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SQWRL: a Query Language for OWL

SQWRL: a Query Language for OWL . Martin O’Connor, Amar Das Stanford Center for Biomedical Informatics Research, Stanford University. SWRL and Querying. SWRL is a rule language, not a query language However, a rule antecedent can be viewed as a pattern matching specification, i.e., a query

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SQWRL: a Query Language for OWL

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  1. SQWRL: a Query Language for OWL Martin O’Connor, Amar Das Stanford Center for Biomedical Informatics Research, Stanford University

  2. SWRL and Querying SWRL is a rule language, not a query language However, a rule antecedent can be viewed as a pattern matching specification, i.e., a query With built-ins, language compliant query extensions are possible Hence: SQWRL (Semantic Query-Enhanced Web Rule Language; pronounced squirrel)

  3. Example SWRL Rule: is adult? Person(?p) ^ hasAge(?p,?age) ^ swrlb:greaterThan(?age,17) → Adult(?p) Classify all persons in an ontology with an age greater than 17 as adults.

  4. Example SQWRL Query Person(?p) ^ hasAge(?p,?age) ^ swrlb:greaterThan(?age,17) → sqwrl:select(?p, ?age) List all persons in an ontology with an age greater than 17.

  5. Person(?p) ^ hasAge(?p,?age) ^ swrlb:greaterThan(?age,17) → sqwrl:select(?p, ?age) ^ sqwrl:orderBy(?age) Example SQWRL Query:Ordering Results List all persons in an ontology with an age greater than 17 and order the result by age in ascending order. Also: orderByDecending

  6. Example SQWRL Query:Counting Results Count all cars in ontology. Car(?c) → sqwrl:count(?c) Important: no way of asserting count in ontology!

  7. Person(?p) ^ hasAge(?p, ?age) →sqwrl:avg(?age) Example SQWRL Query:Aggregating Results Average age of persons in ontology. Also: sqwrl:max, sqwrl:min, sqwrl:sum

  8. Example SQWRL Query: Arbitrary OWL Class Expressions (hasChild >= 1)(?x) → sqwrl:select(?x) Individuals with cardinality restrictions. SQWRL can act as a DL query language

  9. Semantics (Briefly) Any SWRL body is valid query specification Does not violate OWA Does assume UNA

  10. Useful but Relatively Inexpressive Useful but relatively inexpressive. Needs: Negation As Failure Disjunction Complex Counting Complex Aggregation We have recently added sets to the language to tackle these problems

  11. SQWRL: Basic Set Operator Count all persons in ontology. Person(?p) ° sqwrl:makeSet(?s, ?p) ^ sqwrl:size(?size, ?s) → sqwrl:select(?size) Ser operators: sqwrl:isEmpty, sqwrl:union, sqwrl:difference

  12. SQWRL: Negation as Failure List the number of non beta blocker drugs in ontology. Drug(?d) ^ BetaBlocker(?b) ° sqwrl:makeSet(?s1, ?d) ^ sqwrl:makeSet(?s2, ?b) ^ sqwrl:difference(?s3, ?s1, ?s2) ^ sqwrl:size(?size, ?s3) → sqwrl:select(?size)

  13. SQWRL: Disjunction List the number of beta blocker or anti-hypertensive drugs in ontology. AntiHypertensive(?d1) ^ BetaBlocker(?d2) ° sqwrl:makeSet(?s1, ?d1) ^ sqwrl:makeSet(?s2, ?d2) ^ sqwrl:union(?s3, ?s1, ?s2) ^ sqwrl:size(?size, ?s3) → sqwrl:select(?size)

  14. SQWRL: Complex Counting List all patients on more than two drugs. Patient(?p) ^ hasDrug(?p,?d) ° sqwrl:makeSet(?s, ?d) ^ sqwrl:groupBy(?s, ?p) ^ sqwrl:size(?n, ?s) ^ swrlb:greaterThan(?n, 2) → sqwrl:select(?p)

  15. SQWRL: Complex Aggregation List the average dose of each drug taken by each patient. Patient(?p) ^ hasDrug(?p,?d) ^ hasDose(?d, ?dose) ° sqwrl:makeSet(?s, ?dose) ^ sqwrl:groupBy(?s, ?p, ?d) ^ sqwrl:avg(?avg, ?s) → sqwrl:select(?p, ?d, ?avg)

  16. SQWRL: NAF, Disjunction, Complex Counting and Aggregation List the average dose of patients that are on more than two drugs and where none of those drugs is a beta blocker or anti-hypertensive. Patient(?p) ^ hasDrug(?p,?d) ^ hasDose(?d, ?dose) ^ BetaBlocker(?d1) ^ AntiHypertensive(?d2) ° sqwrl:makeSet(?s1, ?dose) ^ sqwrl:groupBy(?s1, ?p, ?d) ^ sqwrl:makeSet(?s2, ?drug) ^ sqwrl:groupBy(?s2, ?p) ^ sqwrl:makeSet(?s3, ?d1, ?d2) ^ sqwrl:avg(?avg, ?s1) ^ sqwrl:size(?n, ?s2) ^ swrlb:greaterThan(?n, 2) ^ sqwrl:intersection(?s4, ?s2, ?s3) ^ sqwrl:isEmpty(?s4) → sqwrl:select(?p, ?d, ?avg)

  17. Advantages of SWRL-Based Query Language • No need to invent a new semantics • Standard(ish) presentation syntax (° is syntactic sugar) • Standard serialization • Can use existing reasoning infrastructure • Can use existing editors • On-the-fly query checking in editors • For SWRL users, easy to learn • Extensible with built-ins (TBox, RDF,XML…) • Useful for debugging SWRL rules • Queries can interoperate with rules • Not SPARQL!

  18. Summary • Core language features available for 1+ years in Protege-OWL • Set operators will be available in month or so • Plans for Protege4 port

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