SciSPARQL User`s Manual
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1. Note that in this case we are required to include friend in the result list as the bindings for this variable are expected to be unique URIs or dataset unique blank nodes identifying different persons If we apply the DISTINCT only to the f riend_name variable we will get a set of unique names which might be shorter as different people might happen to be namesakes There may be more than two UNION branches in the same conjunct and a union branch can be any valid query block including block containing nested UNIONS Additionally different branches of the same union might provide bindings for different variables For example the following query might return a more informative result SELECT name_Alice_knows name_knows_Alice WHERE alice foaf name Alice Palice foaf knows foaf name name_Alice_knows UNION foaf name name_knows_Alice foaf knows alice When applied to the dataset prefix foaf lt http xmlns com foaf 0 1 gt _ alice foaf name Alice foaf knows _ bob _ Cindy _ bob foaf name Bob foaf knows _ alice _ cindy foaf name cindy _ erich foaf name erich foaf knows _ alice will return the following bindings for its SELECT variables name_Alice knows name_knows_ Alice Bob Bob Cindy Erich The empty cells show that certain variables sometimes remain unbound No further processing can be applied to2. 3 1 UNIONS of alternative blocks 3 2 OPTIONAL blocks 3 3 FILTERs 3 5 BIND conditions 3 6 Expressions are explained in 3 4 and lt select spec gt is either a variable or an expression bound to a variable lt select spec gt lt var gt lt expr gt AS lt var gt 3 1 Graph patterns A variable can also be bound in a graph pattern like SELECT person WHERE person foaf name Alice will bind the variable person to all subjects in the triples of the default dataset where the predicate is a URI foaf name and the object is a string Alice and return all those bindings Note this query implies that the prefix foaf is already defined in the session which can be achieved by PREFIX directive PREFIX foaf lt http xmlns com foaf 0 1 gt We can also use a graphical representation of a graph pattern drawing predicates as arrows subjects and objects as graph nodes A node with value provided in the pattern will be shown as rectangle a wildcard node will be depicted as oval with a variable name if provided foaf name A graph pattern may be more complex and contain several variables for example SELECT friend_name WHERE person foaf name Alice person foaf knows friend friend foaf name friend_name Here is used as a conjunction requiring that there should be a triple conforming to each pattern in order for th
3. knows foaf name Bob or graphically foaf name common_friend_name We can use conjunction to indicate that the next triple pattern will have the same subject and predicate SELECT common_friend_name WHERE foaf name common_friend_name foaf knows foaf name Alice foaf name Bob 3 2 Matching alternatives and DISTINCT option Consider that foaf knows relationship is not restricted to be symmetric in the dataset so we would like to trace it in either direction The following query returns names of all the people who know Alice and all people whom Alice knows SELECT friend_name WHERE friend foaf name friend_name alice foaf name Alice alice foaf knows friend UNION friend foaf knows alice This query will effectively express two alternative graph patterns foaf name foaf name foaf name foaf knows foaf knows foaf name friend_name However if foaf knows relationship happens to be mutual in some case same bindings will be generated twice for friend and friend_name To avoid this and return every person at most once we should use DISTINCT option on the freind variable in the SELECT clause SELECT DISTINCT friend friend_name WHERE friend foaf name friend_name alice foaf name Alice alice foaf knows friend UNION friend foaf knows alice
4. them and the result of any expression involving these variables will also be unbound and any filter depending on such an expression will not be satisfied in that case The only exception is the bound function which will return either true or false 3 3 OPTIONAL graph patterns Consider we would like to get the names of all the people Alice knows and also their emails if they are available in the dataset Whenever there is no email information the name of a person should still be returned SELECT friend_name friend_email WHERE foaf name Alice foaf knows friend friend foaf name friend_name OPTIONAL friend foaf email friend_email When applied to the dataset prefix foaf lt http xmlns com foaf 0 1 gt prefix countries lt http example org Countries gt _ alice foaf name Alice foaf knows _ bob cindy 7 _ dave _ bob foaf name Bob foaf email bob example org foaf phone 4912123456789 foaf residesIn countries Germany _ cindy foaf name Cindy foaf phone 46701234567 _ dave foaf name Dave foaf residesIn countries Australia will return the required and the optional bindings friend_name friend_email Bob bob example org Cindy Dave Optional blocks can be nested The nested block will provide new bindings for its variables only if the parent block succeeds In the following query we are interested
5. tt1 true Current dataset i e default graph can be written to a local NTriples file using Dump directive DUMP Current nt You can also load and execute SciSPARQL scripts typically containing function definitions SOURCE directive does exactly that SOURCE talk spargl At any point you can switch to Lisp interpreter using LIsP directive and return to SciSPARQL toploop by evaluating language sparql symbol SPARQL 1 gt lisp Lisp 1 gt language sparql SPARQL 1 gt To exit the toploop use EXIT directctive SPARQL 1 gt exit 2 SPARQL language basics SciSPARQL 1 a superset of SPARQL 1 1 query language which is defined by W3C Recommendations http www w3 org TR sparql1 1 query SciSPARQL complies with lexical specifications for the basic terms like URIs Literals Variables and Bank Nodes The following chapters of the document can be used as a documentation for SciSPARQL language 4 8 10 1 11 15 3 1 16 1 Chapters 17 19 give a more formal definition of the language syntax and semantics 2 1 Lexical definitions A token in SciSPARQL is either a syntactic delimiter one of an operator one of l lt lt gt gt amp amp a keyword followed by a whitespace or a delimiter a numeric literal like 2 3 14 4 3e10 folowed by a whitespace a delimiter or an operator adate amp time literal like a string literal enclosed in si
6. RI values are comparable with operands of the same type Boolean operators include I amp amp and operate on effective boolean values that can be derived from operands of any type Effective boolean values of non boolean types are described in the following table type effective boolean value xsd integer xsd float false if equal to 0 true otherwise xsd double xsd string false if empty true otherwise xsd dateTime always true URI always true other false if string part is empty true otherwise 3 4 3 Handling of unbound values If a variable is unbound e g due to its binding in an OPTIONAL graph pattern the result of any expression involving that variable is also unbound The exception are the boolean operators and that implement the following three value logic according to W3C SPARQL specifications A B AllB AccB true true true true true false true false false true true false false false false false true unbound true unbound unbound true true unbound false unbound unbound false unbound false unbound false unbound unbound unbound unbound Most built in and all foreign functions are also not applicable to the unbound values effectively returning unbound result The only exception is bound function that will return false if the argument is unbound If the operator is not applicable to the va
7. SciSPARQL User s Manual Andrej Andrejev 2012 06 07 Uppsala DataBase Laboratory Department of Information Technology Uppsala University Sweden Summary Acknowledgements 1 Getting started SciSPARQL is implemented with SSDM technically an extension of Amos II system It is being distributed together with Amos II executables headers and documentation The following files belong to SSDM extension proper bin ssdm dll bin ssdm dmp bin ssdm cmd ssdm To run SSDM use bin ssdm cmd batch file Directory bin should be current or listed in system PATH The SciSPARQL toploop When started the system enters an Amos II top loop where it reads SciSPARQL statements including queries function calls and system directives executes them and prints their results The prompter in the SciSPARQL top loop is SciSPARQL n gt where n is a generation number The generation number is increased every time a SciSPARQL statement is executed Typically you start by loading data Loap directive allows loading local or remote Turtle or NTriples files containing RDF datasets Unqualified filename is processed relative to the current directory LOAD talk tt1l The files are loaded into the default graph Multiple files can be loaded and any RDF blank nodes used in the different datasets become renamed to keep them lexically distinct To empty the default graph before loading use LOAD with true as a second argument LOAD talk
8. e variable binding to be valid Note that not all the variables are interesting for us only the bindings of friend_name are returned This query can be simplified in several ways 1 We can use instead of to indicate that the next pattern will have the same subject SELECT friend_name WHERE person foaf name Alice foaf knows friend friend foaf name friend_name 2 Since we are not interested in bindings for person we do not need to provide a variable name instead we can tell the parser to generate a wildcard by using an unlabeled blank node in the query SELECT friend_name WHERE foaf name Alice foaf knows friend friend foaf name friend_name 3 We can get rid of riend variable as well by substituting it with a blank subject construct SELECT friend_name WHERE foaf name Alice foaf knows foaf name friend_name The foaf name friend_name construct denotes a wildcard subject of a triple pattern with specified predicate and object and can be used as a blank node anywhere in a graph pattern So this graph pattern will contain two unnamed blank nodes foaf name i friend_name Another query will look for names of the people who know both Alice and Bob SELECT common_friend_name WHERE foaf name common_friend_name foaf knows foaf name Alice foaf
9. iable see below followed by a whitespace a delimiter or an operator A labelled blank node see below followed by a whitespace a delimiter or an operator An identifier in SciSPARQL is a sequence of letters digits and numbers where the first character is a letter Identifiers are used to form variables blank node labels prefixes and function names Variables in W3C SPARQL and SciSPARQL start with variable marker or followed by an identifier The variable marker is not a part of its name so abc and Sabc are different occurrences of the same variable Labelled blank nodes in W3C SPARQL and SciSPARQL start with _ followed by identifier There is also syntax for implicit blank nodes like where unique labels are generated by the parser Prefixes in W3C SPARQL and SciSPARQL consist of an identifier followed by or just which corresponds to an empty identifier Prefixes are declared in the beginning of a query or in separate SciSPARQL statemens and are used to abbreviate URIs All W3C SPARQL and SciSPARQL identifiers and keywords are defined as case insensitive except for keyword a which can be only used in lowercase 2 2 Comments and whitespaces Comments start with and follow to the end of line anywhere inside or outside a query In all cases end of line character is used as a whitespace delimiter equivalent to space and tab so the comment also becomes a whitespace There is no other syntactic
10. in the country information only if a phone number is returned SELECT friend_name friend_phone friend_country WHERE foaf name Alice foaf knows friend friend foaf name friend_name OPTIONAL friend foaf phone friend_phone OPTIONAL friend foaf residesIn friend_country When applied to the same dataset this query returns friend_name friend_phone friend_country Bob 4912123456789 countries Germany Cindy 46701234567 Dave Note that the there is no country information returned for Dave since there is no his phone of in the dataset There can also be several successive OPTIONAL blocks in a query block and some of them might attempt to bind the same variable In this case the OPTIONAL block that appears earlier in the query gets the priority Consider the following query where we are interested in the contact information Alice s friends preferably an email a phone number or nothing but the name SELECT friend_name friend_contact WHERE foaf name Alice foaf knows friend friend foaf name friend_name OPTIONAL friend foaf email friend_contact OPTIONAL friend foaf phone friend_contact Applied to the same dataset the query will return friend_ name friend_contact Bob bob example org Cindy 46701234567 Dave If we swap the two OPTIONAL block
11. lues of its operands like comparing a number to a string or applying the operator produces arithmetic error like dividing by zero no error is raised and the result is also unbound Unbound values can be seen as empty cells in SELECT query results n CONSTRUCT queries resulting triples with unbound terms are filtered out FILTER and HAVING conditions do not distinguish between unbound and effective boolean false results of their expressions 3 4 4 Function calls and typecasting
12. ngle or double quotes like one 1 Quotes of the same type appearing inside the string and the backslash character should be escaped with backslash This string contains double quote and backslash No other escapes are supported in SciSPARQL strings instead tab and newline characters can be included directly into a string This string is a paragraph a language and locale tag starting with like En Us Technically any string is valid as a tag in SciSPARQL and it is stored as part of a string literal that it syntactically follows a Uniform Resource Identifier URI enclosed in angular brackets lt gt like lt http example org gt The first character following the opening bracket should be a letter Angular bracket percent s space tab and newline characters inside URI should be escaped i e replaced with 3 followed by hexadecimal ASCII code of that character for example lt http example org do bml param 3Cempt y 3E gt an abbreviated URI consisting of a prefix see below followed by URI local part like rdf type Any non alphanumeric characters in the URI local part should be escaped as in URI The only exceptions are and _ characters anywhere in the local part and dot if not on the last position A function call consisting of a URI an abbreviated URI or an identifier see below directly followed by an opening parenthesis A var
13. role associated with newline so the query can be split into lines in any arbitrary way as long as the tokens remain in one piece This means that a comment can be inserted after any token 2 3 Queries A query is a syntactically valid sequence of tokens optionally followed by delimiter When queries are processed in toploop or stored in sparq file delimeter is required to separate the queries W3C SPARQL defines 4 types of queries SELECT CONSTRUCT DESCRIBE and ASK each starting with a corresponding keyword and optionally preceded by PREFIX and or BASE clauses Currently SciSPARQL supports only SELECT Chapter 3 and CONSTRUCT Chapter 4 queries and PREFIX clause It also adds DEFINE Chapter 5 PREFIX LISP and EXIT directives and any function call can be used as a query 3 SELECT querying for values The most simple query will have to bind a value to a resulting variable SELECT 1 as res Will return res 1 In the most general form a SciSPARQL select query has the following syntax PREFIX lt prefix gt lt URI gt SELECT DISTINCT lt select spec gt FROM lt graph id gt WHERE lt block gt GROUP BY lt var gt HAVING lt expr gt lt select spec gt lt var gt lt expr gt AS lt var gt lt block gt is an enclosed in curly braces dot separated conjunction of different kinds of conditions namely graph patterns
14. s in this query a phone number would be returned for Bob as well 3 4 Expressions Logical and arithmetic expressions in SciSPARQL are formed by terms and operators Terms can be numeric string or typed literals URIs keywords true and false representing logical values variables function calls and typecasting array dereferences 3 4 1 Typed literals Typed literals are syntactically formed by a string followed by delimiter and a complete or abbreviated URI indicating its type for example 1 44xsd integer 10101110 lt http example org types MyBitVector gt 2005 02 28T00 00 00Z2 xsd dateTime The typed literals of type xsd integer xsd float xsd string xsd double xsd dateTime and xsd boolean found in SciSPARQL queries as well as in the imported Turtle NTriples files are automatically converted to corresponding simple values Other typed literals are stored together with their type URI and are considered comparable and equal when both the type URIs and value strings are the same 3 4 2 Operators Arithmetic operators are and are only applicable to numbers Comparison operators include lt lt gt gt that are only applicable if both operands are numbers or both are strings and that are applicable to the operands of comparable types All numeric types are comparable with each other typed literals are only comparable when they are completely equal strings dataTime boolean and U
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