Advanced SPARQL Techniques and Examples

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Explore advanced SPARQL techniques, including expressions in selections, value assignments, aggregates, and more. Dive into practical examples that demonstrate the power and versatility of SPARQL in semantic technologies.

  • SPARQL
  • Semantic Technologies
  • Examples
  • Aggregates
  • Query
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  1. Part 7 SPARQL 1.1 SPARQL 1.1 Werner Nutt Semantic Technologies 1 Master Informatique

  2. Part 7 SPARQL 1.1 Acknowledgment These slides are essentially identical with those by Sebastian Rudolph for his course on Semantic Web Technologies at TU Dresden Semantic Technologies 2 Master Informatique

  3. Part 7 SPARQL 1.1 Expressions in the Selection and Bindings Solutions can be extended by evaluated expressions with (expression AS ?var) used for the assignment: in the SELECT clause in the GROUP BY clause within BIND in a group graph pattern Solutions from a group can further be joined with solutions given via a VALUES pattern Semantic Technologies 3 Master Informatique

  4. Part 7 SPARQL 1.1 Example BIND (without Prefix Declarations) Data ex:Book ex:title ex:price ex:discount 10 . "SPARQL Tutorial" ; 42 ; Query SELECT ?title ?price WHERE { ?b ex:title ?title; ex:price ?p ; ex:discount ?r BIND ((?p-?r) AS ?price) } Result ?title "SPARQL Tutorial", ?price 32 Algebra: Extend(Bgp(...), ?price, (?p-?r)) Semantic Technologies 4 Master Informatique

  5. Part 7 SPARQL 1.1 Example SELECT Expressions (without Prefix Declarations) ex:Book ex:title "SPARQL Tutorial" ; ex:price 42 ; ex:discount 10 . Data Query SELECT ?title ((?p-?r) AS ?price WHERE { ?b ex:title ?title; ex:price ?p ; ex:discount ?r } Result ?title "SPARQL Tutorial", ?price 32 Algebra: Extend(Bgp(...), ?price, (?p-?r)) Semantic Technologies 5 Master Informatique

  6. Part 7 SPARQL 1.1 Example VALUES Data ex:Book1 ex:Book2 ex:title ex:title "SPARQL Tutorial". "SemWeb". Query SELECT ?title WHERE { ?b ex:title ?title VALUES ?b { ex:Book1 } } Result ?title "SPARQL Tutorial Bindings are conjunctively joined Semantic Technologies 6 Master Informatique

  7. Part 7 SPARQL 1.1 Aggregates Aggregates allow for the grouping of solutions and the computation of values over the groups Example Query SELECT ?lecture (COUNT(?student) AS ?c) WHERE { ?student ex:attends ?lecture } GROUP BY ?lecture HAVING COUNT(?student) > 5 GROUP BY groups the solutions (here into students who attend the same lecture) COUNT is an aggregate function that counts the solutions within a group (here the number of students in the lecture) HAVING filters aggregated values Semantic Technologies 7 Master Informatique

  8. Part 7 SPARQL 1.1 Aggregates in SPARQL 1.1 SPARQL 1.1 supports the following aggregate functions, which are evaluated over the values in a group: COUNT counts the solutions MIN finds the minimal value MAX finds the maximal value SUM sums up the values AVG computes the average SAMPLE picks a random value GROUP_CONCAT string concatenation, Example: GROUP_CONCAT(?x ; separator = ",") Note: Most SPARQL 1.1 implementations only concatenate strings! Semantic Technologies 8 Master Informatique

  9. Part 7 SPARQL 1.1 Exercise Aggregates Data ex:Paul ex:hasMark 28.0 . ex:Paul ex:hasMark 24.0 . ex:Mary ex:hasMark 25.0 . ex:Peter ex:hasMark 22.0 . Return those students (with their average marks) that have an average mark > 25. Return the subgraph of the data consisting of students with an average mark > 25 and their marks. Return those that have an average mark > 25 together with a list of their marks, separated by | . Show also what you expect to be the solution. Semantic Technologies 9 Master Informatique

  10. Part 7 SPARQL 1.1 Subqueries Example Query SELECT ?name WHERE { ?x foaf:name ?name . { SELECT ?x (COUNT(*) AS ?count) WHERE { ?x foaf:knows ?y . } GROUP BY ?x HAVING (?count >= 3) } } Results for the inner query are conjunctively joined with the results of the outer query Semantic Technologies 10 Master Informatique

  11. Part 7 SPARQL 1.1 Negation in Queries Two forms of negation with conceptual and small semantic differences Test for non-matches for a pattern Removal of matching solutions Filter SELECT ?x WHERE { ?x rdf:type foaf:Person . FILTER NOT EXISTS { ?x foaf:name ?name } } Minus SELECT ?x WHERE { ?x rdf:type foaf:Person . MINUS { ?x foaf:name ?name } } What are the corresponding constructs in SQL? What is the difference between them in SQL? Semantic Technologies 11 Master Informatique

  12. Part 7 SPARQL 1.1 Evaluation of Negation via Filter Data _:x rdf:type foaf:Person . _:x foaf:name "Peter" . _:y rdf:type foaf:Person . Query Pattern { ?x rdf:type foaf:Person . FILTER NOT EXISTS { ?x foaf:name ?name } } [[ Bgp(1st Pattern) ]]G : 1: ?x _:x, 2: ?x _:y For each solution, we instantiate the second pattern Solution is removed if the instantiated pattern matches ( 1) otherwise we keep the solution ( 2) Semantic Technologies 12 Master Informatique

  13. Part 7 SPARQL 1.1 Evaluation of Negation via Minus Data _:x rdf:type foaf:Person . _:x foaf:name "Peter" . _:y rdf:type foaf:Person . Query Pattern { ?x rdf:type foaf:Person . MINUS { ?x foaf:name ?name } } [[ Bgp(1st Pattern) ]]G : 1= { 1: ?x _:x, 2: ?x _:y } [[ Bgp(2nd Pattern) ]]G : 2= { 3: ?x _:x, ?name "Peter } Minus( 1, 2) = { | 1 and 2 : and incompatible or dom( ) dom( ) = } 1 ! : 1 compatible with 3 and has non-disjoint domain 2 : 2 incompatible with 3 Semantic Technologies 13 Master Informatique

  14. Part 7 SPARQL 1.1 Minus and Filter Negation: Differences Data ex:a ex:b ex:c . Query Pattern { ?s ?p ?o FILTER NOT EXISTS { ?x ?y ?z } } Filter pattern matches always (variables disjoint) every solution is removed Query Pattern { ?s ?p ?o MINUS { ?x ?y ?z } } Minus does not remove any solutions since the domain of the solutions is disjoint Semantic Technologies 14 Master Informatique

  15. Part 7 SPARQL 1.1 Regular Expressions in Patterns Property paths are constructed using regular expressions over predicates Sequence of paths: Optional path: Paths with arbitrary length: Alternative paths: Inverse paths: Negation of paths: ?s ex:p1/ex:p2 ?o ?s ex:p? ?o ?s ex:p+ ?o, ?s ex:p* ?o ?s (ex:p1|ex:p2) ?o ?s ex:p ?o same as ?o ex:p ?s ?s !ex:p ?o A negation of path expression !ex:p matches a path that does not have predicate ex:p Semantic Technologies 15 Master Informatique

  16. Part 7 SPARQL 1.1 Regular Expressions in Patterns Property paths are, where possible, translated into standard SPARQL constructs Examples? Some new operators are still necessary Semantic Technologies 16 Master Informatique

  17. Part 7 SPARQL 1.1 Property Path Examples Example Query 1 PREFIX ... SELECT ?xName WHERE { ?x rdf:type foaf:Person . ?x foaf:name ?xName ?x foaf:knows/foaf:knows/foaf:name "Bill Gates" . } Example Query 2 PREFIX ... SELECT ?s WHERE { ?s rdf:type ?type . ?type rdfs:subClassOf* ex:SomeClass . } Semantic Technologies 17 Master Informatique

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