Lazy User's Manual and Reference
Contents
1. html purexml purehtml J node_def end node_def node node_identifier parameters cachesize number content from_part A node schema has a name and a possibly emtpy list of parameters The from select and order parts determine the list of database tuples to represent in an instance of this node The fields de fine the representation of each tuple and the links to other nodes parameters parameter parameter parameter identifier identifier letter letter_or_digit _ content field field field href expand link field field include link active href active link field list set_attribute_or_variable on_action content A field is either the source anchor of a possibly active reference link or the result of including some other node instance at that place or a content element and XML or HTML element with embedded elements The fields that appear in the source anchor of an active link can set attribute values and define action to undertake when the link is activated field_list field field content element type field field simple_expression gn field F field ki A content element is either a typed element made of one or more subfields or a simple expres sion A content element surrounded by and y is evaluated for each selected tuple Only one2. admin Lazy source code of the interactive development and administration hyperspace bin scripts to start and manage the Lazy system doc documentation examples example hyperspaces hsqldb the hsql database engine http hsqldb sourceforge net with a demo directory that contains the data of the example Web site sre the Lazy source code tomcat part of the tomcat servlet container from the Apache Jakartaproject http jakarta apache org webapps lazy contains the lazy web application including the lazy node server servlet NOTE If you already have a tomcat server on your machine copy tomcat webapps lazy to the webapps directory of your tomcat server and restart tomcat 1f required 2 3 Starting the Lazy system with the example application Lazy comes with an example web application for a virtual museum It is comprised of a small database that stores information about works artists exhibition etc and a set of hypertext nodes dynamically generated Web pages to navigate and update the museum Step 1 Set environment variables Before running the Lazy system on the example database you must define the following envi ronment variables LAZY HOME the installation directory of your Lazy system the full path of your lazy x y directory JAVA_HOME your java installation home TOMCAT_HOME the home directory of your Tomcat server set it to SLAZY_HOME tomcat to use the server that comes with Lazy Then you must
3. a name under which somebody can connect to a Lazy server By default the username PUBLIC is used when opening a Lazy session A user can be defined as administrator In this case she will have full access to every node and data Datagroup a symbolic name for a set of data in a database A tuple in a table may belong to zero or one data group thus the same table can hold data belonging to different applications For instance a single database can be used to manage different museums The datagroup of a tuple is indicated by the value of an attribute reserved for this purpose When loging in a user can select a datagroup otherwise she will work in her default datagroup Role a role represents a set of access rights to nodes and database tables For instance role VISITOR can accees the node MUSEUM artist index while role CURATOR can access MU SEUM update_catalog etc An access right is thus a pair role project node or role table The wildcard form project means all the nodes of this project The main advantage of roles is to avoid defining the access rights of each user in each datagroup see grant Grant when connecting a user is granted a set of roles These roles depend on the datagroup she chose to work in So for instance user JOE could have role VISITOR in the MU SEUM_OF_MODERN_ART datagroup and roles VISITOR and CURATOR in CITY_MUSEUM A grant is thus a triple user datagroup role If datagroup is it means
4. 1 on Go do navigate node Works with name w select works whose title contain w and show them at the specified level of detail title si y include W Description detail from works selected by title like concat concat w 6 13 Internationalized strings To be written 7 Managing projects 7 1 Projects A project is mechanism to group a set of node schema that have a common purpose It is similar to a module in a programming language The IDE has an environment to manage project create new projects delete them add update and delete nodes in a project Every project has a set of properties that are inherited by all its nodes a database connection formatting files CSS XSL background image a default node type HTML or XML The full name of a node n belonging to project p is p n When refered from a node of the same project the p prefix can be omitted 7 2 Connections A database connection is a JDBC connection it is comprised of a database URL a JDBC driver a class name a username and a password With different projects connected to different data bases it is possible to build a single Lazy interface that federates several databases After creating a new connection with the Admin gt Connection interface it is necessary to reini tialization all connections in order to activate this connection A reinitialization is also required when some database connection has been lost due to a n
5. expressions in the selection of expressions of the node schemas 4 4 Examples The following node schema presents information about a work of art It uses a one row and two column table The first column td presents textual information and the second one displays a picture of the work The picture s URL is stored in the database attribute picture note how this attribute is used to give its value to the src attribute of the img element This node is based on two tables work and artist because we want to display the author s name which is not in work So we have to join the two tables with the condition work author artist ano In order to show the name of the work s owner we employ another technique which consists in including the mw_Owned node described below node mw_Work id lt table gt lt tr gt lt td gt lt h2 gt title lt p gt c_date lt p gt href mw_Artist ano name lt p gt support height x width lt p gt include mw Owned wno acquired lt p gt href mw_Works by artist ano Works by name lt td gt lt p gt lt img width 200 src picture gt lt hr gt href mw_upd Work id Update this description from work artist selected by work author artist ano and wno id The following node is simply here to display the name of a museum whose number is given as parameter Its purpose is to replace a numeric value her
6. hypertext view obtained so far enables the user to view all the information content of the da tabase However it is probably not a good hypertext in many respects In particular navigation paths can be too long to reach interconnected data In http cui unige ch isi reports design anls ahtv pdf we present of set of refinement operations that can be applied to a hypertext view to im prove its quality 5 Creating Hypertext Views on Existing Databases Lazy is aimed at creating hypertext views for existing databases There are two ways to do this depending on where you want to keep the Lazy dictionary The Lazy dictionary is a set of data base tables that store compiled node definitions project definitions access rights etc You can either continue having HSQLDB manage the Lazy dictionary in a the Hsqldb database that comes with Lazy or create a fresh Lazy dictionary in the existing database 5 1 Keeping the Lazy dictionary in the HSQL database 1 Install a JDBC driver for your database management system If your dbms has an ODBC interface e g MS Access you can use the sun jdbc odbc JdbcOdbcDriver driver that comes with the Java installation All you have to do is to create an ODBC source connected to your database Otherwise you ll find the driver either in your dbms distribution or on specific web sites The JDBC driver must visible for the Tomcat server So put it in STOMCAT HOME lib Oracle JDBC drivers for Oracle can be download
7. nodes manage projects users aceess rights connections etc This is a good test to see if your LazyCompiler properties file is correct If you forgot to modify this file the compiled nodes will be stored in the cd SLAZY HOME admin lc icon lzy Lazy node compiler 4 0b gt lt lt the url of your database gt gt project ICON connectionId DICTLAZY node maj node del node new lc node lzy lc admin lzy Optionally reload the virtual museum example The database schema data and node definitions par the museum example are located in LAZY_HOME examples museum Define the tables with mw_dbschema_ora sql or mw_dbschema_hsql sql then load the data by executing mw_data sql there are variants in Macintosh or UTF 8 coding Finally compile the museum nodes lc mw lzy lc mw contemp for hsql lzy only if using hsqldb lc mw updates hsql lzy or mw updates ora lzy Once again since SQL does not define everything different nodes had to be defined to cope with Hsqldb or Oracle or other dbms s specificities like the non automatic conversion of strings into numbers auto increment attributes sequences etc 6 Start the node server and test the installation From your Web browser open the URL http localhost 8080 lazy ns a ADMIN all and start browsing the administration and development environment 6 The language part Il 6 1 More details on the evaluation of tuple and non tuple elements The node comp
8. stored in Lazy properties as the encrypt key attribute value encrypt key lt 16 hex digits key gt encrypt off on in Lazy properties Now there is a bootstrap problem if you turn encryption on by setting the encryt off parameter to on in Lazy properties you won t be able to log in any more because the system will try do decy pher the stored passwords before comparing them to the typed passwords So you ll need to manually encrypt the ADMIN password in the secure_user database table before proceeding to the next steps This can be done by as follows Jo SLAZY HOME bin gpwd your admin password 33833A88E8F10377 your password encrypted with the Lazy key In the database update secure_users set pwd 33833A88E8F10377 where userid ADMIN Now you can log in as ADMIN an set the other user s passwords they will be encrypted 9 Language part Ill 9 1 Computing with inclusions 9 2 Java Nodes When complex computations are needed or simply functions that do not exist in SQL it is bet ter to express them in an algorithmic language rather than hack computation oriented Lazy nodes For this purpose one can define external nodes the content of which are computed by calling a Java method The name of an external node starts with two underscore characters followed by a class name and a method name The instantiation of such a node will call the corresponding method to generate a node content For instance a content el
9. such element may appear in a node definition element_type lt element_type_identifier element_attribute_identifier simple_expression tt elem_type_identifier identifier identifier element_attribute_identifier identifier identifier link include expand href href in target_identifier project_identifier node_identifier simple expression inclusion link simple expression inclusion_link A link is either an inclusion include a reference href or an expand in place expand href It refers to a target node through its identifier and a list of actual parameter values expressions The parameter values can also be obtained as the result of an inclusion active_link href project_identifier node_identifier simple expression simple expression set_attribute set attribute_identifier parameter parameter encoding function_identifier identifier input_field simple_expression Defines the value that will be affected to a tuple attribute by the next insert or update action The set parameter form is used to pass a value an expression or an input value as pa rameter to the target node In this case the active href node part must not contain parameter val ues Parameters are positional they must be given in the order defined in the target node schema A set statement automatical
10. table t set their values for the non key attributes according to what is specified in the set attr fields keyvalue keyattrident first_level_simple_expression from_part from table_identifier alias identifier table identifier alias_identifier distinct select_part group_part order_part l group part group by identifier identifier select_part selected by condition order_part order by simple_expression simple_expression condition not logical_term or logical_term logical_term logical_factor and logical_factor logical_factor simple expression comparision_op simple expression is not null comparison_op like Wel lt Mss Sa lt gt simple expression I term 4 I term term factor I factor factor stringconstant numberconstant function_identifier simple exression simple exression y table identifier attribute identifier parameter ident expression Remarks Aggregate functions min max count avg may not appear in content expressions that are re peated for each selected tuple contents within and y Content expression may not yield a boolean value because the boolean type does not exist in SQL This is not forbidden by the grammar neither checked by the compiler Boolean contents will generate ill formed SQL state
11. that triggers a database action when traversed In addition to usual elements the source anchor of an active link can have one or more input elements and must have one action element The general syntax of an active link is Active href node name parameters standard or input or action elements An action element takes one of the following forms on button label do insert table name n button label do delete table name key attributes n button label do update table name key attributes Parameter values or any expression can be used as input values as in the following node node mw add work exh e w lt h3 gt Add work title to exhibition title active href mw_Exhibition e set work w set exhibition e lt p gt Comment set org comment textarea 10 30 on Add do insert ex_content from exhibition work selected by exno e and wno w The set elements must not be confused with assignment statements The effect of a set takes place only after the corresponding active link has been followed by clicking the button Thus elements like set name Zorro The name is name Will display the value of the name attribute of the currently selected tuple not Zorro More on this in section 5 6 6 10 Designing active nodes 6 11 Pre actions 6 12 Global variables 6 12 1 System variables The Lazy node server maintains a number of system variables taht store information about the
12. DBMS to DBMS in fact SQL is only partially standardized in this respect the instantiation of a Lazy node may yield dif ferent contents depending on the underlying DBMS In particular some DBMS s try to convert strings to numbers when they appear as argument to arithmetic operators while others consider this as an error or apply string operations 6 2 Conditions and embedded queries Embedded queries are not allowed in conditions However existential conditions can be ex pressed with the following syntax exists table condition This expression is true if there is at least one tuple in table that satisfies the given condition It corresponds to the SQL expression exists select from table where condition For example the following node schema generates node instances that contain all the artists who produced at least one work before the given date d node ArtistsWithWorksBefore d lt p gt name from artist selected by exists work author artist ano and c_date lt d The existential expression can also comprise several variables An expression of the form exists table var table var condition is true if there exist tuples var in table var in table that make condition true One can express universal conditions with expressions of the form forall table condition gt condition This expression is true if all the tuples in table that satisfy condition also satisfy condition It corresp
13. In addition these actions can act on the database behind the scene without the user even noticing that his or her navigation did something on the database For instance to log the accesses to a particular node we could write the following node node record access par no contents on open insert rec table time sysdate for Oracle what par Then in another node node W include record access access to node W 6 7 Session Variables 6 8 Some design principles There are basically two ways to design active nodes 1 Design form nodes like the mw_new_Artist node above that let the user type in data in the input fields 2 Design navigation strategies to collect the requested information through navigation us ing parameter passing to transmit data from node to node The following nodes show an example of the second design alternative node mw exhibition content e display the content of exhibition e title A href mw select work e Add a Work to this exhibition from ex content work selected by exhibition e and work wno node mw select work e lt h3 gt Select a work to include in the exhibition lt dl gt lt dd gt expand href mw Work wno title href mw add work exh e wno Add from work 6 8 1 Collecting input values 6 8 2 6 9 Active Nodes and Links An active node is a node that contains active links An active link is a reference link href
14. Lazy User s Manual and Reference G Falquet May 2004 Table of contents 1 2 3 4 Tint MU CEL OM ses ccs kan cate sd e Sanscuysdens dhs oa cede ako er EEO aE SE oroS Eear ob by s k a do bas bye aen 3 Tins taal Ath nora riada ctas 4 2 1 Requirements iii ii is a 4 2 2 Downloading and installing ooonnonnncnncnncnnnncnnnnonncnnacnonononnnocnn ono nonnnn cnn onn rn nonanc ocn rn rra 4 2 3 Starting the Lazy system with the example applicatiON ococoncnnnnnnncnconnnnnnonncnnnnnncnna cnn nnno 4 Using the Node Compiler cceeessscscesceseesssseeesseesesseeecseesecsesaesesseesesaeeacsessesseeaeeassessesaeeasenseeeaes 8 3 1 With the interactive development environment eee eee eeeeeseeteeeeeeeeeeeeseeeeeeeseeaeeaseeseeens 8 3 2 In batch Mode ici nia 10 Introduction to the Node Schema Language part D ooococonininnncnncnnnnonncnnncnnonnoncnnonononononacnccncnnnos 12 4 1 Principles node schemas and nodes instances sesssseeeeeeeeeseeeeeeeeeseeseeeseeesesaeeaseeeeees 12 4 2 Specifying the contents Of a NOE eee eseeseeeeeeeseeseeeeeceseeseeaeeecseeseeaeeaseessesseeaeeaseeeeees 12 4 2 1 Content elementsiat canoas ein treed ieee eee 12 4 2 2 Tuple and non tuple element eeeeseseeeeeeeseeseeeeeeeseeseeeceesesseeaeeessesnesaeeeseeseres 13 4 2 3 Selection CONGILIONS inercia a ainda 14 4 3 LAKS eoi OO 14 4 3 1 Navigation Inks viii id in 14 4 3 2 Expand n place links iii ai 15 4 3 3 Inclusion Links 2 0 eeeeesessees
15. SQLonDB String sql String db boolean select executes the sql statement on the LAZYDICT connection the connection to the Lazy dictionary database public static QueryResult execSQL String sql boolean select Query results are stored in a QueryResult object defined as follows e class QueryResult Statement stmt public ResultSet result public boolean valid true false error in query processing public String msg error message if valid false public String sql public int nbUpdated 0 Examples static String updel String keyval String val QueryResult ql execSQLonDB delete from T1 where TK keyval Z CONNECTION false QueryResult q2 execSQLonDB update T2 set A val where T2K keyval Z CONNECTION false String r if ql valid r ql msg if q2 valid r q2 msg return r The DBServices and QueryResult classes are located in webapps lazy WEB INF classes To compile methods that refers to them it is necessary to add their location to the CLASSPATH For instance javac MW java classpath STOMCAT_HOME webapps lazy WEB INF classes d TOMCAT_HOME webapps lazy WEB INF classes 9 3 How the instantiation process works 9 3 1 translation to SQL 9 3 2 order in which things are executed 10 Language reference semantics Evaluation principle startrule define project project identifier nodetype xml
16. current session These variables are USER the current username GRP the datagroup the user is working in LANG the user s preferred language They can appera anywhere in the definition of a node in the content or in the selection part Example 6 12 2 Input variables An input variable is a variable whose value is either entered by the user in an input field set var textarea textfield etc or obtained as the value of an expression set var expr Variables can only be set in the definition of an active link It is important to note that the value of an input variable is not available until the active link has been followed by clicking the link s button Hence it cannot be used elsewhere in the node that sets its value more precisely reference to the variable in the node will yield to old value of the variable However input variable values can be passed as parameter to the target node of the active link with the variable syntax Since no data base action is to be taken the link s button simply has a do navigate action Within the target node and subsequently visited nodes expressions of the form variable will yield the value of the corresponding input variable Example node Selector input a word and a level of detail then go to the search node active href Works with_name word lt p gt Word of the work s title set word textfield 20 lt p gt Level of detail 1 9 set detail textfield
17. e the command window Step3 Start the node server with the provided tomcat servlet container Open a new shell terminal command window and make sure the environment variables are cor rectly set Then type Unix Linux MacOSX startns sh Windows NT 2000 XP C gt cd SLAZY HOMESNbin C lazyenv C startns do not close the command window This starts the tomcat servlet container which is a HTTP server that manages servlets The node server is a servlet named lazy ns Step 4 Start browsing the virtual museum With your preferred Web browser open the example home page at http 127 0 0 1 8080 lazy and follow the links to the generated nodes if your Windows machine is not connected to a network it may take some time before it realizes that it can connect to itself sometimes more than 1 min you can also try to stop and restart loading You can also choose to explore the Lazy system by following the Lazy Administration link In this case you ll need to log in as a Lazy administrator user admin password x If you already use ports 8080 and 8007 for another purpose you can select other ports in the tom cat configuration file STOMCAT_HOME conf server xml Step 5 Stop the node server Open a new shell terminal command window and make sure the environment variables are cor rectly set Then type Unix Linux MacOSX stopns sh Windows NT 2000 XP C gt cd SLAZY HOMESNbin C lazyenv C stopns 3 Using the N
18. e the museum no by a more explicit one This node is used by mw_Work node mw_Owned w href mw_Museum museum name from ownership museum selected by work w and museum mno 4 5 Some design guidelines Designing node schemas that form a good hyperspace is like designing software or buildings there is no general method However you can find design ideas and a design and analysis meth odology in the papers published by the ISI research group http cui unige ch isi reports What follows is a brief presentation of design guidelines that can help you creating a first version of a hypertext view on a database Although a database schema obeys to different design objectives and requirements it can serve as a starting point for a hypertext view design The idea is to create node schemas that correspond to the database tables and links that correspond to the foreign keys between these tables It can be summarized in the following points Nodes to display database tuples For each table T create a node t to display the tuple that corresponds to a key value passed as pa rameter The general node pattern is node t p attributes of T from T selecty by Tkey p where TKey is a key of T Of course if the key of T is made of several attributes K1 Kn t must have n parameters pl pn and the selection condition must be K1 p1 and and Kn pn Create hypertext links according to the foreign keys For each foreign k
19. ed from Oracle s site they are called ora cle jdbc driver OracleDriver and come in zip files e g classes12 zip Hsqldb the hsqldb driver is called org hsqldb jdbcDriver it comes with the Lazy distribution in file lazycat webapps LAZY database hsqldb lib hsqldb jar One important point is to find the correct URL schema to access your database through JDBC Here are some examples Oracle thin client jdbc oracle thin Ohostname 1521 instancename ODBC source jdbc odbc sourcename hsqldb jdbc hsqldb hsql hostname 2 Define a new database connection and a new project a Go to http 127 0 0 1 8080 1azy ns a ADMIN all and click the Connections link b Create a new database connection c Define a new project and associate it to the new database connection all the nodes of a project access the same database given by the project s database connection d Start creating node schemas in the new project That s all 5 2 Installing the Lazy dictionary in an existing database 1 Install the appropriate JDBC driver see above 2 Update Lazy properties and LazyCompiler properties Edit the files Lazy properties and LazyCompiler properties in TOM CAT HOME webapps lazy WEB INF classes and modify the following lines database url your database JDBC URL database user your database user name sa for hsqldb database password your dataase password empty for hsqldb database driver class name of your JDBC driver Although these
20. eeceseeseeseeecseeseeseeascesecseeaesesseesesaeeeseessesseeaeeessesaeeaseaseeeres 16 Aa Examples ts ie topes ove eth lees Pica eves escess ie viaedves geascval otaadea evesceul SRi ee aaeain ae ed 16 4 5 Some design guidelines sirrien aens eden ss asse 17 Creating Hypertext Views on Existing DatabaseS cococonicnnonnonconcncnocnonnonncnncnononnonnonnnonncnnonnnn 20 5 1 Keeping the Lazy dictionary in the HSQL database ooononincnncnncncnnnccnonnnnnnncnncnnononacnccnncnnon 20 5 2 Installing the Lazy dictionary in an existing database ooconccncnncncnnoccnoonncnncnnncononnnannnonacnnos 20 The language part ID sissies civisesacied ei ek asi eis nek eben oil eka eya ons aa per alos vi ea eye E aE peyi aeae 23 6 1 More details on the evaluation of tuple and non tuple Cl MERtS u vuererrereeoosesooones 23 6 2 Conditions and embedded QUETICS 0e002Litverteoterererorosaonoonoonossonaonoonosaossonoooonossoooonooonon 23 6 3 More details on LINKS 20 ce eeeeeseeseecceeeeeseeescesecseeascesessesseeecseeseeseeaeeessesseeaeeessesseesseaseeeeees 24 6 3 1 Generated URES uma aaa 24 RON 24 6 4 Active Links curia oe 24 6 4 1 Principle anto aeads 24 6 4 2 Syntax and semantics ee eeeeeeeseeseeseeeeeeeeeseeeceeesecseeaeeessesseeaeeesseeseeaeeeseesesaeeaseeseeees 25 6 4 3 A Remark about access rights cceeseesesseeseeeeeeeeeseeecseeseeseeaeeessesseeaseesseeneeaseaseeeeees 26 6 5 Inputting Values with Active Links ccecessssces
21. ement of the form include _MW artistAbbreviatedName a will call the static method artistAbbreviatedName of class MW and include the resulting string in the node content A node method must have one of the following signatures static String methodname String parameterl String parameterN static String methodname String parameter class MW static String artistAbbreviatedName String n String af n int x n indexOf if x gt 1 af n charAt 0 n substring x 1 return af other methods The second form is intended to implement nodes with a varying number of parameters For instance static String concatIf String params String r for int i 0 i lt params length 1 i 2 if params i equals yes r r params i 1 return r This class must be compiled and the class file stored in the webapps lazy WEB INF classes di rectory Use for instance the following compilation parameters javac MW java d TOMCAT_HOME webapps lazy WEB INF classes Accesing the database from an external method The following Lazy server methods can be invoked from an external method to execute SQL statements on a database corresponding to a database connection class DBServices sql the statement db name of the database connection select must be true for a SELECT statement and false for an INSERT DELETE UPDATE public static QueryResult exec
22. ess rights 6 5 Inputting Values with Active Links 6 5 1 Input Elements Active links are also the standard way to input values to the database For this we use attribute setting elements with input expressions An input element takes the form set attribute name expression textfield width textfield width initial value textarea nb lines width textarea nb line width initial value select expression_list include node_ref free input element Attribute name must refer to an attribute of the table mentioned in the action element A node to create a new artist node mw_new Artist lt h2 gt Adding a new artist active href mw Artist index lt p gt Unique identifier set ano textfield 10 a number lt p gt Name set name textfield 60 lt p gt Birthdate set birthdate textfield 10 lt p gt Deathdate set deathdate textfield 10 on Add do insert artist Although this node will act on the artist table by inserting a new tuple its content does not de pend on any particular table When generated this node displays the heading text four input fields for ano name birthdate and deathdate and an Add button When the user clicks on on Add the system takes the input values to form a new tuple inserts this tuple into the artist table and then jumps to the node mw_Artist_index It is not mandatory to define all the table s attributes to insert a ne
23. etwork or database problem 7 3 Users A Lazy user is characterized by his or her username and password Access rights to Lazy nodes and database tables can be assigned to users When a new session is established the user is auto matically logged in with ther username PUBLIC If he or she requests a node that has access re striction he or she will be asked to enter a username an password In node schema the session variable USER returns the username Note In the current version session variables are implemented by a string substitution mecha nism If the substring variable appears in a string it is replaced by the variable s value As a consequence the string should never appear in this form in a string 7 4 Datagroups Datagroups are intended to horizontally partition data between different groups of users For instance the same database could be used to manage data belonging to different departments Datagroups are useful when different groups share the same data structures but not the same data The global variable GRP represents the datagroup of the current session MORE DETAILS HOW AND WHY DESIGNING DB SCHEMAS WITH GROUPS The dictionary schema given in appendix shows the relationships between all the security and project management related concepts It is a UML view of the Lazy dictionary tables 8 Encryption 8 1 Security in Lazy Because the property files Lazy properties and Compiler properties co
24. ey UK of table U in T i e UK holds a key value of U it points to a tuple of U add a navigation link to u in t node t p attributes of T href u UK some anchor text other links from T selected by Tkey p Add inverse links To allow navigation in the reverse direction from u to t it is necessary to create an additional node to display all the tuples of t that point to a given tuple of u identified by its key value node _t from u uKey href t K K from T selected by F uKey This node must be accessible from u through an href link node u k fou href t from u UKey from U selected by Ukey k Create entry points Entry points are starting points for the navigation within your hypertext view The simplest entry points are index nodes that display anchors to all or a subset of the tuples of a table They are de fined as follows node t_idx href t Tkey some attribute s from T Inclusion to factor out common parts The inclusion mechanism is interesting to re use nodes and thus to avoid writing many times the same statements For instance the following node defines a node footer also called navigation bar that can be included in many nodes node mw_To_index lt hr gt href mw Work index Work index href mw Artist index Artist index href mw _ Exhibition index Exhibition index Evolve to a more efficient hypertext design The
25. files are not accessible form the Web they should be carefully protected on your file system since they contain database passwords 3 Modify the scripts to indicate the location of the JDBC drivers The JDBC_DRIVER environment variable indicates where the JDBC drivers are Update its defi nition in SLAZY HOME bin lazyenv xxx by adding the location of the the new driver s 4 Create the Lazy dictionary Create the tables that will handle the Lazy dictionary node definitions users roles grants etc The LAZY HOME admin directory contains the SQL scripts to create these tables lzydict schema sql the tables that stores node definitions lzydict hsql schema sql the same for Hsqldb lzydict ora schema sql the same for Oracle admin schema sql table schemas for all the security administration related tables admin hsgql schema sql the same for Hsqldb admin init sql initial values for the administration tables NOTE Although SQL is supposed to be the standard data definittion query and manipulation language every DBMS has its own interpretation of that standard Moreover many important functions are left undefined in the standard data conversion string manipulation etc Hence the specific definition scripts and node definitions 5 Recompile the Lazy administration and development nodes Compile the node schemas that are in LAZY_HOME admin These nodes define the administra tion and development environment to create and compile
26. ge Node instances are dy namically generated by a node server that takes as input a compiled formed of the node schemas A node schema specifies the table s from which the node s content is to be drawn the se lection and ordering criteria the elements that form the node content and links to other nodes The node definition language is described in sections 4 6 and 9 of this manual The node sche mas must be compiled in order to be usable by the node server The compilation process first checks the schema s syntax then translates it into a form in fact SQL queries that is directly ex ecutable by the node server It is described in section 3 2 Installation 2 1 Requirements Since Lazy is entirely written in Java you need a Java 1 4 run time environment installed on your machine you can get it from Java soft http java sun com Lazy does not work with Java 1 3 or earlier versions because it uses the new Java encryption scheme The Lazy node server is a servlet application So you need a servlet container server You can either use the tomcat servlet container that comes with the Lazy distribution or download a more recent version from http jakarta apache org 2 2 Downloading and installing Download the zip file from http cui unige ch isi lazy4 download 1 Unzip or gunzip the file into some directory This should create a new directory named lazy x y x y is the version number that contains the following subdirectories
27. he list of node schemas of the MW project ON Node NODE project MW 4 E ed http localhost 8080 lazy ns a NODE pr Qe Admin III Projects Users Data Groups Roles DB Connections Project MW O new Node II Dump sources 2041 WorksBetween Instantiate 20 mw_Artist Instantiate 2983 mw_Artist_index Instantiate 20 mw_Artist_name Instantiate 204 mw_Contemporary Instantiate 20 mw_Content_of_exh Instantiate Click the New Node link to create a new node this opens a node input page In the text field type the following node schema text node myNode lt h2 gt My Artist Index lt p gt name birthdate deathdate from artist nan Node NODE new_node MW 4 a e http localhost 8080 lazy ns a N G Q7 Google Admin III Projects Users Data Groups Roles DB Connections A Project MW Compile y node myNode lt h2 gt My Artist Index 1 p name birthdate deathdate from artist a v 3 j Ouvrir http localhost 3080 lazy ns a ADMIN all Click the Compile button to save and compile the node and return to the list of node sche mas Now there is a myNode line in the node list with either a red or green ball The red ball indi cates a compilation error In this case click the pencil icon to edit the node Once the ball is green click the Insta
28. height x width lt p gt href mw Artist after 1500 View artists born after 1500 from work selected by author artist order by c date It displays the title creation date support height and width of all the works created by the artist whose number is given as parameter After the work list it contains a link to the list of artists born after 1500 OOO Node MYSITE m 4 a e http localhost 8080 la Artists born after 1860 Alberto Giacometti born 1901 works Charles Sheeler born 1883 works Jackson Pollock born 1912 works i Kasimir Malevich born 1878 works AAA Node MYSITE mw_Works_by_artist 1 Kurt Schwitters born 1887 works d A n 3 Fa A Nicolas de Sta l born 1914 works 2 lt CG Bhttp localhost 8080 lazy ns a MYSNG Pablo Picasso born 1881 works Pierre Bonnard born 1867 works Piet Mondrian born 1872 works Robert Delaunay born 1885 works Nu dans la baignoire 1925 Oil on canvas x The Breakfast Room c 1930 31 Oil on canvas 62 7 8 inches x 44 7 8 inches View artists born after 1500 4 3 2 Expand in place links In addition to standard hyperlinks as found in HTML it is possible to define expand in place links These links have a different behaviour when the anchor is clicked it is replaced within the current page by the referred node Replace the href keyword by expand href in the mw_Artist_after node schema recom pile it an
29. iler translates Lazy expressions into SQL statements that are directly executable by the node server Thus to instantiate a node scheme of the form node n p x Lys Z from T selected by C the following SQL statements will be executed against the database 1 PRE first row of select x from T where C 2 ITEMS select y from T where C 3 POST first row of select z from T where C x y and z are the direct translation of x y and z into SQL The translation principle is as follows attribute name gt attribute name string gt string with doubled function name gt function name parameter name gt special placeholder that will be replaced by the actual parameter value before executing the SQL statement operators and parenthesis gt same operators and parenthesis If the from table part is absent from the node schema the select statement is executed on a special table called DUAL that contains only one tuple Thus even for non database or con stant nodes the SQL engine is called The current version of the compiler does not check if the attribute and function name really exist in the database So wrong names will cause instantiation errors that will be reported when instantiating the node Note that normally the PRE and POST statements should yield only one row because they are intended to display aggregate values SUM AVG COUNT etc Since the semantics of SQL operators and functions may vary from
30. lowing node schema is to display a list of artists born after a given date d node mw Artist after d lt h2 gt Artists born after d lt ul gt lt li gt name born birthdate from artist selected by birthdate gt d order by name An instance of this node will contain a title the lt h2 gt element followed by an unnumbered list lt ul gt of artists A typical instance of this schema with d 1880 looks like Nan Node MW mw_Artist_after 1880 4 ial ed http localhost 8080 lazy ns a M Artists born after 1880 Alberto Giacometti born 1901 Charles Sheeler born 1883 Jackson Pollock born 1912 Kurt Schwitters born 1887 Nicolas de Sta l born 1914 Pablo Picasso born 1881 Robert Delaunay born 1885 The non tuple elements may also contain the usual aggregate functions sum avg count min and max applied to table attributes Note that if the selection expression does not yield any tuple the node will be totally empty Even the non tuple elements are not generated This property is sometimes useful when one wants to display something only if a given condition is satisfied 4 2 3 Selection conditions The selection condition is a boolean expression made of literal constants character strings or numbers attribute names parameter names arithmetic and logical operators comparison op erators or function calls The logical operators are and or and not The comparis
31. ly defines a session variable that bears the same name as the attribute no input_field textfield simple_expr simplexpr textarea simple_expr simple_expr simplexpr free field y select include link simple expr simple expr A free input field indicates that the given field completely specifies the input method with html or xml tags The input method must provide a value for a parameter named av on_action on string_expression do navigate insert table_identifier delete update table_identifier keyvalue keyvalue Generate a clickable button with the given label and defines the associated database action Pos sible actions are navigate no database action simply navigate to the referred node This is used to let the user enter variable values or parameter values insert t inserts a new tuple in table t the attribute values are given by the set attr fields that appear in the active link anchor delete t al vl deletes all the tuples x from table t such that x al v1 If vi is not specified the value of the ai attribute of the current tuple is taken Thus to delete the tuple corresponding to the displayed content it is sufficient to specify delete T K1 K2 where K1 K2 form a key of T and T is the base table of this node update t al vl updates all the specified tuples from
32. ments expression condition 11 Glossary of terms Node schema A text written in the Lazy language that defines how to construct a node instance usually an HTML or XML page It is comprised of a selection part a content part with links and parameters Node instance A hypertext node usually a HTML or XML page that is part of a hypertext view It is an in stance of a node schema Its content depends on the schema definition the actual parameter val ues and the current database contents tables A node is instantiated each time the user clicks on a link to the node or when the node is include in another one see inclusion link Node type The type of content produced when instantiating a node Currently defined types are html xml pure html no heading tag is generated pure xml svg The node type is specified at project level 1 e all the nodes of a project have the same type Node server The role of the node server is to answer to node requests by instantiating the required node schema with the given parameters It also performs database actions corresponding to active links Node compiler The program that checks the syntax of a node and transforms is different parts into SQL state ments which may still contain placeholders for parameters Link A way to interconnect nodes The source of a link is a content element of a node its destination is a node Lazy links can have four different behaviours refe
33. mpile and install your node schema by typing Unix or Windows lc myNode lzy Once you get an error free compilation instantiate a node by sending the following URL to the node server http 127 0 0 1 8080 lazy ns a myNode It should display a list of artists together with their birthdate and deathdate The LAZY system is a dynamic system once a node definition has been modified and re compiled the new version is immediately available to the clients there is no site generation phase Try modifying myNode recompiling it and reloading the corresponding page into your browser IMPORTANT NOTE To speed up complex node generation the Lazy node server maintains a server side node cache When a node schema is recompiled all its instances must be erased from the cache However in the current version the batch compiler does not clear the cache This must be done manually from the Lazy administration page by clicking the Clear node cache link 4 Introduction to the Node Schema Language part l This section presents the basic elements of the Lazy node schema language The examples are based on a simple database that stores information about a digital museum The database schema is as follows key attributes are in bold Work wno author title c_date height width picture Artist ano name birthdate deathdate Exhibition exno title desc organizer Museum mno name location URL Ownership work owner acquisition Art_cn
34. ng With inclusions ccccecescceseeseeseesecsececeeseesecsececeesecsecseceeeesecsecseeeeeeaeeseeeeeeneeas 35 9 2 Java Nodes iia lala alias 35 9 3 How the instantiation process works ecescesceesceseeseesececeeceeseesecsececeeseesecseeeeeeaeeseeeeeeneens 36 9 3 1 translation to tS OL kreve vese ee edie seas aa 36 9 3 2 order in which things are executed ecesseesseeseesecesceceeseesececeeeeaecseceeceaeeaeeeeneeeaes 36 10 Language reference semantics ceeeceesceeeceseeseesecseeeeeseesecsecseesecaecseceseesesseceeeaeeaeceeeeeeaees 37 11 GIOSSALY OF CELTS A A A dd 41 12 BIO keep aka vite ie ia ke vese va sod E kek eks aie EEE E EEA EAR E iioi 44 1 Introduction Lazy is a language and system to publish databases on the Web and to create Web application interfaces In fact Lazy creates hypertext views of a database A hypertext view is a set of nodes the Web pages and hyperlinks that represent the contents of the database In the declarative ap proach the hypertext components nodes and links are derived from the database content rela tion tuples according to a hypertext view specification as shown below Database Hypertext View relations Generation Hypertext View Specification Node schemas Hypertext View Nodes Web Pages A hypertext view specification consists of a set of node schemas Every node Web page is an instance of a node schema written in the Lazy specification langua
35. ntain the database password of the db where the Lazy dictionary if not the data is stored it is of the highest importance to protect them against unauthorized access Normally read access to these files should be granted only to the Lazy owner 8 2 Why encrypt Lazy can connect to several databases the connection password of these databases should be protected In addition the user passwords are stored in the dictlazy database These password should also be protected Finally an probably most importantly when Lazy is used to update a database important information such as table names attribute names key attribute values etc may appear as hidden fields in the pages sent to the user A malicious user 1 get information about the database schema of the application and 2 forge pages containing updates in forms and send them to the server in order to slip wrong data into the database 8 3 What is encrypted When encryption is turned on the following items are encrypted e All user passwords e All database connection password except the initial lazydict connection e All the table names attribute names key attribute values appearing in forms in HTML pages send to the user 8 4 How to migrate to the encrypted form The first step consists in choosing a permanent encryption key this key will encrypt user pass words and database connection passwords it must never change This key made of 16 hexa decimal digits is
36. ntiate link OOO Node NODE instantiate MW myNode l A 4 gt Mhbttp localhost 8080 lazy ns a Ni Qr Google myNode Open and the the Open button to generate a Web page from this new schema OOO Node MW myNode lt Ha Ha OBhtrp localhost 8080 lazy nsza MG 5 Qr My Artist Index Pierre Bonnard 1867 1947 Vincent van Gogh 1853 1890 Georges Pierre Seurat 1859 1891 Claude Monet 1840 1926 Robert Delaunay 1885 1941 Kurt Schwitters 1887 1948 Piet Mondrian 1872 1944 Charles Sheeler 1883 1965 Pablo Picasso 1881 1973 Kasimir Malevich 1878 1935 3 2 In batch mode Create a new text file say myNode 1zy with the following content define project MW node myNode lt h2 gt My Artist Index lt p gt name birthdate deathdate from artist end A source file must begin with define and end with end it may contain one or more node schemas The project MW statement indicates that this node belongs to the MW project Open a new terminal command window and make sure the environment variables are cor rectly set and that the lazyenv script has been executed as indicated in the installation instruc tions under Start the node server In necessary start the database server and the node server the node compiler stores the compilation result an executable form of the node schema into the database Co
37. ode Compiler The node compiler checks the syntax of a node schema and translates it into a form that is directly executable by the node server It can be used either from the Lazy interactive development envi ronment or in batch mode from a terminal command window The following paragraphs show how to define and compile a new node for the virtual mu seum example both interactively and in batch 3 1 With the interactive development environment The interactive development environment can be reached from the Lazy start page http 127 0 0 01 8080 lazy by following the Lazy Administration link The Lazy ad ministration page has links to projects users database connections etc Navigate to the Projects page to see all the currently defined projects At this point the Lazy server may ask for a username and password by default user ADMIN has password x ONO Node ADMIN all_projects 4 ed ski A http localhost 8080 lazy ns a ADMIN a Q7 Admin Ill Projects Users Data Groups Roles DB Connections a Projects 23 Y ADMIN Nodes Users data and project management Access rights AIS ICON Nodes A set of userful icons Access rights 2I Y MW Nodes A mini virtual museum Access rights 23 Y MYSITE Nodes A demo project Access rights 2 Y NODE Nodes Node management development Access rights To define a new node in the virtual museum follow the Nodes link of the MW project It leads to t
38. on operators are lt lt gt gt lt gt like is null is not null The arithmetic operators are The main difference with SQL syntax is that strings are delimited by double quotes instead of single quotes Embedded queries are not allowed in conditions However existential conditions can be ex pressed with a specific syntax as we will see in section 6 4 3 Links The Lazy language provides three kinds of links the usual reference hypertext links inclusion links to build complex contents by including nodes in one another and expand in place links that are inclusion links triggered by a user action 4 3 1 Navigation links Any content element or list of elements can serve as the source anchor of a reference link An expression of the form href target node name parameter value anchor element s defines a reference link to a target node whose source anchor the clickable text is the anchor element s Exemple Here we have added to the mw_Artist_after schema a link to a node that shows the works of art of each artist in our node mw_Artist_after d lt h2 gt Artists born after d lt ul gt lt li gt name born birthdate href mw_Works by artist ano works from artist selected by birthdate gt d order by name The mw Works by artist node can be defined as node mw_Works by artist artist lt p gt lt b gt title c date support
39. onds to the SQL expression not exists select from table where condition and not condition The multi table form is forall table var table var condition gt condition which is true if all the tuples var var in table x x table that satisfy condition also sat isfy condition 6 3 More details on links 6 3 1 Generated URLs Normally URLs are automatically generated by the Lazy system when you write an href state ment However if you want to refer to a Lazy node from a standard HTML page or directly by entering a URL in the address field of the browser you must use the following URL scheme http hostname port lazy ns a node namesu parameter su parameter 8u the standard port used by the tomcat server is 8080 For example to open the node mw Artist after 1880 on the local machine you must open http 127 0 0 1 8080 lazy ns a mw Artist after 28au 1880 6 3 2 6 4 Active Links 6 4 1 Principle An active node is a node that contains active links An active link is a reference link href that triggers a database action when traversed In addition to usual elements the source anchor of an active link must have one or more attribute setting elements and exactly one action element The general syntax of an active link is active href node name parameters standard or attribute setting or action elements An attribute setting element has the form set attribut_name expression and an ac
40. rence jump inclusion expand in place and active Reference link A link from a content element to a node When the node is instantiated such a link appears as an undelined text an HTML anchor When it is clicked the referred node is instantiated an replaces the current node the user jumps to the referred node Expand in place link A link from a content element to a node When the node is instantiated such a link appears as an undelined text an HTML anchor When it is clicked the content of the referred node is instanti ated in place it replaces the anchor text Inclusion link A link intended to include the content of the target node withing the source node at the link loca tion Inclusion links are useful to create complex node contents Active link A link that triggers a dabase action when it is followed Project A set of nodes that make up a hyperspace intended for a specific purpose All the nodes of a pro ject have the same type html xml purexml purehtml and refer to the same database connec tion Every node belongs to exactly one project Thus the full name of a node has the form pro jectname nodename Database connection an access to a particular database schema It is comprised of a database URL e g jdbc hsqldb hsql localhost a JDBC driver class e g org hsqldb jdbcDriver a username and a password The URL and driver are dbms specific refer to your dbms documentation User
41. rts a new tuple into artist and then jump to the node mw_Artist ano The ano notation indicates that the value given to the ano attribute in the set ano textfield 10 element must serve as parameter to instantiate mw_Artist In this case it will jump to the node that displays the artist with the number we just entered 6 6 Active Nodes Active nodes offer yet another means to update the database when navigating a hypertext view An active node is a normal node that is equipped with a list of pre actions These are database actions that are executed just before the instantiation of a node The syntax for pre actions is node N parameters from selected by order by on open action Actions can be either insertions deletions or updates expressed with the following syntax Insertion insert tablename attribute value attribute value it corresponds to the SQL statement insert into tablenamelattribute attribute values value Value Deletion delete tablename condition which corresponds to the SQL statement delete from tablename where condition Update update tablename conditions set attributel valuel attributen valuen which corresponds to the SQL statement update tablename set attributel valuel attributen valuen where condition Pre actions are particularly useful when updating the database requires several actions on differ ent tables
42. run a lazyenv script that sets additional variables that depend on these ones Unix Linux MacOSX Add the following lines to your login or bash_profile with bourne shell or bash export LAZY HOME your lazy home directory export TOMCAT HOME SLAZY HOME tomcat or your own tomcat home export JAVA_HOME your java installation directory source SLAZY HOME bin lazyenv sh Unix Linux MacOSX Place the following lines in your login or bash_profile with cshell export LAZY HOME your lazy home directory export TOMCAT HOME SLAZY HOME tomcat or your own tomcat home export JAVA HOME your java installation directory source SLAZY HOME bin lazyenv sh Windows NT 2000 XP Place the following lines in your autoexec bat or define these variables in the System gt Advanced gt Variables settings set LAZY HOME your lazy home directory for instance C lazy 4 3 set TOMCAT HOME SLAZY HOME tomcat or your own tomcat home set JAVA HOME your java installation directory for instance C jsdk1 4 1 run SLAZY HOMESbin lazyenv bat Caution Avoid white spaces and other special characters in these variables they will probably cause errors when starting the tomcat server Step 2 Start the database server Open a new shell terminal command window and make sure the environment variables are cor rectly set Then type Unix Linux MacOSX runServer sh Windows NT 2000 XP C gt cd SLAZY HOMESNbin C lazyenv C runServer do not clos
43. seceeseeseceeceseeseeseceeceneeseeseceeceseeaesseeeeeeneeas 26 6 5 1 Input Element 00 ie eeeesesseeeseeseesceecseeseeseeeceesessessceesseesesseeaseessesseeaseeseeesesaeeaseeeeees 26 6 5 2 Using the Input Values as Parameters ccecceccescesececceceeseeseceeceeeeseeseceeeeaeeaeeereeeeeaes 27 6 6 Active Nodes vi piti vevi peti ayi pasi weka kle die bie ined ni akne yo ea tada di 27 6 7 Session Variables it aaa 28 6 8 Some design principles imac 28 6 8 1 Collecting Input values iuenitaiinda dape odie 29 A NON 29 6 9 Active Nodes and LINKS ro nenio neea a a a a a aa a 29 6 10 Designing active NODES orna as 30 6 11 PReZACHUONS wal ken done Al daa KODE eh AA 30 6 12 Global variables minninganna a it 30 6 12 System vantables estricto caes etica 30 6 12 22 Input variables AA A a e S 30 6 13 Tnternationialized stt1i ia aa daa 31 L E A AN 32 7 1 PO AAA a 32 7 2 COMMS CHL ONS 228 seats ri e eo eo lente endo ai at e aou ob TS 32 7 3 IEA NA E NEATE ANNE SAA A RE W MAP e AA Y NANA ARE TEA SE MAN AA BAN KA 32 7 4 Datagroupst dial id ld li 32 8u EN PO is 33 8 1 MSCULILY MA A totes id IA 33 8 2 WAY ENGEY PEEP a A a 33 8 3 What 1SENCIVpted Kite stad st pot abi acota span sida ok Melee ease NE e ld EL sud A L ai 33 8 4 How to migrate to the encrypted form 0 ec eececescesessecesceseeseeseceeeeeeesecseceeeeeeseeseeeeeaeeas 33 Oy cLeansuase patata ao ankwa bo aaa a we be ou paka kb l ed ea a kok bwd e ena A 35 9 1 Computi
44. that this user has this role in all datagroups Servlet Servlet container this is an http server that can host servlets written in Java Apache Tomcat is the reference servlet container When the server receives a URL request that correspond to a servlet it invokes the doGet or doPost method of this servlet 12 Bibliography See http cui unige ch isi reports Appendix A The Lazy dictionary al lazy naturals va projectid name O nodename projectid operation nbparams pre E items connectld post driver collection url dbconnection selector useerdb etc ordering groupby plaintxt status error cachesiez pwddb PE lazy balang projectlid projectlid textid lang lib textid en m lazy roles userid lazy_roles pue oea ES admin defaultgrpid userld grpld roleld catld codel ov m Oooo listDef
45. tion element takes one of the following forms on button label do insert table name on button label do delete table name key attributes on button label do update table name key attributes So for instance the following node has an active link that when clicked creates a new tuple in table T and jumps to node m node aNewT pl p2 If you click the following link it will insert pl ki p2 into T active href m set A pl set B p2 on Insertion do insert T 6 4 2 Syntax and semantics The link actions perform the basic SQL operations insert delete and update set Al el set An en on b do insert T insert into T A1 An values el en on b do delete TIK1 el Kn en delete from T where K1 el and and Kn en There exist an abbreviated form on b do delete T K1 Kn is an abbreviation for on b do delete T K1 K1 Kn Kn when the expressions are simply the attribute values of the displayed tuple For instance node deleteAnyWork lt p gt title active href deleteAnyWork on delete do delete Work wno from Work picture set Al el set An en on b do update T K1 el Kn en update T set Al el An en where Kl el Kn en the abbreviated form on b do update TIKI Kn means on b do update TIKI KI Kn Kn Examples of active links are given in the next subsection 6 4 3 A Remark about acc
46. try clicking on links in the instance mw Artist after 1860 ANOO Node MYSITE mw_Works_by lt W http localhost 8080 lazy ns eip Artists born after 1860 e Alberto Giacometti born 1901 works e Charles Sheeler born 1883 works e Jackson Pollock born 1912 works e e Kasimir Malevich born 1878 Bi Supr matisme no 50 1916 Oil on canvas x Suprematist Composition White on white 1918 1915 dated View artists born after 1500 Kurt Schwitters born 1887 works Nicolas de Sta l born 1914 works Pablo Picasso born 1881 works Pierre Bonnard born 1867 works Piet Mondrian born 1872 works Robert Delaunay born 1885 works 4 3 3 Inclusion links The third kind of links is inclusion links An inclusion link immediately includes the content of the referred link at the indicated place An inclusion link does not have any anchor text Replace href mw_Works by artist ano name by include mw_Works by artist ano in the node schema and recompile it The node mw_Artist_after 1880 should now look like this Inclusion and expand in place links are powerful mechanisms to build nodes with rich heteroge neous and adaptive contents Indeed inclusion and expand in place form the basic construct to jump out of the relational box i e to build data presentation that don t look like tables or list of record In fact with inclusions it is possible in most cases to avoid join
47. ty artist country activity Ex_content work exhibition comment 4 1 Principles node schemas and nodes instances The definition of a basic node schema takes the following form node node name parameter name content specification from tables selected by condition An instance of this schema an actual hypertext node is obtained as follows 1 select the tuples of the specified table s that satisfy the given condition 2 for each selected tuple generate a content according to the content specification For example a node generated from the schema node WorksBetween d1 d2 title height width from work selected by dl lt c date and c date lt d2 will contain the title height and width of all the works of art created between the dates d and d2 given as parameters The actual content of a node instance depends of course on the parameter values and on the current database contents 4 2 Specifying the contents of a node 4 2 1 Content elements The content of a node is specified by a list of elements An element is either a database attribute or a quoted string or a number literal or a parameter name or an artithmetic expression An ele ment or a sequence of elements usually has a markup type and attributes an HTML or XML tag defined with the following syntax tag attribute expression element This notation is an abbreviation of the standard HTML XML notation lt tag attribute
48. value gt element lt tag gt We can now refine our previous example by adding HTML tags and white spaces or texts to produce a niceer HTML document node WorksBetween d1 d2 lt p gt lt b gt title c date height x width from work selected by dl lt c date and c date lt d2 You can try compiling and instantiating this node as indicated in section 3 The following screenshot shows the instance WorksBetween 1880 1920 on the example database OOO Node MW WorksBetween 1880 1920 Gia la e http localhost 8080 lazy ns a MW WorkG Qr Go The Starry Night 1889 29 inches x 36 1 4 inches Port en Bessin Entrance to the Harbor 1888 21 5 8 inches x 25 5 8 inches The Windows 1912 51 1 4 inches x 6 feet 5 inches Picture with Light Center 1919 33 1 4 inches x 25 7 8 inches Suprematist Composition White on white 1918 19 inches x 31 inches Pier and Ocean 1915 2 ft 10 1 2 in x 3 ft 9 1 4 in La Montagne Sainte Victoire 1903 1904 x Supr matisme no 50 1916 x 4 2 2 Tuple and non tuple elements While the content elements placed between and are generated for each selected tuple the ele ments outside or enclosing the are generated only once They generally serve as titles header or footers that appear only once in a node In addition these elements may contain aggre gate functions like sum max min count Example The purpose of the fol
49. w tuple only those that are either part of the primary key or not nullable are required The following node enables the user to change the name of a given artist node mw_upd name Artist w lt h2 gt Changing the name of artist no w active href mw_Artist w lt p gt Name set name textfield 60 name on Update do update artist ano href mw_Artist w Don t change from artist selected by ano w This one adds 5 to the birth date of an artist very useful indeed node mw_add5 Artist w lt p gt Click on the Plus 5 button to add 5 years to the birth date of name active href mw_Artist w set birthdate birthdate 5 on Plus 5 do update artist ano from artist selected by ano w 6 5 2 Using the Input Values as Parameters The input values can be used as parameters to the destination node For instance the fol lowing node reads attribute values for a new artist creates a tuple when the button is clicked and then jump to a node that displays the newly created artist node mw new Artist 2 lt h2 gt Adding a new artist active href mw Artist ano lt p gt Unique identifier set ano textfield 10 a mu ber lt p gt Name set name textfield 60 lt p gt Birthdate set birthdate textfield 10 lt p gt Deathdate set deathdate textfield 10 on Add do insert artist When the Add button is clicked it inse
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