SWT Lecture Session 8 - Rules

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  • soundness, completeness, termintion
  • soundness, completeness, termintion
  • soundness, completeness, termintion
  • soundness, completeness, termintion
  • SWT Lecture Session 8 - Rules

    1. 1. + Rules Mariano Rodriguez-Muro, Free University of Bozen-Bolzano
    2. 2. + Disclaimer  License  This work is licensed under a Creative Commons Attribution-Share Alike 3.0 License (http://creativecommons.org/licenses/by-sa/3.0/)
    3. 3. + Reading material  Chapter 7. Semantic Web Programming  Chapter 6. Foundations of Semantic Web.
    4. 4. + What are rules  Means of representing knowledge  An ontology language  Can be seen as conditions statements: if [] then []  if x is a Man and x hasChild y Father(x)
    5. 5. + Why rules  Easy to understand  RDFS (and sometimes OWL) is not enough: If a person x is the brother of somebody y, and there is z such that z is the uncle of x, then z is the uncle of y too. for all x,y,z, if hasBrother(x,y) & hasUncle(x,z) then hasUncle(y,z)
    6. 6. + SWRL
    7. 7. + 7 SWRL  How can datalog and OWL be combined?  SWRL – Semantic Web Rule Language [swirl] • Proposal for a rule based Semantic Web Language (W3C member submission) http://www.w3.org/Submission/SWRL/ • Idea: datalog rules referring to RDF classes/properties Symbols in rules can be OWL identifiers or new symbols • Various further features and syntactic forms • Support in inference engines (very wide spread support)
    8. 8. + SWRL Syntaxes  Two syntaxes: 1. Abstract syntax based on “Extended Backus-Naur Form notation 1. Directly translatable to a Human readable syntax (SPARQL lie) 2. XML Concrete Syntax 1. Parsable by existing OWL/RDF/XML parsers 2. Suitable as a exchange language for the semantic web
    9. 9. + Abstract Syntax
    10. 10. + Abstract Syntax Example For the rule: The corresponding abstract syntax:
    11. 11. + Example 1 A very common use for rules is to move property values from one individual to a related individual Express the fact that the style of an art object is the same as the style of the creator. Artist(?x) & artistStyle(?x,?y) & Style(?y) & creator(?z,?x) ⇒ style/period(?z,?y) Implies(Antecedent(Artist(I-variable(x)) artistStyle(I-variable(x) I-variable(y)) Style(I-variable(y)) creator(I-variable(z) I-variable(x))) Consequent(style/period(I-variable(z) I-variable(y))))
    12. 12. + RDFS as rules  Provide a translation of all RDFS axiom as rules  subClassOf  subPropertyOf  domain  range
    13. 13. + Beyond RDFS  Transitivity of a property P  Reflexivity of a property P  Inverse of a property P  Equivalence of properties/classes  Sufficient conditions for class membership
    14. 14. + Built ins  One of the main motivations for SWRL rules  Provide means to manipulate data  Comparisons  Mathematical transformations  List operators  Modifiers for strings, dates and times  Boolean and URI checks  URI construction
    15. 15. + Built-ins examples hasAddress(?creditCardMachine, ?ccAddress) ^ hasAddress(?customer, ?custAddress) ^ hasState(?ccAddress, ?ccState) ^ hasState(?custAddress, ?custState) ^ swrlb:equal(?custState, ?ccState) ^ hasBirthday(?customer, ?bDate) ^ swrlb:subtractYearMonthDurations(?diff, ?today, ?bDate) ^ swrlb:greaterThanOrEqual(?diff, "P18Y0M") → LegalCigaretteBuyer(?customer)
    16. 16. + Built-ins examples foaf:Person(?person) ^ foaf:gender(?person, "female") ^ foaf:name(?person, ?name) → swrlb:stringConcat(?s, "Dear Ms. ", ?name, ":") ^ hasFormalGreeting(?person, ?s)
    17. 17. + Empty antecedents/consequent  Empty antecedent indicate the consequent is ALWAYS true  State class/property disjointness  Empty consequents indicate the antecedent is a contradiction  State a FK-like constraint  State number-restriction constraints  Allow to define FACTs and CONSTRAINTS
    18. 18. + XML Concrete Syntax • Based on OWL XML Presentation Syntax and RuleML • The SWRL XML syntax uses the OWL XML Ontology root element and some of its subelements: • VersionInfo • PriorVersion • BackwardCompatibleWith • IncompatibleWith • Imports • Annotation • Class • EnumeratedClass •SubClassOf •EquivalentClasses •DisjointClasses •DatatypeProperty •ObjectProperty •SubPropertyOf •EquivalentProperties •Individual •SameIndividual •DifferentIndividuals
    19. 19. + XML Elements (1) • VAR • IMP
    20. 20. + XML Element (2) • Rlab • Body • Head
    21. 21. + XML Elements (cont) • classAtom
    22. 22. + XML Elements (cont) • datarangeAtom
    23. 23. + XML Elements (cont) • individualPropertyAxiom
    24. 24. + XML Elements (cont) • datavaluedPropertyAxiom
    25. 25. + XML Elements (cont) • sameIndividualAtom
    26. 26. + XML Elements (cont) • differentIndividualsAtom
    27. 27. + XML Elements (cont) • builtInAtom  Built in atoms include: Comparison, Mathematical transformations, List operators, Modifiers for strings, dates and times, Boolean and URI checks, URI constructions
    28. 28. + When RDFS/Rules RDFS/OWL  Expressivity for RDFS/OWL is enough  Use is knowledge sharing  Application requires high performance/uses specialized reasoner  Application requires standard behavior Rules  Expressivity only captures by rules  Use is application behavior  Application requires complex reasoning  Application relies on a particular inference engine only
    29. 29. + Conclusion  Rules are a VERY expressive (powerful) ontology language  Rules can capture most inferences provided by RDFS (part of OWL too)  Rules shouldn’t be abused. Performance of rule based reasoning is suboptimal w.r.t. RDFS/OWL specialized reasoning.  Rules can be a powerful mean to capture application behiavor.  Note, although SWRL is the defacto rule language for the semantic web, there are new standards, i.e. RIF, that might take over in the future (further information in FSW Chapter 6)

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