Web Ontology Language (OWL)

Michael Eckert 1CS590SW: Web Ontology Language (OWL)

Web Ontology Language(OWL)

CS590SW: Semantic Web (Winter Quarter 2003)

Presentation: Michael Eckert


What is OWL?“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

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.”


Three OWL languages: 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)

W3C’s Architecture for a Semantic Web

XML + NS + xmlschema

Unicode URI

RDF + rdfschema

Web Ontology Language (OWL)


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

Foundation: Description Logics

ClassicDB-Systems

First OrderLogic

DescriptionLogics


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 datatypesobject properties: binary relation between elements of two classes

<owl:ObjectProperty rdf:ID=“producedIn” />


OWL: Complex ClassesForm Classes using class expressions.

Set Operators intersectionOf, unionOf, complementOf

Enumerated Classes: oneOfDefine a class via enumeration of its members closes class extension

Disjoint Classes: disjointWithSet of mutually disjoint classes: one disjointWith assertion per pair


OWL: Property CharacteristicsAre 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 RestrictionsAre 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


OWL: Reuse of OntologiesOWL 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


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 DatamanagementTKDE 7(5):671-682 (1995).

Documents

Web Ontology Language (OWL)