kn ESES enne 53 The ERW con php Initialisation File sse 53 Gloatifeapivie Tidi t 56 Configuring FITMDLJA rea iater treten eerte enirn era Pri eee Pe eee 57 Configuring PCKeditor iere hb detener ec naan S EENE 58 Configuring JSCalendar isisisi eass eiae asas 58 LED EAA EEA EAE R I AT E O SE 61 ODHODS oai ate T d a dead T E 61 Checks oeil eed A s A Pd d 62 Error Messages ences e ciie antes nd kirss ESEESE sissi nb n e d e LA Seer eed 63 The DOT graphical back end 5 irr teet eet trarre seres 63 The ERW Graphical Notation eene 64 Entity Dy POS iiien nri aar i E EE EEEE EE E EERE EEEE 65 Relationship Ty Pes sristi e eaae ke 66 9 Standards and Browser Requirements ssesesseseesessesesreseeseseesesreseoseseoseseeseoseseoseseesess 71 10 Useful Functions isiscisccccssseccstsveccececcccectosasoscsdsesessccosbssdescsecscsscoseevestaseseesessscasestdsesosesoeses 73 Database Functions nicer eter teet ada a ai 73 JavaScript Punctions ssssssssssssseseeee eene nene nennt tenente nennen 74 11T EocalisatiOnz anas iie reor recedere evo sioe eoo E eer vete ves cree enda soe e eerie eve ves Desa ved agen UT 75 Language Configuration Variables 75 Other Localisation Variables c cccccccccccssececssscesceccsssecesssscesseseess
51. any case it would not be meaningful Customising Filters Each time ERW has to display a list of entities relationships or files it can provide a filter to allow the user to restrict the available choices The default filter works on the content of the first attribute but it can be customised If several filters are specified they work in boolean conjunction Moreover multi value attribute specifier generate a filter that is satisfied if any of the values in the associated list satisfy the value in the filter To customise filtering you specify a list of attributes over which filtering must be performed Each attribute has a level that is a real number between 0 and 1 inclu sive with default 1 2 that expresses how significant that attribute is with respect to filtering Each list displayed by ERW has a default level too it is 0 for main lists 1 2 for selection lists and 1 elsewhere For each list ERW will display only those filter whose level is greater than or equal to the list level in definition order Thus by default main lists and selection lists get all filters whereas no filters are used elsewhere Note that relationship types without filters inherit the filters of their source target entity types The first array controlling filters is D type ilter More precisely for each attribute specifier the first key you can specify an ERW type second key type 33 Chapter 4 Customisation 34 an optional
52. ble id and produce the right data Chapter 4 Customisation The Button Inhibition Hook Sometimes you may want to keep the user from doing certain things such as cre ating new elements maybe providing your own buttons to do some custom pro cessing using the button hook ERW provides a button inhibition hook that allows you to select which of the standard buttons will be displayed The inhibition hook is activated by defining in the custom file of an entity an associative array named D type inhibit If there is an entry of D type inhibit whose first key is ok save clone or cancel the corresponding form button will not be displayed Moreover if there is an entry of D type inhibit whose first key defines the type of list as described in the Section called The Button Hook and whose second key is new modify delete select cancel add remove apply reset or chown then the corresponding button will not be displayed Inhibition can be set in the default customisation file The key chain is as above but you should use for the table name Thus for instance D inhibit clone eliminates the cloning button from all forms whereas D inhibit sel new eliminates the new element button from all selection lists Example 4 4 User front end Our librarian wants the users to be able to browse the database using ERW Of course users should be able to scan the available books and ma
53. ct from any other section titles You may add a section entitled Endorsements provided it contains nothing but en dorsements of your Modified Version by various parties for example statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front Cover Text and a passage of up to 25 words as a Back Cover Text to the end of the list of Cover Texts in the Modified Version Only one passage of Front Cover Text and one of Back Cover Text may be added by or through arrangements made by any one entity If the Docu ment already includes a cover text for the same cover previously added by you or by arrangement made by the same entity you are acting on behalf of you may not add another but you may replace the old one on explicit permission from the previous publisher that added the old one The author s and publisher s of the Document do not by this License give permis sion to use their names for publicity for or to assert or imply endorsement of any Modified Version Combining Documents You may combine the Document with other documents released under this License under the terms defined in section 4 above for modified versions provided that you include in the combination all of the Invariant Sections of all of the original docu ments unmodified and list them all as Invariant Sections of your combined work in its
54. cument free of added material which the general network using public has access to download anonymously at no charge using public standard network protocols If you use the latter option you must take reasonably prudent steps when you begin distribution of Opaque copies in quantity to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy directly or through your agents or retailers of that edition to the public Appendix A GNU Free Documentation License It is requested but not required that you contact the authors of the Document well before redistributing any large number of copies to give them a chance to provide you with an updated version of the Document Modifications You may copy and distribute a Modified Version of the Document under the condi tions of sections 2 and 3 above provided that you release the Modified Version under precisely this License with the Modified Version filling the rA le of the Document thus licensing distribution and modification of the Modified Version to whoever pos sesses a copy of it In addition you must do these things in the Modified Version Use in the Title Page and on the covers if any a title distinct from that of the Document and from those of previous versions which should if there were any be listed in the History section of the Document You may use the same title as a
55. custom form level but this is not necessary a custom form may decide for instance to modify just the order in which attribute are presented but not the specific interface that was chosen for each of them The advantage of a careful design based on specification percolation is that the ap plication is highly customisable but at the same time every change to one of the speci fications is immediately reflected in the user interface as it percolates freely through the following ones To clarify the usefulness of this approach we state a few examples In a complex database with a high degree of customisation and localisation the administrator has to add quickly a new entity type This is as simple as adding the new type to the ERL specification there is no immediate need to add all customi sation layers to the new type as it is guaranteed that the information contained in the ERL file will percolate down to the user interface producing a reasonable form in the default language Layers of customisation can be added later without disturbing the rest of the application e After defining a large number of custom forms we realise that a certain entity type will contain always a small number of entities Thus we wish that all many to one relations pointing at that entity type are displayed as sELECT elements i e a drop down list instead of using the standard display which is much larger In this case we just have to set up our ch
56. d Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format LaTeX input format SGML or XML using a publicly available DTD and standard conforming simple HTML designed for human mod ification Opaque formats include PostScript PDF proprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text Verbatim Copying You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and that you add no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute However you may accept compensation in exchange for cop
57. d SD loan filter startdate default 2001 01 01 D loan filter startdate operator gt would show at start loans that began in the current millennium Hooks allows you to customise part of ERW s user interface and database processing or even to insert your own code in the middle of ERW s They can be used to add your own custom buttons at the bottom of a list or to check that complex constraints on the content of the database fields are satisfied Hooks are set up by setting suitable variables in the customisation file Writing hooks require some understanding of ERW s internals you may also need to have a look at Chapter 10 A hook runs in a controlled environment with a separate variable namespace from the rest of ERW For your convenience all relevant global ERW configuration variables are accessible moreover for each variable a local copy without the _ERW_ prefix is defined Some hooks may pass you arguments they will be contained in the associative array Sarg the keys and the meaning of the values will vary from hook to hook 35 Chapter 4 Customisation 36 Caution The local copies are really copies if you modify them the correspond ing global ERW variable will not be modified In some cases this is not what you want Besides the global configuration variables the following ones are available _ERW_db A PEAR database connection You can use all PEAR s
58. d constraints is thus to write SOL views and constraints that incorporates your checks and call the functions from a post update or post delete hook 51 Chapter 6 Transaction Support 52 Chapter 7 Installation and Configuration Installing ERW is not a very complicated operation However there are several de tails that must be set up correctly in the environment for ERW to work The Run Time Environment The first step toward using ERW s powerful editing forms is installing all PHP scripts coming with the distribution the content of the php directory somewhere where they can be served by Apache These scripts contain the run time environment that produces the editing forms starting from the definition files produced by ERtool More precisely the file ERW php and the directory ERW can be installed in any place where PHP searches for source files i e usr share php whereas the remaining files must be placed in a directory served by Apache A reasonable option is to install all files in a generic place e g usr share ERW php and then create symbolic links but in this case you must be sure that the Apache FollowSymLinks option is on The second step is producing definition files with ERtool and making them accessi ble to the run time environment As a first try you should place the definition files in a directory named defs located in the same directory of the scripts it is the place where definition files
59. datory Key ti OE autienzations Pag Stat siartdate DATE x End enddate DATE rei date Book Type duration Ede typeis x Y 7 MECN aa Figure 8 1 An example of automatically laid out entity relationship diagram with hyperlinked documentation Chapter 8 ERtool The ERW Graphical Notation The diagrams created by ERtool use graphical hints to suggest cardinality constraints subtyping and identification functions The conventions used are unfortunately mostly idiosyncratic After a careful examination of the existing notations major theoretical or practical flaws where discovered In some cases the notation would have worked just for binary relationship types In other cases it was utterly counterintuitive Thus ERtool uses its own notation which is directly derived from Chen s but also borrows from the standard mathematical notation Object Role Modelling and a bit of fantasy Entity Types Entity types are represented by boxes containing the type label No attributes are shown as they are hyperlinked and can thus be easily accessed The border of ab stract types is dashed Figure 8 2 An entity type Figure 8 3 An abstract entity type Subtyping is represented by a dashed arrow from an entity type to its direct super type s Els Figure 8 4 An entity type with a subtype Weak entities are marked by a double frame as in standard entity relationship dia gram practise
60. dset gt lt p gt You can see loan details by clicking However you are lt em gt not lt em gt allowed to modify loan data lt p gt on them lt list ref person loan_book readonly true gt lt erf gt The resulting form would look as follows Notes Preface OK Apply Apply amp Clone Cancel First Name Ulrich Last Name Abel Address Whatever St 0 Wherever Card number 199247 Donation 601 000 00 You can see loan details by clicking However you are not allowed to modify loan data ith regular variation by Q Deng Short term 11 03 2002 14 03 2002 ith regular variation by Q Deng Long term 21 08 1950 Queueing systems with heavy tails by A P Zwart Long term 21 03 2002 21 04 2 Isls gt a 33734 Startdate f f End date f jJ sj ok Apply Apply amp Clone Cancel E Figure 7 A customised form with a read only relationship display Essentially we freely described a page where ERF input elements are replaced by ERW s input controls besides changing the look of the page using style sheet we can also set the size of the text inputs force elements to be read only and so on This example should have given a taste of ERW capabilities Browsing this manual you can also find how to generate documentation and graphical layouts To appreci ate the power of conceptual modelling you should think of schemata with hundreds of ent
61. e Each file stored in the fileset points to the entity it belongs to using the latter column Name isa A reference to a supertype Synopsis An entity type can inherit attributes and relationship types from any number of su pertypes The isa element specifies a supertype of an entity type Attributes entref The identifier of the entity this element points to Reification When you specify that A is a B ERW keeps in sync the tables reifying the two types i e for each entity in A there is a corresponding entity with the same id in B When ever you edit an entity of type 2 independently of whether you are editing it in the context of A or B ERW knows that it is of type A and acts accordingly Name ent An entity of an entity relationship schema Synopsis An entity type models a concept by means of attributes The ent element describes an entity type of an entity relationship schema It can contain text that describe infor mally its use or meaning and any number of isa and attr elements Attributes id A restricted identifier for this entity type 15 Chapter 2 ERL an Entity Relationship Language 16 label A label for this entity type The user will be always presented with this label when dealing with entities of this type abstract This field can be set to true or false the default In the first case the entity type is declared to be abstract see the Section called Subtyping in Chapter
62. e ERW adopts a restriction on the allowable assignments of sets to entity types it is required that every entity has a definite type For instance if A and B are both a c then it is not possible that an entity is in both a B and c unless it is also in a common subtype of A and B This avoids for instance that if man and woman are subtypes of person you can have an entity that is both a man and a woman but should you need that you just have to add a suitable subtype hermaphrodite of both man and woman Finally ERW lets you mark an entity type A as abstract In this case there can be no entity whose type is A but it is possible that there are entities whose type is a subtype of A Of course abstract types without subtypes are completely useless But should you need every person to be either a man or a woman or possibly a hermaphrodite you can declare person as abstract Mathematically the set of entities associated to an abstract entity type must coincide with the union of the sets associated to its proper subtypes Reification Now that we have a complete abstract account of the semantics of a entity relationship schema it is time to reify it this process maps our abstract multirelation theoretic semantics to actual tables of a relational database ERW handles the reification process for you in fact it has to handle it as the run time environment will have to query and update an actual database and there are several strateg
63. e the data you need the best thing to do is usually to open a new window and fill it with a suitable PHP script To this purpose the function openServiceWindow is available it opens a windows without navigation buttons and loads it with the URL given as first parameter the second parameter is a symbolic name for the window that is purely informative Example 4 3 Pretty printing a book data Our librarian now asks for the possibility of pretty printing the data of a book and of printing a report of all lends for a certain book It is easy to prepare a couple of PHP scripts doing that and outputting HTML By adding the following to the customisation file for the entity book these features will also be easily accessible from the main list SD book button list array array label gt Print data name gt data help gt Print all data related to the selected book events gt array onclick gt if i getSelectedId m book 0 alert No book selected else openServiceWindow data php id i data array label gt Print history name gt history help gt Print all loans related to the selected book events gt array onclick gt if i getSelectedId m book lt 0 alert No book selected else openServiceWindow history php id i history Of course the scripts data php and history php must have a look at the varia
64. ears in the form of a subscriber To do so you just need to put in the custom file for subscriber a suitable entry starting with SD person Caution Your custom files are executed as PHP scripts but they must emit no output In particular always check that there are no blank lines after the processing instruction delimiter gt The Type Array The definition file of an entity type relation type or fileset with attributes contains an associative array that specifies the type of each editable element whether it is an attribute or a relation A relationship type R from entity type A to entity type B is named z ain the definition file for a and r_a in the definition file for B The type array is named D type type all information from definition files is stored in a associative tree contained in the D variable By assigning a certain ERW type to a variable you can change the way it is edited For instance SD loan type duration r will tell ERW that in our library example the duration should be chosen via a check box rather than via a drop down list Note You can avoid quotes around r it is predefined as a constant by ERW so the lack of quotes will not generate any warning Customising Labels Each time ERW has to display an entity it uses a label for that entity The label auto matically set up is simply the content of the first attribute specified for the entity type but it can be cus
65. ed You can just browse this entry gt Of course the custom file for book will contain a line SD book postAuth bookPostAuth php Note that you can also access the usual variables available in a hook if the restriction does not apply to the users of group 1 then you can modify the hook as follows lt php if SuserGrp 1 amp amp ERW getOne year from book where id Sarg id Sarg auth update false gt The Selection load Hook The selection load hook allows to restrict the elements that will be displayed to the user in selection lists You can specify for each relation adjacent to the current entity a set of additional tables to insert into the from part of the SQL clause that will be used to fill the list and also a set of constraints that will be joined to the where part For instance S D person loadSel loan book from array loan SD person loadSel loan_book where array loan idl_book book id loan enddate is not null would restrict the books that can be borrowed to those that are not currently on loan Caution This hook is deprecated and may not be supported in future versions of ERW The Button Hook ERW provides editing for entities and relationships but there are other services that you might like to provide For instance a printed version of an invoice or a pretty printed version of the list of entities The butto
66. ema Synopsis The 1eg element describes one of the legs of a relationship type Description A leg is given by its codomain an entity type and information on the cardinality and editing constraints rel Chapter 2 ERL an Entity Relationship Language Attributes entref The identifier of the entity type this leg points to label A label for this leg The user will be always presented with this label when deal ing with the relationship type this leg appears in from the pointed entity type help A detailed help text for this leg for tooltips lower The lower bound for this leg It may be 0 the default or 1 upper The upper bound for this leg It may be 1 N or m the default key This field can be set to true or false the default In the first case the entity type referenced by this leg becomes weak and the entity type referenced by the other leg becomes one of its owners The cardinality constraint on this leg must be 1 1 and the one on the otherleg x N editable This field can be set to true the default or false In the first case the rela tionship type containing this leg will be editable from the entities of the pointed type Reification See rel Notes 1 Technically we defined legs on multirelations which are the semantics of rela tionship types but the reader will forgive us if we extend the term Name rel A relationship type in an entity relationship schema Synop
67. en a user holding insert privileges on a entity type creates a new entity the entity will have the user as owner and the user s primary group as group These two assignments determine the additional privileges Each type has separate user select group select user update group update user delete and group delete privileges The meaning is rather obvious for instance if user update is on then users have update privileges on the entities they own whereas if group delete is on then users belonging to the group of an entity or having has pri mary group the group of the entity have delete privileges on the entity Moreover each set of authorisations granted to a user or a group may add typewise or elemen twise additional privileges e g a user authorisation may grant to a certain user for a certain type just user select privileges In the end a user gets all authorisations granted typewise plus all elementwise authorisations granted to the user itselfs or to one of the groups the user belongs to To allow more flexibility even if user and group select privileges are granted you can tune in a finer way the entities shown to the user as explained in detail in the Section called The Selection Level Tuning Important Once you have update privileges on an entity you have the same privileges on all incident relationship that is you can insert delete or update any relationship involving the entity This is natural as relationships are
68. er respects regarding verbatim copying of that document Appendix A GNU Free Documentation License Aggregation With Independent Works A compilation of the Document or its derivatives with other separate and indepen dent documents or works in or on a volume of a storage or distribution medium does not as a whole count as a Modified Version of the Document provided no com pilation copyright is claimed for the compilation Such a compilation is called an aggregate and this License does not apply to the other self contained works thus compiled with the Document on account of their being thus compiled if they are not themselves derivative works of the Document If the Cover Text requirement of section 3 is applicable to these copies of the Docu ment then if the Document is less than one quarter of the entire aggregate the Docu ment s Cover Texts may be placed on covers that surround only the Document within the aggregate Otherwise they must appear on covers around the whole aggregate Translation Translation is considered a kind of modification so you may distribute translations of the Document under the terms of section 4 Replacing Invariant Sections with transla tions requires special permission from their copyright holders but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License provided that you also incl
69. fication functions to see an interesting example with subtypes see the Section called Customising Labels Suppose that every person is actually owned by a superhuman which is in turned owned by a god which in turn is a subtype of nonhuman Every nonhuman has a name If we want to know the name of the god indirectly owning a person referred in a certain loan we shall use person 0 ownedby superhuman refersto god nonhuman name where we assumed that the identification function from person to superhuman is named ownedby and that the identification function from superhuman to god is called refersto Following Arbitrary Relationship Types ERW does not pose any limitation on the kind of relationship type that you can in sert in an attribute specifier This means however that using non monodrome rela tionship types will lead to a situation where there are many values for the specified attribute and that it may happen that a pointer along the path is NULL in which case the resulting value will be the empty string For instance loan person lname specifies the last names of all people who borrowed a certain book Thus the associ ated value is a list of strings and not just a string The meaning associated to such a specifier depends on the context filtering labelling etc and will be fully explained later Custom Files 28 The first customisation layer is defined by means of customisation files By default they are cont
70. ges ERW locks all tables involved with the editing of an entity before starting the update Then it checks whether referential or logical integrity might be violated by the modifications submitted by the user then it checks that read only attribute values match the ones in the form then it perform custom checks using the pre update hook if any of the previous check fails the trans action is aborted Finally it applies the required modifications it performs custom updates using the post update hook and unlocks the tables Locking is important because it guarantees atomicity ERW does not assume fine grained locking in the underlying database rather it locks all tables that could be possibly involved with an entity update or deletion Unfortunately an unpleasant side effect is that in databases with a rich ownership subtyping structure updating an entity may require locking a large number of tables Note however that editing can be always carried out in parallel because of ERW s stateless editing design When changes are written to the database however the access will be suitably serialised Chapter 1 Overall System Design Notes In the future custom files will be replaced by another XML based language from which they will be generated Directed here means that arcs in the graph go from a node to another node that is they have a specified direction Usually entity relationship schemata defined without direction but this is
71. he execution of the post update hook the database is still locked This can be changed however if necessary The programmer must take into consideration that changing a lock implies that another transaction could sneak in maybe deleting the row just inserted If the lock is not modified the post update hook is executed atomically together with the pre update hook and ERW s update phase The Deletion Hooks Hooks exists also to track entity deletions They are activated similarly to the pre update hook and to the post update hook by assigning the variables D type preDelete and D type postDelete The behaviour is in all ways analogous to the update hooks except that the only information available is the global variable id containing the primary key of the entity that it is going to be deleted The Post Authorisation Hook The post authorisation hook is called just after the authorisations for the current element or type have been computed It is set by assigning to the variable SD type postAuth the name of a PHP file Note that the file is relative to the server directory where PHP scripts are installed When the hook is run the associative array arg will be loaded with three keys type providing the type for which the authorisation is being computed id provid ing the element of the given type for which the authorisation is being computed it will be 0 if the authorisation is not element specific and autn providing
72. he values of the two legs on the elements represented by a SQL row Note the index after id it is necessary as ERW support loops relationships from an entity to itself On the contrary a relationship R from entity A to entity B giving rise to a partial func tion is reified as an additional column named id amp 5 of SQL type int in A Injective relations whose transpose would be absorbable give rise to an error You just have to exchange the rA le of the two leg specifiers 1 Unfortunately the word attributes has different meanings in the XML and entity relationship world 2 Thisis actually an SOL 99 type but it is not supported by many DBMS 1 Technically we defined legs on multirelations which are the semantics of rela tionship types but the reader will forgive us if we extend the term Chapter 3 The User Interface This chapter describes the basic mechanisms and features of the web user interface generated by ERW It is not an end user manual As we mentioned before ERW lets you edit instances of an entity relationship schema That is it lets you create and delete entities and relationships and change their attributes Each entity has an associated form from which the user can modify its attributes and incident relationships To access the form the user must select the entity from the main list it is a list of all existing entities This list can be filtered in several ways and is generated by the script list ph
73. hen filesets and then relationships At tributes are listed in the same order as in the ERL file they are prefixed with their label and the label is embedded in a STRONG HTML element if the attribute is manda tory Of course this can be changed using custom forms If an attribute cannot be modified because it is read only it is displayed in a differ ent manner HTML input control get their READONLY attribute set whereas lists just display the available elements e g relationships on a grey background Warning Often browsers do not support the READONLY attribute on sophisticated controls such as drop down lists Of course ERW will just discard any changes but the user may not be aware of this fact Finally the user can select among four buttons any of which can be inhibited to finish editing OK as expected save changes and closes the form Save com mits changes but leaves the form open for further editing Save amp Clone commits changes and creates a clone of the current entity that can be further edited and saved this is most useful when doing repetitive data entry Finally Cancel will forget all changes You can tweak the default php script which generates the CSS style sheet to change some details In particular DIV elements of class 1istborder surround lists by choosing for instance the value scro11 instead of hidden for the overflow CSS attribute you can display lists with scroll bars
74. her elements so to maintain logical integrity Cascade deletions would break the local editing paradigm which is fundamental in ERW s design there is an exception to this rules for weak entities which are deleted together with any of their owners see the Section called Weak Entities in Chapter 1 Presently ERW handles binary relationships only If you really need relationships of greater arity you will have to simulate them using fake weak entities with mul tiple owners A Simple Example viii Maybe at this point you are curious about ERW but you still do not understand what it exactly does The easiest way to solve this problem is showing a simple example Suppose you have a library and you would like to keep track of which users have or had a certain book To this purpose you set up a simple entity relationship schema which has three entity types person subscriber and book Book are lent to persons but certain persons subscribed to the library and possibly donated some money The schema contains a relationship type 1oan going from person to book and this type has some attributes first of all the starting date startdate of the loan this attribute is clearly mandatory as there is no loan without a start then the ending date enddate of the loan this attribute is optional as the book could be currently out finally the attribute t ype that defines the type of the loan long or short term The informal description
75. ies If you distribute a large enough number of copies you must also follow the conditions in section 3 You may also lend copies under the same conditions stated above and you may publicly display copies Copying in Quantity 82 If you publish printed copies of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100 you must either include a machine readable Transparent copy along with each Opaque copy or state in or with each Opaque copy a publicly accessible computer network location containing a complete Transparent copy of the Do
76. ies to reify an entity relationship schema ERW follows a standard general purpose algorithm that should work reasonably in all circumstances Reification of entity types is fairly obvious each entity type is represented by an SOL table whose columns correspond to the attributes of the type there is some other work to do to support ERW extended types but we have not to concern ourselves with such details in this section and whose rows represent entities ERW adds an integer id primary key column to all tables so to mimic the set theoretic semantics we just discussed Additionally to support user group based authorisation two ad ditional columns id owner usrand id share grp might be added Even if the primary key is handled by ERW you still have the possibility of defining set of columns that should not be duplicated using the key attribute of the attr element of ERL The set of columns thus identified is declared UNIQUE If you do not declare keys you get a truly set theoretical semantics each entity is a distinguished object on its own even if it has exactly the same attribute values of another entity the same happens for relationships Reification of relationship types is more sophisticated the obvious way is using a support table whose rows represent relationships i e the elements of the multirela tion and the images of such elements under the two legs In our library example ERtool produces a table looking as follows
77. if any given in the Document for public access to a Transparent copy of the Document and likewise the network locations given in the Document for previous versions it was based on These may be placed in the History section You may omit a network location for a work that was published at least four years before the Document itself or if the original publisher of the version it refers to gives permission In any section entitled Acknowledgements or Dedications preserve the sec tion s title and preserve in the section all the substance and tone of each of the contributor acknowledgements and or dedications given therein Preserve all the Invariant Sections of the Document unaltered in their text and in their titles Section numbers or the equivalent are not considered part of the section titles Delete any section entitled Endorsements Such a section may not be included in the Modified Version 83 Appendix A GNU Free Documentation License Do not retitle any existing section as Endorsements or to conflict in title with any Invariant Section If the Modified Version includes new front matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document you may at your option designate some or all of these sections as invariant To do this add their titles to the list of Invariant Sections in the Modified Version s license notice These titles must be distin
78. iginal filenames fileSizeB fileSizeKB fileSizeMB fileSizeKiB fileSizeMiB Only for filesets contains the size of the file in the given unit note that K means 1000 Ki means 1024 and so on It is a float so you can format it using the stan dard printf conventions Displaying Owners and Groups ERW sets up two virtual relationship types owner_usr and share_grp that can be used as any other relationship type in an attribute specifier to display information related to an entity belonging to a type that has element based authorisation Displaying Relationships Display customisation allows you to specify a label using the attribute values of a relationship The resulting label will be juxtaposed on the right to the label of the related entity when displaying a relationship in an entity form For instance in Figure 2 loans are displayed showing the label of the borrowed book the related entity followed by a label derived from the relationship attribute values type of loan and dates Thus your labels for relationships must be written with this arrangement in mind for instance they would better start with a space However ERW allows you also to edit directly relationships In this case you may want to specify a more complex label possibly depending also on the attribute values of the entities related by the relationship 31 Chapter 4 Customisation 32 To this purpose ERW provides the D type fullDisplay custo
79. inally at the directory defined by the Java property it unimi dsi erw dtddir this property is automatically set by the ertool command using the content of the ERW DTD DIR environment variable Indeed setting this variable is the easiest way to guarantee that the ERL DTD will be available You can also set the variable manually using for instance java jar erw jar Dit unimi dsi erw dtddir amp directory filename Warning A common problem with running ERtoo1 is that it cannot find the ERL Document Type Definition DTD Often setting up an SGML XML sys tem is not so easy so the simplest thing to do is to put everything in usr share ERW dtd or to be sure that the current directory contains all DTD related files when running ERtoo1 you can copy them or create symbolic links or set up correctly ERW DTD DIR Options Without options ERtoo1 will simply read an ERL file from standard input and check it for syntactic and semantic errors However there are a number of options that will select a back end and produce useful output sql Activates the SOL back end The entity relationship schema is reified and com plete SOL code creating all necessary tables is printed to standard output This code can be saved or even directly piped into a database client defs Activates the definition back end A number of PHP files will be created in the current directory one for each entity type relationship type and for
80. ing a pop up JSCalendar will be added of course JSCalendar must be properly configured Note that if you choose jd and JSCalendar is not present the button will not ap pear but no errors or warnings will be generated The hour minutes type The user is presented with two text inputs for hour and minutes The fileset type The user with a set of input elements that allow one to upload files to the server possibly setting or editing their attributes r1 ris rit The type of an absorbed relationship type By default the user is presented with a set of input elements that allow one to select an entity to form a relationship The type rls instead simply creates a drop down list containing all entities among which to choose but clearly this is not a good idea if the entities are many The type of the transpose of an absorbed relationship type By default the user is presented with a set of input elements that allow one to select an entity to form one or more relationships Chapter 4 Customisation rlwrle The type of the transpose of identification functions The types rlw and rle are thought for weak entities and they lets you create new entities that will be auto matically owned by the current entity There is however an important difference for the rle type the editing is embed ded the attributes of the other entity are embedded into the form of the main entity and the user can modify and edit them much in the same way a
81. ionship type whereas the list showing relationships is named r relationship type e lists that lets the user edit a fileset are named entity type attribute name Said that you can use the following functions to discover which element of a list has been selected by the user int getSelectedId elemId Given the identifier of a list this function returns the SOL identifier i e the value of the id column of the selected element int getSelectedItem elemId Given the identifier of a list this function returns the 0 based index of the se lected row void openServiceWindow url name This function opens a new window without toolbar menus etc and loads it with the given URL The given name will be juxtaposed to the current number of milliseconds to generate a name for the window so that two activations of the same button actually open two different windows You should look at the example given in the Section called The Button Hook in Chapter 4 Chapter 11 Localisation All ERW strings can be easily localised using the GNU gettext package It is a fairly standard way of giving translations of literal strings in various languages and you can find documentation about it at the GNU site Moreover there is limited support for some locale dependent quirks such as the decimal point There is also support for UTF 8 using the PHP mbstring extension Language Configuration Variables Locales country specific language
82. ionship type is said to be many to many Chapter 1 Overall System Design However relations satisfying the restrictions above have standard mathematical names which we will use in what follows More precisely we shall use the obvious extensions of these names to multirelations A multirelation R from X to Y is said to be total if for each element x in X there is at least one r in R such that R r x monodrome or a partial function if for each element x in X there is at most one r in R such that R r x surjective if for each element y of Y there is at least one element r of R such that R r y injective if for each element y of Y there is at most one element r of R such that R r y a relation if there are no distinct elements r and s of R such that R r R s and R r R s Intuitively a multirelation is total when every element of its source is related to some thing itis monodrome if every element of its source is related once with at most one element of its target it is injective if every element of its target is related once to at most one element of its source it is surjective if every element of its target is related to something and it is a relation if elements are never related twice These properties are strictly related a multirelation is total if and only if its transpose is surjective and it is monodrome if and only if its transpose is injective finally it is a relation if and only if its tran
83. is type can assume a finite and fixed number of values and the set element can be used to create fileset types fileset attributes associate to an entity a set of files with attributes Inside an ent element there are attr elements describing attributes and isa ele ments describing supertypes The attr element has some XML attributes that let you specify the type of the attribute and whether it is mandatory that is whether the user must provide some input for that attribute Inside a rel element you can find again attr elements but you will certainly find two 1eg elements which specify the first and second leg of a multirelation including the source entity the target entity and cardinality constraints All elements let you insert optional text inside them it will be added to the docu mentation Types and Identifiers Almost all elements in an ERL document have a mandatory identifier For the er1 ent rel and attr elements moreover the identifier is bound to be restricted it must start with an alphabetical character and must be entirely formed by alphanumerical characters Case sensitivity cannot be guaranteed as it depends on the underlying database but ERW is case sensitive so be careful Note that the identifiers id file owner share and belongs are reserved Warning You can use identifiers of any length but they will be combined dur ing the reification process to get the actual name of database columns
84. it as of either of the two types Fixing a choice i e the most specific type doesn t help much as you would have redundant and possibly nonvalid information in A The solution chosen in the design of ERW is based on two principles 1 If an entity type has element based authorisation all its subtype have it too 2 Only root types may have element based authorisation A root type is an entity type that is maximal i e it has no proper supertype and such that all its subtypes have exactly one maximal supertype In other words a root type is the maximum type of the type hierarchy it belongs to For instance if A is a B and also a c then B and c are maximal but they are not root types So no type in this hierarchy may have element based authorisation If however we have an additional type D such that both B and c are p then p is a root type and by requiring element based authorisation for D we will get it for all subtypes of D In practise if you do not have type hierarchies you can use element based authorisa tion at will If you have type hierarchies you can use it only on hierarchies having a maximum type If you really need several maximal types you can always add a fake 49 Chapter 5 Authentication and Authorisation root type without attributes having all maximal types as direct subtypes and maybe make it abstract Notes 1 Of course nothing prevents you from using the post update hook to set up spe ci
85. it generates a graphical representation of the schema and documentation about the reification process this documentation allows you to understand exactly how the process was carried out And last but not least it generates a set of configuration files written in PHP These files when fed into the provided run time PHP environment generate a set of forms that allows easy editing of the database A flexible customisation process allows you to tune the forms to your needs Where is the difference with other web based database administration tools The point is that ERW knows the abstract structure of the database and thus can offer a much more sophisticated interface to the user In particular the user never sees an SQL table rather it is presented with relation based operations such as associate this element to this element The run time environment using the configuration files produced starting from the ERL file will modify the database tables correspondingly Just to make a comparison a tool like PHPmyAdmin is to ERW as a disassembler is to a compiler run time environment You can of course use PHPmyAdmin to do raw ad ministration of the database tables generated by ERW but the knowledge that ERW has of the abstract structure of the entity relationship schema gives it the possibil ity of interpreting the same tables in a deeper way Of course ERW can only edit databases reified by ERt ool so it is less general These are
86. ities complex type hierarchies and ownerships which ERW will handle with the same ease 1 http www gnu org copyleft gpl html 2 http pear php net xiii Preface xiv Chapter 1 Overall System Design ERW is a complex system with many interrelated components so before starting to describe in detail each part it is a good idea to review a bit more technically the procedure to generate and manage a database using it T The first and most important step is the creation of an ERL file ERL is a simple XML based language that describes entity relationship schemata decorated with additional information pertaining the actual database structure such as the SOL types of the attributes and some editing information such as which relationships can be edited in an entity form ERL has also support for simulated SOL types that is additional types that you can use as if they where actual SOL types They include for instance boolean and enum Then you have to create your database This is accomplished using ERtoo1 a tool written in Java that reads ERL files and produces a number of outputs The first usage of ERtool is to generate SOL code creating the actual database Note that in this phase ERtoo1 has to reify the entity relationship schema that is to decide how to implement in the relational model the entity relationship schema given in the ERL file ERtool can also generate documentation on the reification process so
87. ity constraints restrain the possible multirelation that an instance can assign to the relationship type For each of the two entity types you can specify a pair of indices between parentheses and separated by colon as in 1 N The left character may be 0 or 1 while the right character may be 1 N or M The specifiers assigned to a relationship provides restrictions on the cardinality i e the number of elements of certain relationships in an instance of the schema More precisely if the first character is 0 it imposes no bound e if the first character is 1 it forces each entity to be in relation with at least another entity e if the second character is m it imposes no bound if the second character is N then a multirelation instantiating the relationship type must be a relation that is it cannot happen that entities are related twice e if the second character is 1 it forces each entity of to be in relation with at most another entity and it must be related once In other words the first index is a lower bound on the cardinality of relationships involving an entity while the second index is a sort of upper bound There are some standard names if the two pairs of indices are of the form x 1 then the relationship type is said to be one to one if one is of the form x 1 and the other of the form x N then the relationship type is said to be one to many finally if the two pairs are of the form x N then the relat
88. ivated web pages are output in UTF 8 input from the browser is read in UTF 8 and data exchange with the database if performed using UTF 8 strings This influences a number of settings going from the DBMS internal encoding to the terminal encoding that must be set up correctly Note that usually an 8 bit clean database with work flawlessly with UTF 8 support as UTF 8 has several good properties e g lexicographical byte by byte ordering co incide with lexicographical character by character ordering Warning By default ERtoo1 will generated definition files using ISO 8859 1 As long as none of your labels enumerative types etc is not US ASCII this is not a problem If however you plan to use arbitrary UTF 8 char acters in your labels you should use the UTF 8 backend when produc ing definition files with ERtool l http www gnu org 2 mailto vigna acm org Chapter 12 Script Reference This chapter gives an overview of the purpose of some scripts coming with ERW Its main purpose is to make you able to create a custom portal for access to the ERW editing and customisation pages ERW checkERW php This script is never called during editing It checks the structure of definition files and custom files looking for mistakes in array keys parameter types and so on It is a fundamental tool as it is easy to make a typo For a correct setup it should give no message There are two ways to run this script either
89. l del s lt gt gt gt 2L f 1 5 7 5483 Add New Person 7 Modify Last Name First Name Enable filter Clear filter OK Apply Apply amp Clone Cancel Figure 2 An ERW form for a book The first input elements allow you to edit the attributes of a book note that you can upload a description text file However the rest of the form is concerned with editing a relation there is a list of entities persons that borrowed the book in this case and you can create and delete relationships or change their attributes Analogous forms exists for persons but here we have an interesting feature Preface v Person Mozilla NN Person Walter G Aiello John Walter Baker Walter Benz Walter Bergweiler Walter A Burkhard Waters Wassiljewiesch Gorlow ND Walter Kurt Hayman Walter Jacobs Kenneth Walter Johnson Wallace Kantor Walter Kern Walter Ledermann John Walter Lee Walter M Lioen Walter Maxones Us _s lt lt l gt gt gt fs 7 2a New Person Modify Delete Last Name First Name Wal Subscriber Clear filter EL Figure 3 An ERW list where you can choose persons Note that you have the choice when creating a new person to make a subscriber or not In general you can select any of the subtypes of the current entity type In any case if you edit a person you will get the right f
90. lAreaConfig function var config new HTMLArea Config config pageStyle body background color white config erwPlugins erwPlugins return config Caution HTMLArea is fantastic in theory but it is a very fragile piece of software For instance if any of the plugins you are using has no translation for the current language HTMLArea will not start without giving any message Always check that you have translations for all plugins you use in all languages specified in _ERW_supportedLocales configuration variable we use the first two letters of the locale to select HTMLArea s language A reasonable trick is to add all missing languages as soft links to the English version and be sure that your server follows soft links Another relevant problem is that as of this writing HTMLArea ruth lessly overwrites the unload event handler As a result users closing a window after having made some changes will not be warned that their changes have been lost The only solution is removing manually from HTMLArea s code the guiltly lines search for unload in htmlarea js Moreover HTMLArea does not call the change event handler when the text changes As a result changes performed in an HTMLArea text edi tor will not cause warning messages about changes being cancelled or lost Configuring FCKeditor FCKeditor is a more supported alternative to HTMLArea Also FCKeditor works only on Gecko based browsers a
91. label second key label if the label is omitted the label of the attribute will be used instead and an optional filter level second key level default 1 2 Presently the ERW type must be the default ERW type associated to the ERL type of the attribute except for the ERL type a for which the type t must be used Since there is a default filter and many levels of keys it is usually a good idea to first reset the array and then fill one by one the desired entries As an example SD book filter array SD book filter author type t SD book filter author label Author s SD book filter title type t SD book filter isbn type t SD book filter isbn level 0 1 will allow to select a book by author title and ISBN code in the main list but just by author and title elsewhere Moreover the author filter will be labelled Author s You have the full power of attribute specifiers at your disposal For instance you can filter subscribers on their first and last name SD subscriber filter array SD subscriber filter person fname type t SD subscriber filter person lname type t Multi value attributes may be very useful too assuming you want filter out books that have been lent to someone in particular SD book filter array SD book filter loan person lname type t
92. license notice The combined work need only contain one copy of this License and multiple identi cal Invariant Sections may be replaced with a single copy If there are multiple Invari ant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in parentheses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections entitled History in the various original documents forming one section entitled History likewise combine any sections entitled Acknowledgements and any sections entitled Dedications You must delete all sections entitled Endorsements Collections of Documents 84 You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single copy that is included in the collection provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects You may extract a single document from such a collection and distribute it individu ally under this License provided you insert a copy of this License into the extracted document and follow this License in all oth
93. luded and its return value that you can set using the return instruction is checked If it is the empty string or nu11 the check is considered successful Otherwise the returned string is considered to be an error message the changes will not be applied the string will be displayed and the user will be presented again with the form he or she was trying to submit Note that in the case there are supertypes pre updates hooks are called starting from the max imal supertypes i e supertypes that have no proper supertype and going down to the actual type Pre update hooks for embedded entity relationship and fileset types are executed afterwards To help in writing parametric scripts the run time envinronment sets up four global variables Chapter 4 Customisation SmainType The entity or relationship type of the element modified or created by the form currently processed mainId The numerical identifier primary key of the element that caused the current hook invocation or 0 in case the element is new Stype The entity relationship or fileset type of the element modified or created by the hook currently processed This might differ from mainType because of embed ded editing of relationships weak entities or filesets Sid The numerical identifier primary key of the element that caused the current hook invocation During the execution of the pre update hook you can access a read only global vari able q
94. means that derivative works of the doc ument must themselves be free in the same sense It complements the GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this License is not limited to software manuals it can be used for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference Applicability and Definitions This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language A Secondary Section is a named appendix or a front matter section of the Doc ument that deals exclusively with the relationship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that
95. mewhere in you PHP configuration file Include paths PHP must be able to retrieve both PEAR scripts and ERW run time scripts A rea sonable setting which however may very depending on your operating system and distribution is include_path usr share pear usr share php if you installed the scripts as suggested in the README Logging ERW is a complex system and heavy logging can be really useful when you do not know what s happening You should activate all warnings and log them to a suitable file ERW tries to never use a variable that it is unset so that you can easily track typos in variable names It is not a good idea to output errors on the page being generated as they will disturb the output more than necessary A suitable setup for instance is error_reporting E_ALL display_errors Off display_startup_errors Off log_errors On error_log var log httpd php_log Note that the log file must be writable by the user running Apache Large uploads If you plan to use filesets and foresee uploads of large documents you should probably set the suitable PHP variables to suit your needs for example memory_limit 20M post_max_size 20M upload_max_filesize 20M If you plain playing with filesets it is probably also a good idea to override the default upload_tmp_dir Configuring HTMLArea HTMLArea support is a bit experimental but it works Essentially you can use an ERW type ha
96. misation vari able A good example for loan is the following one which would give the output shown in Figure 6 SD loan fullDisplay fmtString 10 10s 10 10s 36 36s 10 10s 10 10s SD loan fullDisplay head First name Last name Book title Start date SD loan fullDisplay field array person O0 fname person_O lname book l title startdate enddate Accessing subtypes The qualifier part of an attribute specifier may be also used to access attributes of a subtype Of course the attribute could not exist at all because the entity specified is not of that type in this case the value will be NULL Interestingly we can use this fact to build labels that are conditional on the type of an entity For instance if we have an entity document with attribute t it1e and subtypes publication with mandatory attribute journal and techrep with mandatory at tribute number we can specify a label like SD document display fmtString s s s s s d s SD document display field array title publication journal techrep number As a result each document has an optional item between parentheses if it is a publi cation or a technical report the journal or the number respectively We can push further this technique exploiting the ubiquitous id attribute Since sub typing is realised by set inclusion an entity with a certain id is
97. n hook allows you to add buttons at the bottom of lists that invoke JavaScript actions which could in turn open new windows that would be filled by PHP code The button hook is activated by defining in the custom file of an entity or of a fileset an associative array named D type button The first index is the kind of list you want to attach the button to Possible value are main meaning that you will add 39 lt 1950 Chapter 4 Customisation 40 buttons to the main list sel meaning that you will add buttons in all lists used to select entities to relate to the current entity re1 denoting a list of relationships and fset denoting the list of files in a fileset The value of the array for each index must be again an array where each element describes a button Each element is in turn an associative array with keys label name help and events The values of label and name will be the name and the label of the button whereas the value associated to the events key is an associative array having as keys event attributes onclick onmousedown etc and as values fragments of JavaScript code to be executed The value of the help element will be displayed as a tooltip when the mouse passes over the button Each relevant HTML element in a page generated by ERW has a well defined identi fier The main list for the entity Ais named m a There are a number of useful functions that let you access the JavaScript state Once you hav
98. n time environment so that you can for instance do some post processing after every database modification If you need more flexibility in the user interface custom forms can be used to pro vide a highly customised appearance Custom forms are written in an XHTML like language so you can use style sheets etc Finally you may want to change the structure of your database From the user interface viewpoint this can be done in a breeze as it is just a matter of modify ing the ERL file and regenerate the definition files However the changes to the database structure must be handled manually Usually it is a good idea to keep a copy of the previously generated SQL statements and see the differences In any case simple changes such as adding or removing attributes entities and relation are almost effortless and the checkdb php script can help you by pointing out discrepancies between definition files and SOL tables Chapter 1 Overall System Design Entity Relationship Schemata To understand each other throughout the rest of this manual we have to set up a minimal common language Unfortunately many terms in the database world are not completely standard and can vary depending on the textbook you have A rad ical choice made in this manual is to replace whenever possible database related names for sets and functions with the more standard and more stable terms used by mathematicians If you never heard of entity relationshi
99. nd Explorer First of all you must download and install FCKeditor 2 or higher and set a suitable configuration variable Then FCKeditor can be easily configured using XML and some JavaScript files Caution The warnings given for HTMLArea are valid also here In particular at the time of this writing FCKeditor has no officially supported way to set its content after it has been created so ERW must dig into its internals Configuring JSCalendar JSCalendar can be used to add to date input fields a button that let that user choose a date using a pop up calendar For the time being configurability is limited Essen tially you can use an ERW type jd to specify that a JSCalendar button should be added to a date attribute if JSCalendar is not configured you will not get the but ton JSCalendar should work on all browsers supported by ERW First of all you must download and install JSCalendar or higher and set a suitable configuration variable Then there are several ways to customise JSCalendar For the time being you can only configure the look of the calendar by setting a suitable style sheet to be loaded The default ERW style sheet shows how to load a style sheet 58 Chapter 7 Installation and Configuration Caution The warnings given for HTMLArea are valid also here Be very careful in particular with translations which are selected automatically Notes 1 http www htmlarea com 2 ht
100. nd describes a list of value label pairs Any attribute of type enum pointing by means of the enumref attribute to a certain enum element will have the SOL type of that element moreover the content of the attribute is restricted to the values described in the enum element and for each value the user will always be presented with the corresponding label In such a case we say that we defined a static enumerative attribute If on the other hand there is no enumref in an attribute with type enum then a special table is created that holds the value label pairs The value label pairs can be edited by authorised users and so we speak of a dynamic enumerative attribute Clearly this kind of enumerative attribute is more flexible but also less efficient The fset type Filesets are a rather sophisticated object in fact a weak entity type camouflaged as an attribute An attribute of type fset does not generate an SOL column instead it generates another table that holds information about files associated to entities When editing an entity the user will be able to upload and download files associating them to the entity much like a weak entity As an additional facility files in a fileset may have attributes for instance language or a title To obtain this result a fileset type defined using the set element must be referred using the fset ref attribute Of course you cannot use the fset type when defining the attributes of a file set
101. not however the only advantages of using ERW We list some of them ERW has support for a wide range of features of the extended entity relationship model including multiple inheritance and multiple owners ERW is entirely based on international standards and open source tools Since ev ery part of the system is known and documented you are never left with an un usable bunch of data or outdated form generating scripts that no one remembers how to modify The system moreover is largely architecture independent ERW is free software distributed under the GNU General Public License How ever applications built using ERW may be distributed under the license of your choice similarly to what happens to programs compiled with a free compiler ERW maintains referential and logical integrity of your database That is to say not only editing cannot create dangling references but also the cardinality constraints you have imposed will be automatically enforced for instance if every document must have an author then it will be impossible to insert a new document without associating it with an author e ERW allows any number of users to access the database concurrently ERW uses the W3C DOM to offer a rich and intuitive graphical interface This interface comes at no cost once you have defined your entity relationship schema in ERL ERW supports gettext and UTF 8 everywhere you can create forms and handle content in any lang
102. nstallation and Configuration 54 _ERW_dbUser The user name with which to access the database _ERW_dbPassword The password to access the database as the user _ERW_dbUser _ERW_defsPath A relative or absolute path specifying the directory where the ERt oo1 generated configuration files are stored ERW customPath A relative or absolute path specifying the directory where the custom configura tion files are stored ERW formsPath A relative or absolute path specifying the directory where the custom forms are stored ERW utf8 If set to true this variable enables UTF 8 support _ERW_htmlArea If set to a string this variable enables HTMLArea support The string must be a path which can be relative to the document root leading to the HTMLArea installation usually installing HTMLArea in the document root in a directory named htmlarea and setting this variable to htmlarea is a good choice _ERW_fckEditor If set to a string this variable enables FCKeditor support The string must be a path which can be relative to the document root leading to the FCKeditor installation usually installing FCKeditor in the document root in a directory named fckeditor and setting this variable to fckeditor is a good choice ERW jsCalendar If set to a string this variable enables JSCalendar support The string must be a path which can be relative to the document root leading to the JS
103. o disable all custom hooks and scripts If everything seems to be fine from the PHP side check with Mozilla and its JavaScript console that no JavaScript errors are generated Please try with the last Mozilla version before doing any bug reporting Reporting Bugs 80 If you really think you hit a bug please report it It is important that you provide the ERL file that generates your database any custom file that are necessary to replicate the bug but check carefully that the problem does not lie in the custom files PHP HTIP server and JavaScript logging Without these items it is virtually impossible to diagnose a problem Appendix A GNU Free Documentation License Version 1 1 March 2000 Copyright 2000 Free Software Foundation Inc 59 Temple Place Suite 330 Boston MA 02111 1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document but changing it is not allowed Preamble The purpose of this License is to make a manual textbook or other written docu ment free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either commercially or noncommer cially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which
104. oad a file into the text area If you choose the ha type then on browsers supporting HTMLArea you will get a 25 Chapter 4 Customisation 26 ip nns d jd WYSYWYG HTML editor of course HTMLArea must be properly configured Analogously for fa and FCKeditor The second most common type an integer There is no check on the actual di mension of the number inserted by the user as it could depend on the DBMS The type p forces its content to be strictly positive The exact numeric types These types require a size and a scale in their decla ration so ERW can check that the user is not inserting more digits than allows The type ns presents the same data in separated and localised form that is the user can use a localised comma and a localised point and moreover the num bers inserted will be automatically thousand separated if they are not already as the user leaves the input field A dynamic enumerative type The user is presented with a drop down list A static enumerative type The user is presented with a drop down list with type s and with a radio button set with type r Note that it is not a good idea to set type r for a non mandatory attribute as the user has usually no way to deselect all buttons The boolean type The user is presented with a checkbox The date type The user is presented with three text inputs for day month and year If you choose the jd type then an additional button open
105. oc of ER 2002 Lecture Notes in Computer Science Springer Verlag 2002 This semantics is much more precise and natural than the tuple semantics of relational databases and in fact it is a good idea to think of relational databases in set theoretic terms whenever you can Cardinality Constraints An important feature of entity relationship schemata is the possibility of specifying cardinality constraints These are instructions of the form every person has exactly one mother or every document must have at least an author but possibly many There constraints are useful because they allow to maintain the logical integrity of the database in a logically integral database you can always trust a document to have an author and you can avoid to check if it is missing ERW maintains automatically the logical integrity of your database An important point often missed about logical integrity is that it is a feature of the semantics of the entity relationship schema not of the underlying relational database It must be expressed abstractly in term of properties of multirelations and not in term of the particular relational implementation of the entity relationship schema ERW uses a slight extension of the standard way of giving cardinality constraints on relations as it has to handle multirelations Recall that each relationship type is an arc going from an entity type the source to another entity type the target Cardinal
106. of an entity or to edit weak entities directly into the form of the owner The main difference is that non absorbed relationship types and filesets cannot be part of an embedded form A Quick Tour Before giving the reference to ERF elements it is useful to have an informal discus sion of what you can describe in ERF ERF documents looks really like XHTML documents Indeed ERF contains a selec tion of XHTML elements e g div style ecc and a custom form looks like a sim plified XHTML page The interesting point however is that placing suitably input and list elements you can place freely ERW input controls and lists along the page If you want to have a look at sample ERF custom forms ERtoo1 can produce for each type a form giving the standard look For instance the form produced for a person looks as follows lt xml version 1 0 gt lt DOCTYPE erf PUBLIC DSI DTD ERF V1 0 EN file erf dtd gt erf ref person gt input ref fname gt input ref lname list ref loan book erf A corrsponding customised form has been shown in the Section called A Simple Example in Preface more precisely in Figure 7 Chapter 4 Customisation Elements In this section we list all ERF elements giving in detail their usage and meaning First of all there are XHTML like elements n1 h2 h3 h4 h5 h6 div fieldset p span em strong i b sup sub samp code var legend and img which
107. of the attribute See attr scale For numeric types the scale that is the number of fractional digits See attr Name fset A declaration of a fileset type Synopsis A fileset type specifies which attributes each file of the fileset will have The fset element contains a list of attr elements to this purpose Attributes id An XML identifier for this type label A label for this type mainly for documentation purposes Reification A fileset type declaration does not per se generate any SQL code However it defines the content of the support tables for all attributes of type fset that refer to the type as all attributes listed inside the element are reified and added to the table Name attr An attribute of an entity or relationship type Chapter 2 ERL an Entity Relationship Language Synopsis The attr element describes an attribute of an entity or relationship type Attributes id A restricted identifier for this attribute Note that the identifier is not an XML identifier so you can use the same attribute identifier for attributes of different types label A label for this attribute The user will be always presented with this label when dealing with the attribute help A detailed help text for this attribute for tooltips type An ERL type for this attribute If not specified it is assumed to be VARCHAR enumref If the type attribute is set to enum and you want to specify a static enumerative
108. of the entity relationship schema that we have just given is formalised by the following ERL document lt xml version 1 0 gt lt DOCTYPE erl PUBLIC DSI DTD ERL V1 2 EN file erl dtd gt erl id library title A Library gt amp ERWauth enum id termlen type char size 1 gt enumval value L label Long term enumval value S label Short term gt Preface lt enum gt lt ent id person label Person gt lt attr id fname label First Name size 30 mand true gt attr id lname label Last Name size 30 mand true gt ent ent id subscriber label Subscriber gt lt isa entref person gt lt attr id card label Card number type int mand true gt lt attr id address label Address mand true gt attr id donation label Donation type numeric size 11 scale 2 gt lt ent gt lt ent id book label Book gt lt attr id title label Title mand true gt lt attr id author label Author size 40 mand true gt lt attr id publisher label Publisher mand true gt lt attr id isbn label ISBN Code gt lt attr id year label Year type integer gt attr id description label Description type text lt ent gt lt rel id loan label Loan gt lt attr id startdate label Start date type date mand true default 2001 01 01 attr id enddate label End date
109. of these frames ERW will do it but in case something goes wrong the starting height can be tuned by the administra tor or even by the user ERW useFieldsets ERW uses the FIELDSET element to group items In some very old browsers such elements may cause layout problems In this case you can set this variable to false ERW useOriginal Since 1 0 10 ERW keeps track of the original filename of each file in a fileset This feature however is disabled if not enabled explicitly by setting this variable to true as it is not compatible with previous versions The default configuration file sets this variable to true so that original filenames are enabled by default in new installations Configuring PHP 56 There are also a few option that must be set up in PHP for ERW to work No magic quotes All magic quote options must be turned off More explicitly magic_quotes_gpc Off magic_quotes_runtime Off magic_quotes_sybase Off To be true only the first line is strictly necessary ERW can turn off the other settings internally The separator ERW uses the W3C endorsed separator for separating the query part of a URL The original symbol the ampersand was not well thought as it should be really written amp amp You should add the line arg separator amp or arg separator input amp Chapter 7 Installation and Configuration depending on your PHP version so
110. oice during the customisation phase so that it will percolate correctly to the forms even if they are customised We decide that we need an additional attribute in an existing entity type Of course the new attribute will immediately show up in the default form However if there are custom forms for that entity type they are likely not to contain the new at tribute ERW detects this situation and adds automatically the attribute as hid den it will be silently preserved when editing the database and filled with its default value The administrator will be warned that it is the case to modify the custom forms accordingly but again consistency will be maintained User Interface Customisation 24 The user interface provided by ERW can be customised in several ways but the most important point is that the same data can be presented in different ways By default ERtool will use an interface that will work in every case however it could not be the best interface for a particular case For instance if a relationship is absorbed ERW present it as a complex set of user inputs where the user can filter and choose which element to associate to the current one However if the choice is among a very small number of elements a drop down list could be a better choice Chapter 4 Customisation In this section we will first review some general idea about customisation then we will see how to write custom files and finally cu
111. ol checks that there is no cycle formed by total relationship types To insert an entity in a type belonging to the cycle you need to relate it with some other entity and this initially impossible However if you manually insert some data in the entities the problem is solved so ERtoo1 will just warn you Finally it is necessary to make sure that it is impossible that an instance of the schema contains two distinct ownership paths between two entities in particular it must not be possible that an entity owns itself to this purpose ERW uses a novel algorithm that is able to discover statically if such paths can exist looking at the type structure of the schema Error Messages Most error message of ERtoo1 are self explanatory We gather here the most obscure ones A relationship type must be multi in both legs or none As explained in the Section called Entity Relationship Schemata in Chapter 1 car dinality constraints have some restrictions if you ask for a multirelation on one leg you must do the same on the other You cannot declare bijections if both legs have upper 1 one leg must have lower 0 Bijections are of no use in ERW because they make entities impossible to create or delete as the entity sets adjacent to bijections must always have the same number of elements You cannot declare injective relations that are not partial functions they must be transposed An injective relation is the transpose of a parti
112. one and the following one are marked as dead and will not be actually printed note that an optional directive cannot be marked as dead This allows you to build complex specifications that add markup such as brackets hyphens and so on depending on the presence of a certain parameter As an example SD book display fmtString s s s s s SD book display field array title author isbn would display a book by showing the author followed by a colon the title and then the ISBN code between parentheses but only if the code has been specified Warning There are situation such as editing weak entities with ERW type rie in which ERW has no way to know the attributes of other entities In this case they are all set to NuLL Your format strings must always be written so that they handles these cases gracefully The other useful extension allows to format lists of formatted values using a given separator and additional formatting More precisely ERW accepts directives of this form S alignment width precision length separator standard format specifier When printing a directive of this form ERW expects as corresponding field a multiple value attribute Each element of the list of values will be formatted using the standard format specifier Then the resulting strings will be concatenated using the given separator which can also be delimited by or and finally the
113. orm a subscriber for instance will get something like this 9 Subscriber Ulrich Abel Mozilla OK Apply Apply amp Clone Cancel First Name Ulrich Last Name Abel Card number 199247 Address Whatever St 0 Wherever Donation 601 000 00 r Borrowed Queues with regular variation by Q Deng Long term 1 Queueing systems with heavy tails by A P Zwart Long term 21 03 2002 21 04 2 de 991 5 gt gt gt Eim Remove Start datef fe 960 Enddae Typeloratem Reset Assi Algebraische Grundlagen der Informatik by K U Witt Fractional evolution equations in Banach spaces by E G Bajlekova Queueing systems with heavy tails by A P Zwart Scattered spaces with respect to spreads and eggs in finite projective spaces b is _ss lt gt gt gt gt 1 5 19 Add Newitem Modify Author Title Enable filter Clear filter OK Apply Appy amp Clne Cancel Figure 4 An ERW form for a subscriber You can also have a list of subscribers only in this case you can choose to have also cynical filters such as the amount of donation v Subscriber Mozilla Peter Arthur Barry Pleasants Yuval Rabani Reza Rashidi Stephen M Robinson Shmuel Safra Prashant Saxena Jack Snoeyink Lawrence Snyder Bo Aagaard Sorensen Jorge Soto Andrade lt lt lt gt l gt
114. p Once the user selects an entity for editing a new window is opened that contains HTML input controls for attributes text inputs text areas radio buttons etc and a number of complex structures for editing relationships The content of the window is generated by the script form php The rationale behind the editing of relationships is that you have a white background list containing the current relationships and immediately below a grey background list of entities that could be used to create new ones Suitable buttons allow the user to perform relationship editing For convenience buttons that allow to create new entities or modifying existing ones are also allowed but they can be inhibited Editing relationship attributes is also fairly easy there is a set of input controls un der the list of relationships All new relationships get the attributes currently dis played Moreover whenever the user clicks on an existing relationship its attributes are loaded into the controls in this way it is easy to copy the attributes of an existing relationship If the user wants to modify the attributes of an existing relationship he or she has just to click on the relationship modify the controls and click on the Apply button which will apply the current values You can help the user to understand what s going on my making good use of the help attribute for attr and leg elements By default ERW displays first all attributes t
115. p schemata or of their graphical counterpart entity relationship diagrams however we suggest you to have first a look at a good textbook on the subject Entities model things of the real world In our library example a specific person and a specific book are both entities because these are the things we want to model we could call entities things but this would not sound very scholarly Each entity has a type Entity types model concepts in our example entity types will be person subscriber and book To an entity type we associate usually a set of attributes that is pieces of information the book title the person name the subscriber donation and so on Each entity defines a value for each attribute of its type e g for each person there must be a name Relationships on the other hand model connections between things For instance a book may be on loan or have been lent to a person or not Also relationships have a type and may have attributes for instance the start and end date of the lent An entity relationship schema is a directed graph whose nodes are entity types and whose arcs are relationship types In other words a schema is given by a set of entity types and a set of relationship types where each relationship type is assigned a source entity type and a target entity type In our example the set of entity types is person subscriber book whereas the set of relationship types is loan The relation
116. preads and eggs in finite projective spaces b Foundations of logic and mathematics by Y Nievergelt Shadows of the mind by R Penrose Error coding for engineers by A Houghton Mathematics of information and coding by T S Han and K Kobayashi Rudiments of mu calculus by A Arnold and D Niwinski lAsymptotics and Mellin Barnes integrals by R B Paris and D Kaminski Impulsive control theory by T Yang Geometry of pseudo Finsler submanifolds by A Bejancu and H R Farran Fuzzy logic by G Gerla Dej lt j gt gt gt 135735 _Newitem Modify Delete Author Title Enable filter Clear filter ee Figure 1 An ERW list where you can choose books You can browse around and filter elements to be true the filter shown has been customised Once you find to the book you want to edit you get to a form looking like this v Book Algebraische Grundlagen der Informatik by K U Witt Mozilla OK Apply Apply amp Clone Cancel Title Algebraische Grundlagen der Informa Author K U Witt Publisher Vieweg ISBN Code Year Description Browse Send p Lentto Long term 01 02 2002 S Bek ong term 02 05 2001 del lt lt lt gt gt gt if 1 3 7 3 Remove Startdate f 2002 Enddate fa 42902 Type longterm z Reset Apply Jonathan Aaronson Emile H L Aarts Khaled A S Abdel Ghaffar Ulrich Abe
117. previous version if the original publisher of that version gives permission List on the Title Page as authors one or more persons or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal authors of the Document all of its principal authors if it has less than five e State on the Title page the name of the publisher of the Modified Version as the publisher Preserve all the copyright notices of the Document Add an appropriate copyright notice for your modifications adjacent to the other copyright notices Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below e Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice Include an unaltered copy of this License Preserve the section entitled History and its title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If there is no section entitled History in the Document create one stating the title year authors and publisher of the Document as given on its Title Page then add an item describing the Modified Version as stated in the previous sentence Preserve the network location
118. quires a completely different approach as the state of input controls is not sufficient to store this information ERW uses JavaScript scripting and the W3C DOM to alter the appearance of the form showing how relationships are added or deleted and how their attributes are mod ified All these data are stored in the JavaScript state of the browser Suitable JavaScript code interacts with the database presenting the user with a modified view which however does not really exist server side When the user has finished with editing and submits the form the entire JavaScript state of the form is suitably serialised and sent to the server The PHP run time environment on the server locks the part of the database that is affected by the changes checks that no integrity constraints are violated and performs the changes If anything goes wrong the user is presented again with the form that was submitted using the serialised client state the server is indeed able to completely rebuild the JavaScript state of the submitted form Simulating Remote Procedure Calls JavaScript provides no direct way to connect to a database Usually whenever the user has to choose among a set of elements the entire set is packed in a suitable HTML input element e g SELECT and sent to the browser This approach however makes it impossible to edit large databases ERW aims at the greatest generality and thus implements on top of HTTP a simulated remote
119. ray unquote string Undoes what EWR quote did but works by value query query Executes the given query and returns the result Database errors cause logging and immediate exit select select query It is identical to ERW query but it automatically prefixes its argument with SELECT so you can write things like ERW select from type getRow select query It is identical to ERW select but it automatically returns the first row of the result set 73 Chapter 10 Useful Functions ERW getOne select query It is identical to ERW getRow but it automatically returns the first column of the row Very useful when you just want a single datum from the database JavaScript Functions 74 To use these function you must know some convention about the HTML elements identifiers generated by ERW This is necessary as to create useful hooks you need to be able to detect which row of a table the user selected Each relevant HTML element in a page generated by ERW has a well defined identi fier In particular whenever a list of elements is displayed to the user the correspond ing table has an identifier in the XML sense generated by prefixing a letter followed by the underscore character to a table name More precisely e main lists are named m type in the editing of relationships the list that lets the user choose entities is named s_relat
120. relation ship with attributes can be edited Embedded entities will be created or deleted following the user editing This approach has a major limit you can only edit attributes of the embedded entity and not relationships Thus in particular no total relationship can go out of the embedded entity On the contrary using the rlw type one gets a new form to fill for a new weak entity The form can modify of course its relationships However the new ele ment is actually created and associated to the owner Note that because of this difference it is not possible to associate a new weak entity to a new entity i e to an entity that has not been written to the database The user will be requested to save the current changes to the database to continue rN The type of a non absorbed relationship type The user is presented with a set of input elements that allow one to create a relationship and modify its attributes A particular case to handle with care is that of loops A relationship type can have the same source and target e g father of and in this case for absorbed relationship types you must choose one direction for editing non absorbed relationship types can only be edited forward There is however a special important case when you define a relationship type be tween entity types with a common subtype it is treated as a loop as indeed you can associate entities of the common subtype to entities of the same type In
121. remely flex ible as essentially anything can be implemented on top of the skeleton if sufficient documentation is available it is also very dangerous Usually procedurally speci fied customisations end up being strongly tied to a specification at that point deep modifications to the specification lead to unpredictable behaviour ERW adopt a design pattern that we term specification percolation the generation of the user interface is akin a fluid percolating from the ERL specification to the user interface through a series of additional specifications which act similarly to active membranes they may filter some information and even replace it with something else but it should almost never happen that information is lost in the process or an inconsistent configuration is generated More down to earth customisation of ERW is a process by which you can alter cer tain standard choices made by ERtool when producing the definition files create custom forms and add external code to the ERW standard database processing code so to perform special actions Layouts A SQL er spec Docs by I Custom files f s Figure 4 1 Specification percolation In Figure 4 1 we represent schematically the way information percolates through ERW s additional specifications The first membrane on the route of this information to the user interface is locali sation using the standard GNU ge
122. representing references to other tables If you use too long identifiers this construction could yield names that exceed the maximum identifier length in your database Try to use short meaningful identifiers All attributes have an ERL type ERL types include the following SQL types CHARACTER CHARACTER LARGE OBJECT CHAR CLOB CHARACTER VARYING NUMERIC CHAR VARYING DECIMAL VARCHAR DEC NATIONAL CHARACTER INTEGER NCHAR INT NATIONAL CHAR SMALLINT NATIONAL CHARACTER VARYING DATE NCHAR VARYING TIME Moreover there is an additional simulated type BOOLEAN which holds a truth 9 Chapter 2 ERL an Entity Relationship Language value and TEXT which is a non SQL but largely diffused variant of CLOB All SQL types are faithfully preserved during reification whereas BOOLEAN is mapped to CHAR 1 the column will hold 0 or 17 Finally there are two virtual types enum and fset They were added to increase the expressive power of an entity relationship schema described in ERL and avoid the creation of many relationship types with the sole purpose of simulating data types The enum type Often in databases one has to store one out of a finite set of values These values may be fixed forever e g weekdays male female or could vary over time e g positions in a company To this purpose ERW provides two solutions by means of the enum type and of the enum element The enum element specifies an SOL type a
123. resulting string will be printed using the given alignment width ecc essentially the string will be formatted with a directive obtained by stripping the separator and whatever follows and appending s As an example SD book display fmtString s Ss s SD book display field array title author loan_person gt lname Chapter 4 Customisation would display a book by appending to the title and author the list separated by commas of the people that borrowed the book note however that in this case you could get doubles if the same person borrowed many times the same book Tabular Displays Sometimes you could prefer a rigidly aligned tabular display in which each field oc cupies a fixed amount of space This is easy to obtain using printf s sophisticated field width and alignment control However you will also need a fixed width font and a table header specifying the name of the columns To obtain this effect you can set the variable D type display head to any string Virtual Attributes When building labels sometimes you can use virtual attributes which do not really exist in the database but are generated at run time These are the currently imple mented virtual types MIMEtype Only for filesets contains the MIME type of the file it is derived from the file name extension original Only for filesets contains the original filename if you are using or
124. s are specified in ERW as in RFC 2616 for the Accept Language HTTP header that is a two letter language code a hyphen and a two letter country code Thus it IT is the Italian spoken in Italy whereas en UK is British English If you want to support some languages you must specify them in the _ERW_supportedLocales configuration variable Then for each language you have to provide a file that for each string used in ERW provides a translation An example of such a file for Italian is given in the file ERW it po that comes with the distribution You should write a similar file for your language and possibly send it to me compile it using the msgfmt utility coming with gettext and finally installing the resulting ERW mo file in the proper directory e g it LC_MESSAGES for Italian inside the path specified by the _ERW_localePath configuration variable Then ERW will fetch from the browser the preferred language and try to match it with one of those supported You can also set a default locale instead of en us or a fixed locale see Chapter 7 The translation file above accounts for all strings built into ERW However you may want to translate other parts of the user interface such as labels enumerative types and help attributes This is possible simply by creating translation files named ERW id labels ERW id displays ERW id enums and ERW id help where idis the identifier of the root element of your ERL file e g
125. sesesesecsseseessesesess 75 UTE 8 SuppoOtt 2 2 Enden rrr Hr hiis ci sr i e E c PU ecl da 75 12 Script Reference eese esses ete tenete sten tnn then setenta ens nste tatnen sete tnn 77 ERW checkERWphpusreus e cess ceteri cese eet rente gea eade uir sein eedem e deoa Tes ee edes bees 77 ERW checkdbspbgoucs cu exeeeetesecuncecusgsubes etse ev uo eee ches EEE vus EUM noe nune EAE EEEE 77 nii ole EE 77 DAIS AP Iles acts rM 77 MEO TET asf E E E A snes saevsdes sass T E 77 decau lEs PAD rres a ein xs ena ETENEE se inu a NR o NEE eX SURE sunpeesascsuns se ape nde Po PEN ORE 78 CNOWI iD MD MM E 78 SSCP US Sts PNP cress EU Tu MERI I 78 13 Troubleshooting ssis 79 EREGOL problems eine p D Ree Ra OR ania amen es 79 PHP problems MS 79 sejusduac 79 Configuration and Customisation Problems sess 79 When Nothing Seems to Work eee nennen 79 Reporting BUGS au niieinsa neatis need Ue tech ior nieder 80 A GNU Free Documentation License cccsssscssccsssssssccsssssssscsssssscecccsssesecsessesseesees 81 Pr amble 2 necatta Ste Pre 0 Cnr Oa SEP ete dde cds 81 Applicability and Definitions ssssssssesseeeeeeeneee een nnne 81 Verbatim Copying is ssccscsssssncescvesesnssacveseststecssscvessssteyecssussesescscpasestotscvanesnavsssepestabesscnecee 82 Copying in Quantity iat anasasea cer irn cto
126. ship type 1oan has source entity type person and target entity type book An instance of an entity relationship schema is a sort of abstract database It is given by a set for each entity type called an entity set and a multirelatior for each relation ship type Not surprisingly elements of the set associated to an entity type are called entities and elements of the multirelation associated to a relationship type are called relationships A multirelation is an extension of the mathematical concept of relation in a mul tirelation from a set X to a set Y two elements can be in relation more than once Mathematically a multirelation from the set X to the set Y is a set R the support of the multirelation equipped with two legs that is two functions R R X and R R Y A multirelation should be interpreted as follows if there is an element r of R such that R r x and R r y then x and y are related once But if there is another element s of R such as K s and R s y then x and y are related twice and so on If there are no elements of X and Y that are related twice then R is a standard relation It will be useful in the following to note that given a multirelation R from X to Y we can build a multirelation RT called the transpose of R going from Y to X simply exchanging the r le of R and R Getting back to entity relationship schema instances we note that if a relationship type goes from an entity type instan
127. sing Filters senem era arret eere pe He FI P SEEE eaa 33 FOO MS eM RM EHE 35 The Lock HOOK ccce treten tiet teet beret tier La 36 Th Pre update HooK tette ette eere tiae ieget 36 The Post update Hook iiie rese tee eee pre P E edens 37 The Deletion HOOKS sissies ttt te teet eer e E cerent 38 The Post Authorisation Hook eseseeeeeeeeeeeenn eene 38 The Selection load Hook essere nennen 39 The Button Hook acer rese te naa ieee 39 The Button Inhibition Hook eene ener nnne 41 The Form Loading Hook 41 CUSTOM POfitisiie iet eco rr Ai ances I EE A RR asec enna eet eas 41 POLI Resolu tiori err rte secs tenet eer rica e rape ee enun era 42 ERF an Entity Relationship Form Language sese 42 iii 5 Authentication and Authorisation ccccccccssscssssscssssscssssscssssscsssscssssssssssssssescssseees 47 Custom Authentication cccccccccccccccesccccsssececsscesssescssseccsesscesssceessseeesesecseesseseeecesess 47 The Authorisation SysStenN sesidir sentesi en ERa E EE TERR nennen nennen 47 Changing OWNER sia tiet ieii einai erae EEEn tei E Aana iae arike Ee 48 The Selection Level Turing tnter entera 49 Restrictions on Element Based Authorisation c cccccccsesscesssessseeseecseeeseensees 49 6 Transaction Support eese esee tete ste tete teta tasse inta ense etn tn en sne te tntnnn 51 7 Installation
128. sis A relationship models a connection of some kind between entities The rel element describes a relationship type It must contain two 1eg elements and any number of attr elements The first leg is taken to be the source of the relationship type and the second leg its target 17 Chapter 2 ERL an Entity Relationship Language Notes 18 Attributes id A restricted identifier for this relationship type label A label for this relationship type The user will be always presented this label when dealing with the relationship type abstractly i e without starting from an entity type absorbable This field can be set to true the default or false In the second case ERtool will always generate a support table to reify the type Reification The reification techniques used by ERtool have been described in the Section called Reification in Chapter 1 Here we dwell into the details of field naming and so on First of all not all cardinality constraints are supported by ERW if on both legs the upper bound is 1 then at least one leg must have a lower bound 0 Bijections which are discarded by this restriction are useless as they make it impossible to modify locally the database A nonabsorbed relation with source and target entities A and 8 respectively gets two additional columns id0 Aand id1_s that are used to point at the elements of the two entities by means of the id column in other words they give t
129. spose is Note If you look back carefully you will notice that the cardinality constraints of a re lationship type associated to the source and target entity types are really expressed in terms of the legs of multirelations indeed cardinality constraints have nothing to do with the entity types they are a purely set theoretical feature of the multirelations instantiating a relationship type One could equivalently say that a constraint of the form x 1 forces the corresponding leg to be an injective function and that a constraint of the form 1 x forces the corresponding leg to be an surjective function this definition is equivalent to the one above All in all noting that a monodrome total relation is commonly called a function we have the following table assigning standard mathematical term to the cardinality con straints specified on the source entity types rows and on the target entity types columns 0 1 121 0 N 1 N 0 M 1 M 0 1 injective injective partial surjective partial and function partial function surjective function partial function 1 1 injective injective function surjective function and function surjective function Chapter 1 Overall System Design 0 N injective injective relation surjective relation and relation surjective relation 1 N injective injective total total and total and relation _ surjective relation surjecti
130. stom forms ERL Types vs ERW Types When you create an ERL file you specify an ERL type for each attribute This type is automatically mapped by ERtool on an ERW type which specifies the user inter face for that attribute Moreover an ERW type is assigned to each relationship type incident to an entity type In the following table you can find the correspondence between ERL types relation ships and ERW types the types that ERtoo1 assigns by default are marked with an asterisk CHARACTER CHAR CHARACTER t a fa ha pw VARYING CHAR VARYING VARCHAR NATIONAL CHARACTER NCHAR NATIONAL CHAR NATIONAL CHARACTER VARYING NCHAR VARYING CHARACTER LARGE OBJECT CLOB a fa ha t pw TEXT TEXT a INTEGER INT SMALLINT ip NUMERIC DECIMAL DEC ne ns ENUM dynamic e ENUM static sr BOOLEAN b DATE d jd TIME h FSET f absorbed relationship types r1 ris transpose of absorbed relationship types rit transpose of identification functions for riw rle weak entities non absorbed relationship types rN The most common type a string of text The user is prevented from inserting more characters than the SQL field can store pw As above but the input field is obscured the user just sees asterisks while typ ing Useful for passwords a fa ha A fairly large amount of text currently limited to 64KiB displayed in an HTML TEXTAREA element The user has the possibility to upl
131. t by the Free Software Foundation 1 http www gnu org copyleft 85 Appendix A GNU Free Documentation License 86
132. tandard methods on it or you can directly use ERW s internal versions Note that usually accessing types not owned by the current entity could give rise to a database error ERW_userld The id of type usr corresponding to the current user or 0 if no user has been authenticated or if the authenticated user is not in usr _ERW_auth An associative array with keys select update insert and delete that describe the current permissions ERW locale The locale that has been negotiated with the browser ERW lang The language part the first two letters of the locale that has been negotiated with the browser Note again that you can access local copies of these variables under the names db SuserId and so on The Lock Hook The lock hook is used during database update and deletion phases It is set by as signing to the variable D type lock an array containing the names of tables that must be locked together with the neighbourhood of the current entity It allows you to set up things so that you can atomically check and possibly update your own support tables during an atomic ERW transaction The Pre update Hook The pre update hook is called before actually updating the content of a row or in serting a new row It is set by assigning to the variable D type preUpdate the name of a PHP file Note that the file is relative to the server directory where PHP scripts are installed If it exists the file is inc
133. tandard one The label is specified using the usual keys fmt String and field but preceded by the key chain D type display relationship type_other entity type For instance SD book display regards_edition fmtString s d SD book display regards_edition field array publisher year will list editions in the form of a book just by their publisher and year we are assuming that the identification function going from edition to book is named regards and that edition has attributes named publisher and year Ordering Elements By default entities and relationships are ordered with respect to their identifier this however is not very meaningful You can specify the display order of entities and relationships by setting the variable D type orderBy to a string containing an SQL order by like order specification a list of comma separated attribute specifiers possibly followed by asc or desc for ascending or descending order For instance SD book orderBy book author book title would order books by author and title in ascending order Instead SD loan orderBy loan startdate desc would put in front the most recent loans and SD subscriber orderBy person lname would order subscribers by last name Note that you cannot order absorbed relationship types and that you cannot use non monodrome relationship types in an order specification in
134. the current authorisation array computed by ERW The latter associates a boolean val ues to the keys select update insert and delete each value specifies whether the corresponding privilege is granted for the current element or type Moreover it associates a string to the keys selectDenied updateDenied insertDenied and deleteDenied the string is the error message produced when the corresponding privilege is denied Note that in the case of a denied update privilege in the pres ence of select privileges the message will be displayed but the user will be anyway presented with a read only form Moreover an empty string will cause no error mes sage to be displayed You can modify the defaults for these messages by modifying a suitable configuration variable Chapter 4 Customisation During the execution of the post authorisation hook you can just assume that the given type and all authorisation related tables are locked Queries outside this set could give rise to an error Example 4 2 Old book entries cannot be modified In our library books older than 1950 have read only entries their data cannot be modified and they cannot be lent To obtain this effect we can just check the publica tion year in a post authorisation hook and clear the update privileges in a file named bookPostAuth php lt php if ERW getOne year from book where id Sarg id lt 1950 Sarg auth update false Sarg auth updateDeni
135. the PHP main configuration file the setting will have no effect ERW php This script contains all of the common code list php This script creates a main list that is a list of entities of a given type and provides buttons to modify them Its only parameter is t ype the name of an entity relationship or dynamic enumerative type 77 Chapter 12 Script Reference form php This script creates a form to edit an entity Its parameters are type the name of an entity relationship or dynamic enumerative type and id which provides the SQL identifier of the element to edit if it is zero a new element will be created default php This script generates the CSS style sheet used by all other scripts It can be tweaked to suit your needs chown php This script allows to change the owner and the group of an element It has the same parameters as form php setprefs php This script allows the user to change some preferences including font size and the number of columns rows of editing elements It has no parameters as it will simply try to set a cookie 78 Chapter 13 Troubleshooting As for any web application troubleshooting a ERW installation is not easy Many components must collaborate correctly HTTP server DBMS etc to get everything working and diagnosing which component caused the failure is often difficult Some of the most sophisticated scripts for instance are loaded in hidden frames and see
136. the Section called Caching in Chapter 3 ERW supportedLocales A PHP array of locales for which translations are available HTTP language ne gotiation will be used to select the most appropriate one This variable defaults to array en US ERW will try to match the locale requested by the browser with one of the sup ported ones As a last resort it will use a country specific language such as en US for a generic language such as en Thus the order in the array is impor tant if you specify array en UK en US upon a generic request for en the user will get the en UK locale ERW fileBasePath An absolute path indicating the directory where all files relative to the database are stored A hierarchy of subdirectories one for each entity and then one for each fileset will be created automatically when files are uploaded Important This directory and its subdirectories must be writable by the user under which Apache runs usually apache Or nobody ERW authenticate The name of a PHP file containing code for custom authentication See Chapter 5 ERW globalPrivileges A conjunction of the bit masks ERW SELECT ERW UPDATE ERW INSERT and ERW DELETE that gives the global puc The default value is ERW SELECT ERW UPDATE ERW INSERT ERW DELETE ie all privileges to everybody See the Section called The Authorisation Bust in Chapter 5
137. tiated in a set X to an entity type instantiated in a set Y then the multirelation instantiating it must go from X to Y In our example an instance of the database specifies a set of persons a set of sub scribers a set of books and a multirelation for loans Each loan i e each element of the support of the multirelation has an assigned person and book and of course the same person can borrow the same book several times so we really need a mul tirelation Finally an instance of an entity relationship schema specifies for each entity set and multirelation a function that assigns to each element its attributes A precise defini tion of this function would require a precise definition of the attributes and of their Cartesian products and it is beyond the scope of this section Chapter 1 Overall System Design Getting it all together entity relationship schemata are a syntax that allows you to model some real world objects and their connections Each schema has however a semantics its instances The purpose of a database managed by ERW is to store an instance of an entity relationship schema and let the user modify it Important The discussion above may have bored some reader but it is necessary be cause ERW implements on the top of a standard SQL database the multirelational se mantics of entity relationship schemata described in Multirelational Semantics for Ex tended Entity Relationship Schemata With Applications Pr
138. tion to organise authorisation information In particular for each user you can specify a primary group which plays a special rA le Then the entity type type is used to set up authorisations Each entity in type has a name which should be the name of an entity relationship or dynamic enumera tive type If a type is not listed in type then everyone can do with it whatever is granted by the global privileges which by default are all but this can be changed in the configuration file As soon as a type is entered into t ype however it becomes ac cessible onl id pecified users y to the specified users and groups it is easy to forget to register a type in type however there is a script that can do the check for you For each type you can separately specify globally or on a user group basis select update insert and delete privileges Users holding select privileges can list and inspect elements of a given type users holding update privileges can modify elements of that type users with insert privileges can add new elements of that type users with delete privileges can delete elements of that type As explained in the definition of the ent element you can specify that you want each entity of certain type to have an owner and a group that is that you want element based authorisation In this case the owner of an entity has some additional privileges on the entity even if there are no global privileges More precisely wh
139. to specify that an area of text should get a WYSIWYG editor Note that presently HTMLArea works only on Gecko based browsers and Explorer in all other supported browsers the effect will be the same as that of a First of all you must download and install HTMLArea 3 or higher and set a suitable configuration variable Then there are several ways to customise HTMLArea For the time being configuration is common to all instances and contained in the file js htmlAreaConfig js in the document root The code contained therein is evaluated immediately after loading HTMLArea technically before calling HTMLArea init and must assign to the variable htmlAreaConfiga function returning an HTMLArea configuration object Finally the configuration object can contain an optional erwPlugins field which must be an array containing the names of the plugins you want to register in each HTMLArea instance it is your responsibility to load those plugins For more information have a look at the HTMLArea documentation As an example the sample file provided with ERW loads some plugins and then just makes the background white Note that is essential that plugins are loaded before HTMLArea init whereas they must be registered after the creation of an HTM LArea editor var erwPlugins TableOperations ContextMenu CharacterMap 57 Chapter 7 Installation and Configuration for var i in erwPlugins HTMLArea loadPlugin erwPlugins i htm
140. tomised The same holds for labels of relationships with attributes The array controlling the label of an element is D type display More precisely S D type display fmtString must be a printf like format string it must be interpreted by PHP whereas D type display field must be an array of attribute specifiers and constant strings whose values will be used together with the format string Of course the number of elements of 29 Chapter 4 Customisation 30 D type display field must match the number of format specifiers in the format string Certain data such as enumerative type or thousand separated digits are automati cally formatted in the same way they would be presented to users in forms In this cases you should always use a s directive in the format string The d directive can be used only with nonformatted numeric types Note ERW is usually able to distinguish whether a string is a constant or an SQL specifier In case it gets confused just start your constant string with the quote will not be printed but ERW will know that you meant literally what follows Format String Extensions The format string supports two useful extensions which have been thought to handle the case of NULLValues and multiple value attribute specifiers If a directive has a just after then the directive is optional If the associated pa rameter is empty or NULL then the directive the preceding
141. tp www fckeditor net 3 http www dynarch com projects calendar 59 Chapter 7 Installation and Configuration 60 Chapter 8 ERtool The first component of ERW you will have to deal with is ERtool which is re sponsible for analysing ERL files checking the consistency of the entity relationship schemata they describe and produce various outputs depending on the options you specified ERtool is a Java version 1 4 or greater application and as such comes in the form of a Java archive a file containing a number of Java classes in compressed form The Java archive of ERW is not surprisingly named erw jar When you want to recall ERtool you must be sure that the archive is installed in the extension directory or that you provide suitable options to Java or that you set the CLASSPATH environ ment variable so that it can find the class Said that ERtoo1 is a Java class whose complete path is it unimi dsi erw ERtool Thus you can invoke it with java it unimi dsi erw ERtool filename since it expects to read an ERL file from standard input The archive erw jar contains also a Java manifest that allows you to run ERtool just with java jar erw jar filename As a commodity a command named ertool a script shell that invokes the Java class is also provided It takes the same arguments as the Java class After searching for the ERL DTD in the current directory ERtool looks in usr share ERW dtd and f
142. ttext package labels for attributes and enumer ative type values are translated in a suitable language usually negotiated with the browser Localisation is discussed in Chapter 11 23 Chapter 4 Customisation Then the administrator may set up custom files which alter in a controlled way the information represented in the definition files This modifications may range from filtering options specifying which fields are important to find quickly entities and relationship of a given type labelling print like formatting strings that use the attributes of the schema and alternate user interfaces This information allows to tune several parts of the application but it is not necessary to specify any part of it for instance filtering is performed by default on the first mandatory attribute and labelling is handled analogously Then the user may specify custom forms These are completely redefined forms which are described in ERF an XHTML like language that contains the basic ele ments plus suitable elements to position the input controls for attributes and rela tions Of course forms must satisfy some constraints for instance they must contain all mandatory attributes but this is checked automatically Again specifying a custom form is not necessary ERW is able to generate autonomously a default form using customised filtering options alternate user interface and so on Of course these may be all re specified at the
143. uage vii Preface ERW gives you for free user group and element based authorisation Select up date insert and delete privileges can be set up separately e ERW is based on a subset of SQL 99 that will work on almost every DBMS and uses the PEAR database abstraction layer so you are not bound to a particular choice of DBMS e ERW uses ERL to define additional data types such as enums that are not avail able in SQL 99 and maps them to standard types ERW provides filesets that is set of files with attributes that are related to an entity This allows to easily add to the database multimedia data stored in the filesystem There are of course also some drawbacks ERW makes a number of assumptions on the structure of the database and on the inner workings of your entity relationship schema that prevents you from doing certain things ERW is based on local editing each entity has a corresponding editing form and from that form you can edit that entity and adjacent relationships but you cannot edit other components of your entity relationship schema you can of course from their respective forms ERW uses a conservative approach in deletions whenever an element is deleted all incident relations are also deleted unless this would break logical integrity in which case the deletion cannot be performed This is in contrast with the cascading approach in which the deletion of an element can cause deletions of ot
144. ude the original English version of this License In case of a disagreement between the translation and the original English version of this License the original English version will prevail Termination You may not copy modify sublicense or distribute the Document except as expressly provided for under this License Any other attempt to copy modify sublicense or distribute the Document is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance Future Revisions of This Licence Notes The Free Software Foundation may publish new revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns See http www gnu org copyleft Each version of the License is given a distinguishing version number If the Docu ment specifies that a particular numbered version of this License or any later ver sion applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has been published not as a draft by the Free Software Foundation If the Document does not specify a version number of this License you may choose any version ever published not as a draf
145. utes into their sources if it is possible then it checks whether it would be possible to absorb the remaining relationship types without at tributes into their targets and complains if this is true as by design absorption is pos sible only in the source entity types finally it creates a support table for all remaining types There is some control on the first part of the process as you can explicitly ask for a relationship type not to be absorbed even if it is possible Subtypes are realised by keeping in sync the id fields of the tables reifying the types involved Thus for instance if A is a B then for each value of the id field in the table reifying A there is a corresponding row of B whose id field has the same value This behaviour mimics exactly set theoretical inclusion Note The reification process is more complicated as for instance part of the reification of a dynamic enumerative attribute consist in creating an ad hoc table for storing the enumeration The details of the reification process are given for each ERL element in detail in Chapter 2 In any case ERtool generates detailed documentation about the reification process Concurrency ERW is able to coordinate any number of users accessing concurrently a database The design principle guiding the handling of concurrency is very simple but effec tive since editing is local ERW keeps track of all changes made by the user in the browser When the user submits its chan
146. ve relation total relation 0 M multirelatigsurjective multirela tion 1 M total mul total tirelation surjective multirela tion The empty places represent impossible combinations Note that if you exchange the two pairs of indices you obtain the cardinality constraints on the transpose of the multirelation Thus if a multirelation has to be an injective relation its transpose has to be a partial function and viceversa Weak Entities A weak entity is an entity that exists only if is related to a set of uniquely determined entities which are called the owners of the weak entity For instance we could extend our library with a weak entity type edition each book has several editions and certainly it is nonsense to speak about an edition if this does not happen in the context of a specific book From a user interface viewpoint weak entities are usually edited in the context of one of their owners When an entity is deleted from a schema instance all owned weak entities are deleted too We shall call the type of a weak entity a weak entity type For entities of type w to be owned by entities of type x a requirement must be sat isfied there must be an identifying function from w to x that specifies the owner of each entity of type w that is a relationship type going from w to x whose cardinality constraint impose its instances to be functions Deletion of an entity of type x implies deletion of
147. which would be valued NULL Moreover if you start from a relationship type you may want to move to its source or target entity type this is the rA le of leg codomain which must be of the form ent ity type_leg index for an example see the Section called Displaying Relationships 27 Chapter 4 Customisation Thus for instance you can access the name of a subscriber with person name here person is a qualifier or the name of the book a loan refers to with book_1 title here book 1 is a 1eg codomain Of course specifying a 1eg codomain when the start ing type is not a relationship type will give rise to an error There is also an attribute id that exists in every type and it is guaranteed to provide a positive distinct number for every element of a given type Following Identification Functions More interestingly we can access attributes of related entities e g owner entities using the relationship type attribute notation the relationship type must be named as an ERW attribute e g 10an book You can chain more than one relationship type of course the target of a relationship type in the chain must be a subtype of the source of the following one Note again that you may need to add a qualifier at the end of such a chain if the attribute your are interested in belongs to a supertype of the target of the last relationship type of the chain Let us build an artificial but complete example using supertypes and identi
148. y from the GraphViz suite of tools More details can be found in the Section called The DOT graphical back end il8ntype Activates the internationalisation back end The output is a gettext template file that contains all the attributes and leg labels if type is labe1 all the labels of static enumerative types if type is enum or all the help strings if type is help The file can be then used for translations or manipulated with standard gettext commands See Chapter 11 ERtool performs a number of checks to ensure that your entity relationship schema is sensible that it respect the limitations of the run time environment and that it does not contains cardinality constraints so strict that they would make modifications to the database impossible Most of the error messages are self explanatory but some explanation is necessary about cardinality constraints Recall that an entity relationship schema is a directed graph Thus it makes sense to speak of directed cycles sequences of contiguous arcs with the right direction that form a cycle The first check performed by 1 ERtool is that no such cycle is formed by total injective relationship types In such a case it is impossible to modify the database using only local modifications that is us ing ERW as all entity sets along the cycle are forced to have the same cardinality In this case ERtoo1 will stop with an error Chapter 8 ERtool Then ERto
149. ybe some custom button should make them able to print data about them but we do not want to confuse them with other buttons This can be obtained by adding the following to the customisation file for the entity book SD book inhibit list new true SD book inhibit list modify true SD book inhibit list delete true Note that using t rue as a value is purely incidental any other logically true value would have done the job The Form Loading Hook When creating a form for editing ERW must decide whether it is the case to provide the user with a custom form The chosen custom form depends on a key by default the name of the type of the element which however can be set depending say on the user using the form loading hook The form loading hook is activated by assigning to the variable D type loadForm the name of a PHP file the string returned by the file will be used as a key to load the form see the Section called Form Resolution Custom Forms Custom files are very useful but they cannot for instance change the order in which elements are displayed Custom forms instead are a much powerful feature that al lows to structure freely ERW s editing forms 41 Chapter 4 Customisation 42 A custom form is defined by an XML document in ERF Once the form has been cre ated it must be compiled using ERtoo1 and the resulting PHP file must be installed in the custom
150. you can really know what it s doing Assuming that you installed ERW correctly which includes configuring PHP and Apache you now have to generate the definition files these are PHP files that contains information about the database They are essentially a reworking of the data contained in the original ERL file The definition files are read by the PHP scripts of ERW s run time environment to produce the actual forms Definitions files are again generated by ERtoo1 using the ERL file and should be moved ina place where the run time environment can find them to this purpose there is a configuration variable that can be set Other configuration variables let you choose the type of DBMS localisation fea tures and so on Once everything is set up your are ready to edit the database You should provide a method to access the editing scripts with the right URL A sample file index orig php can be used as a first try There are however several things that you could not like in the forms thus created For instance if you have a two elements enumerative type say male or female you could prefer a radio button to a drop down menu Or you could not like the way an element is labelled by default using its first attribute For such things ERW lets you write custom files which alter some of the data of the definition files so to tune the user interface to your needs Custom files also allow you to implant hooks in the ru

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