Semantic Web: Formalisms, SPARQL, and Query Solutions

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Explore the concepts of Semantic Web formalisms, SPARQL query language, and query solutions, including examples and the WHERE clause. Learn about querying techniques and sub-graph matching to retrieve relevant data efficiently in a distributed environment.

  • Semantic Web
  • SPARQL
  • Query Solutions
  • Web Semantics
  • RDF
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  1. M2 DSC UE2 Semantic Web http://ci.mines-stetienne.fr/cours/2017/dsc-websem/ 4. Querying Maxime Lefran ois maxime.lefrancois@emse.fr Freely adapted from presentations of Lynda Temal, https://fr.linkedin.com/in/lynda-temal-32a206a/fr Which were themselves freely adapted from presentations of Fabien Gandon, Inria. 1

  2. Semantic Web Formalisms Trust 2

  3. SPARQL A common distributed query language SPARQL = SPARQL Protocol and RDF Query Language SPARQL 1.1: W3C Standard 2013 - SPARQL Query Language - SPARQL Update - SPARQL Protocol (over HTTP) 3

  4. One example @prefix foaf: <http://xmlns.com/foaf/0.1/> . @base <http://example.org/> <Alice> foaf:name "Alice" ; foaf:lastName Smith" . <John> foaf:firstName Smith" . _:bn1 foaf:name "Bob" . PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?name WHERE { ?x foaf:name ?name } ?x <http://example.org/Alice> _:a ?name Alice Bob 4

  5. SPARQL Query: four types of queries PREFIX foaf: <http://xmlns.com/foaf/0.1/> ASK WHERE { ?x foaf:name ?name } PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?name WHERE { ?x foaf:name ?name } PREFIX foaf: <http://xmlns.com/foaf/0.1/> CONSTRUCT { ?x a foaf:Person } WHERE { ?x foaf:name ?name } PREFIX foaf: <http://xmlns.com/foaf/0.1/> DESCRIBE ?x WHERE { ?x a foaf:Person } 5

  6. The WHERE clause The simplest where clause consists of a Basic Graph Patterns = a RDF Graph with variables PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT * WHERE { ?x foaf:knows ?y . ?y vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue ?tel ] . } 6

  7. Query solutions Search for sub-graphs that match the query -> return values for the different variables (uri, blank node, or literal) @prefix foaf: <http://xmlns.com/foaf/0.1/> . @base <http://example.org/> . <Paul> vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33610..." ] ; foaf:knows <Bob>, <Alex> . <Bob> vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33620..." ] ; foaf:knows <Paul>, <Cathia> . PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?y WHERE { ?x foaf:knows ?y . ?y vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue ?tel ] . <Cathia> vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33630..." ] ; vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33640..." ] . } 7

  8. Query solutions What changes in the query solutions ? @prefix foaf: <http://xmlns.com/foaf/0.1/> . @base <http://example.org/> . <Paul> vcard:hasTelephone [ vcard:hasValue "+33610..." ] ; foaf:knows <Bob>, <Alex> . <Bob> vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33620..." ] ; foaf:knows <Paul>, <Cathia> . PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT * WHERE { ?x foaf:knows ?y . ?y vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue ?tel ] . < Cathia > vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33630..." ] ; vcard:hasTelephone [ a vcard:Voice ; vcard:hasValue "+33640..." ] . } 8

  9. SELECT Queries Output of SELECT queries as XML <?xml version="1.0"?> <sparql xmlns="http://www.w3.org/2005/sparql-results#"> <head> <variable name="x"/> <variable name= y"/> <variable name= tel"/> </head> <results> <result> <binding name="x"><uri>http://example.org/Paul</uri></binding> <binding name= y"><uri>http://example.org/Bob</uri></binding> <binding name= tel"><literal>+33620... </literal></binding> </result> </sparql> 9

  10. SELECT Queries Output of SELECT queries as JSON { "head": { "vars": [ "x" , "y" , "tel" ] } , "results": { "bindings": [ { "x": { "type": "uri" , "value": "http://example.org/Paul" } , "y": { "type": "uri" , "value": "http://example.org/Bob" } , "tel": { "type": "literal" , "value": "+33620... " } } , ... ] } } 10

  11. ASK Queries Output of a ASK query as XML <sparql xmlns="http://www.w3.org/2005/sparql-results#"> <head></head> <boolean>true</boolean> </sparql> OR <sparql xmlns="http://www.w3.org/2005/sparql-results#"> <head></head> <boolean>false</boolean> </sparql> Output of a ASK query as JSON { { "head" : { } , "boolean" : true "head" : { } , "boolean" : false OR } } 11

  12. CONSTRUCT Queries Output of a CONSTRUCT query: RDF (has different serializations) 12

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