SPARQL in a nutshell
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SPARQL is a query language, result format, and access protocol for querying and accessing RDF data. SPARQL queries use a SELECT-FROM-WHERE structure to match triple patterns against RDF graphs. The WHERE clause contains a conjunction of triple patterns that can be extended with filters, optional patterns, and unions of patterns. SPARQL results are returned in an XML format and the protocol defines HTTP and SOAP bindings for sending queries and receiving results over the web.
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SPARQL in a nutshell
- 1. S PAR QL in a nutshell fabien, gandon, inria
- 2. RDF triple model is the first layer of the semantic web standards
- 3. SPARQL on top... an R D F query language and data access protocol
- 4. SPARQL stands for S PARQL P rotocol and R DF Q uery L anguage
- 5. SPARQL in 3 parts part 1: query language part 2: result format part 3: access protocol
- 6. SPARQL query SELECT ... FROM ... WHERE { ... }
- 7. SELECT clause to identify the values to be returned
- 8. FROM clause to identify the data sources to query
- 9. WHERE clause the triple/graph pattern to be matched against the triples/graphs of RDF
- 10. WHERE clause a conjunction of triples: { ?x rdf:type ex:Person ?x ex:name ?name }
- 11. PREFIX to declare the schema used in the query
- 12. example persons and their names PREFIX ex: < http://inria.fr/schema# > SELECT ?person ?name WHERE { ?person rdf:type ex:Person ?person ex:name ?name . }
- 13. example of result <?xml version="1.0"?> <sparql xmlns="http://www.w3.org/2005/sparql-results#" > <head> <variable name=" person "/> <variable name=" name "/> </head> <results ordered="false" distinct="false"> <result> <binding name=" person "> <uri>http://inria.fr/schema#fg</uri> </binding> <binding name=" name "> <literal>gandon</literal> </binding> </result> <result> ...
- 14. FILTER to add constraints to the graph pattern (e.g., numerical like X>17 )
- 15. example persons at least 18-year old PREFIX ex: < http://inria.fr/schema# > SELECT ?person ?name WHERE { ?person rdf:type ex:Person ?person ex:name ?name . ?person ex:age ?age . FILTER (?age > 17) }
- 16. FILTER can use many operators, functions (e.g., regular expressions), and even users' extensions
- 17. OPTIONAL to make the matching of a part of the pattern optional
- 18. example retrieve the age if available PREFIX ex: < http://inria.fr/schema# > SELECT ?person ?name ?age WHERE { ?person rdf:type ex:Person ?person ex:name ?name . OPTIONAL { ?person ex:age ?age } }
- 19. UNION to give alternative patterns in a query
- 20. example explicit or implicit adults PREFIX ex: < http://inria.fr/schema# > SELECT ?name WHERE { ?person ex:name ?name . { { ?person rdf:type ex:Adult } UNION { ?person ex:age ?age FILTER (?age > 17) } } }
- 21. Sequence & modify ORDER BY to sort LIMIT result number OFFSET rank of first result
- 22. example results 21 to 40 ordered by name PREFIX ex: < http://inria.fr/schema# > SELECT ?person ?name WHERE { ?person rdf:type ex:Person ?person ex:name ?name . } ORDER BY ?name LIMIT 20 OFFSET 20
- 23. UNBOUND test a variable is not bound ; used for negation as failure
- 24. example persons who are not known authors PREFIX ex: < http://inria.fr/schema# > SELECT ?name WHERE { ?person ex:name ?name . OPTIONAL { ?person ex:author ?x } FILTER ( ! bound(?x) ) }
- 25. negation is tricky and errors can easily be made.
- 26. ? does this find persons who do not know "java" ? PREFIX ex: < http://inria.fr/schema# > SELECT ?name WHERE { ?person ex:name ?name . ?person ex:knows ?x FILTER ( ?x != "Java " ) }
- 27. NO! also persons who know something else ! PREFIX ex: < http://inria.fr/schema# > SELECT ?name WHERE { ?person ex:name ?name . ?person ex:knows ?x FILTER ( ?x != "Java" ) } fabien ex:knows "Java" fabien ex:knows "C++" fabien is a answer...
- 28. YES! persons who are not known to know "java" ... negation of an option... PREFIX ex: < http://inria.fr/schema# > SELECT ?name WHERE { ?person ex:name ?name . OPTIONAL { ?person ex:knows ?x FILTER ( ?x = "Java" ) } FILTER ( ! bound(?x) ) }
- 29. ASK to check just if there is at least one answer ; result is "true" or "false"
- 30. example is there a person older than 17 ? PREFIX ex: < http://inria.fr/schema# > ASK { ?person ex:age ?age FILTER (?age > 17) }
- 31. CONSTRUCT return a specific RDF graph for each result
- 32. example return instances of adults for persons older than 17 PREFIX ex: < http://inria.fr/schema# > CONSTRUCT { ?person rdf:type ex:Adult } WHERE { ?person ex:age ?age FILTER (?age > 17) }
- 33. SPARQL protocol sending queries and their results accross the web
- 34. example with HTTP Binding GET /sparql/?query= <encoded query> HTTP/1.1 Host: www.inria.fr User-agent: my-sparql-client/0.1
- 35. example with SOAP Binding <?xml version="1.0" encoding="UTF-8"?> <soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" > <soapenv:Body> <query-request xmlns="http://www.w3.org/2005/09/sparql-protocol-types/#" > <query>SELECT ?x ?p ?y WHERE {?x ?p ?y}</query> </query-request> </soapenv:Body> </soapenv:Envelope>
- 36. Take-away summary of SPARQL
- 37. SPARQL is... ... a query language ... ... a result format ... ... an access protocol ... ... for RDF
- 38. SPARQL query language based on the triple model ?x ?p ?y filters to add constraints optional parts and alternative parts
- 39. fabien, gandon