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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

Web Ontology Language(OWL)

CS590SW: Semantic Web(Winter Quarter 2003)Presentation: Michael Eckert

what is owl
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

three owl languages
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)
slide4

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

slide5

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” />

slide6

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

slide7

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

slide8

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

slide9

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).