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Web Ontology Language (OWL)

Web Ontology Language (OWL). CS590SW: Semantic Web (Winter Quarter 2003) Presentation: Michael Eckert. What is OWL?. Motivation:.

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Web Ontology Language (OWL)

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  1. Web Ontology Language(OWL) CS590SW: Semantic Web(Winter Quarter 2003)Presentation: Michael Eckert

  2. What is OWL? Motivation: “Computational Agents require machine-readable descriptions of the content and capabilities of web accessible resources. These descriptions must be in addition to the human-readable versions of the information.” “Ontologies facilitate greater machine readability of web content than XML, RDF, and RDF-S by providing additional vocabulary for term descriptions.” “The Web Ontology Language (OWL) is intended to provide a language that can be used to describe the classes and relations between them that are inherent in Web documents and applications” OWL can be used to Formalize a domain by defining classes and properties of those classes Define individuals and assert properties about them Reason about these classes and individuals to the degree permitted by the formal semantics of the OWL language

  3. Three OWL languages: W3C’s Architecture for a Semantic Web Web Ontology Language (OWL) RDF + rdfschema XML + NS + xmlschema Unicode URI • OWL Lite: simplified language primarily for classification hierarchies and simple constraints OWL DL: power corresponds to expressiveness of Descriptions Logics OWL Full: a class can be treated simultaneously as a collection of individuals (extension) and as an individual in its own right (intension)

  4. Foundation: Description Logics Description Logics First Order Logic ClassicDB-Systems  Restriction of the expressiveness of First Order Logic (usually to the degree of PSPACE-completeness) Semantic: set-theoretic interpretation Concepts (Sets), Roles (binary Relations), Individuals (Elements) Various Operators and Quantifiers T(erminological)-Box: definitions and axioms A(ssertional)-Box: information about individuals Note: names of individuals can be used in a T-Box e.g. open world assumption, no unique naming assumtion

  5. OWL: Basic Definitions Defining classes: Class <owl:Class rdf:ID=“Region” /> <owl:Class rdf:ID=“PotableLiquid” /> Building class hierarchies: subClassOf <owl:Class rdf:ID=“Wine”> <rdfs:subClassOf rdf:resource=“#PotableLiquid”> </owl:Class> Defining Individuals: <Region rdf:ID=“CentralCoastRegion”> Simple Properties: datatype properties: binary relation between elements of classes and XML datatypes object properties: binary relation between elements of two classes <owl:ObjectProperty rdf:ID=“producedIn” />

  6. OWL: Complex Classes Form Classes using class expressions.  Set Operators intersectionOf, unionOf, complementOf Enumerated Classes: oneOfDefine a class via enumeration of its members closes class extension  Disjoint Classes: disjointWith Set of mutually disjoint classes: one disjointWith assertion per pair

  7. OWL: Property Characteristics Are given in the property definition and apply globally to all instances of the property. Their specification provides a powerful mechanism for enhanced reasoning about a property.  Specification of domain and range subPropertyOf TransitiveProperty, SymmetricProperty FunctionalProperty, InverseFunctionalProperty (“unique key”) inverseOf OWL: Property Restrictions Are given in a class definition and apply only locally to their containg class.  Quantifiers: allValuesFrom, someValuesFrom Cardinality:cardinality, minCardinality, maxCardinality Relate individuals as particular property values to class: hasValue

  8. OWL: Reuse of Ontologies OWL supports RDF’s namespace mechanism and allows to importing other ontologies into the current knowledgebase via imports.To support effective sharing and reuse of ontologies we additionally need ways to identify correspondences between two ore more ontologies:  Equivalency: sameClassAs, samePropertyAs Identity - Dealing with the no unique naming assumption:sameIndividualAs, differentIndividualFrom

  9. Summary  OWL builds upon XML and RDS  Three increasingly complex languages: OWL Lite, OWL DL, OWL Full  Theoretical foundation: Description Logics  Classes, Properties, Individuals  Reasoning: Property Characteristics, Restrictions, Complex classes  Reuse of Ontologies: Ontology Mapping Literature  W3C Sematic Web: http://www.w3.org/2001/sw/ Web Ontology Language (OWL) Guide Version 1.0http://www.w3.org/TR/owl-guide/ Alexander Borgida: Description Logics in Datamanagement TKDE 7(5):671-682 (1995).

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