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W3C Recommendation 10 February 2004
This version:
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" http://www.w3.org/TR/2004/REC-owl-ref-20040210/
Latest version:
HYPERLINK "http://www.w3.org/TR/owl-ref/" http://www.w3.org/TR/owl-ref/
Previous version:
HYPERLINK "http://www.w3.org/TR/2003/PR-owl-ref-20031215/" http://www.w3.org/TR/2003/PR-owl-ref-20031215/
Editors:
HYPERLINK "http://www.daml.org/people/mdean/" Mike Dean, BBN Technologies HYPERLINK "http://www.cs.vu.nl/~guus/" Guus Schreiber, Free University Amsterdam
Authors:
HYPERLINK "http://www.cs.man.ac.uk/~seanb/" Sean Bechhofer, University of Manchester HYPERLINK "http://www.cs.vu.nl/~frankh/" Frank van Harmelen, Free University Amsterdam HYPERLINK "http://www.cs.umd.edu/users/hendler/" Jim Hendler, University of Maryland HYPERLINK "http://www.cs.man.ac.uk/~horrocks/" Ian Horrocks, University of Manchester HYPERLINK "http://www.ksl.stanford.edu/people/dlm/" Deborah L. McGuinness, Stanford University HYPERLINK "http://www.bell-labs.com/user/pfps/" Peter F. Patel-Schneider, Bell Labs Research, Lucent Technologies HYPERLINK "http://faculty.olin.edu/~las/" Lynn Andrea Stein, Franklin W. Olin College of Engineering
Please refer to the HYPERLINK "http://www.w3.org/2001/sw/WebOnt/errata" \l "owl-ref" errata for this document, which may include some normative corrections.
See also HYPERLINK "http://www.w3.org/2001/sw/RDFCore/translation/owl-ref" translations.
HYPERLINK "http://www.w3.org/Consortium/Legal/ipr-notice" \l "Copyright" Copyright й 2004 HYPERLINK "http://www.w3.org/" W3Cо ( HYPERLINK "http://www.csail.mit.edu/" MIT, HYPERLINK "http://www.ercim.org/" ERCIM, HYPERLINK "http://www.keio.ac.jp/" Keio), All Rights Reserved. W3C HYPERLINK "http://www.w3.org/Consortium/Legal/ipr-notice" \l "Legal_Disclaimer" liability, HYPERLINK "http://www.w3.org/Consortium/Legal/ipr-notice" \l "W3C_Trademarks" trademark, HYPERLINK "http://www.w3.org/Consortium/Legal/copyright-documents" document use and HYPERLINK "http://www.w3.org/Consortium/Legal/copyright-software" software licensing rules apply.
Abstract
The Web Ontology Language OWL is a semantic markup language for publishing and sharing ontologies on the World Wide Web. OWL is developed as a vocabulary extension of RDF (the Resource Description Framework) and is derived from the DAML+OIL Web Ontology Language. This document contains a structured informal description of the full set of OWL language constructs and is meant to serve as a reference for OWL users who want to construct OWL ontologies.
Status of this document
This document has been reviewed by W3C Members and other interested parties, and it has been endorsed by the Director as a HYPERLINK "http://www.w3.org/2003/06/Process-20030618/tr.html" \l "RecsW3C" W3C Recommendation. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This is one of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-features-20040210/" \l "s1.1" six parts of the W3C Recommendation for OWL, the Web Ontology Language. It has been developed by the HYPERLINK "http://www.w3.org/2001/sw/WebOnt/" Web Ontology Working Group as part of the HYPERLINK "http://www.w3.org/2001/sw/" W3C Semantic Web Activity ( HYPERLINK "http://www.w3.org/2001/sw/Activity" Activity Statement, HYPERLINK "http://www.w3.org/2001/sw/WebOnt/charter" Group Charter) for publication on 10 February 2004.
The design of OWL expressed in earlier versions of these documents has been widely reviewed and satisfies the Working Group's HYPERLINK "http://www.w3.org/TR/webont-req/" technical requirements. The Working Group has addressed HYPERLINK "http://lists.w3.org/Archives/Public/public-webont-comments/" all comments received, making changes as necessary. Changes to this document since HYPERLINK "http://www.w3.org/TR/2003/PR-owl-ref-20031215/" the Proposed Recommendation version are detailed in the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "changes-since-PR" change log.
Comments are welcome at HYPERLINK "mailto:public-webont-comments@w3.org" public-webont-comments@w3.org ( HYPERLINK "http://lists.w3.org/Archives/Public/public-webont-comments/" archive) and general discussion of related technology is welcome at HYPERLINK "mailto:www-rdf-logic@w3.org" www-rdf-logic@w3.org ( HYPERLINK "http://lists.w3.org/Archives/Public/www-rdf-logic/" archive).
A list of HYPERLINK "http://www.w3.org/2001/sw/WebOnt/impls" implementations is available.
The W3C maintains a list of HYPERLINK "http://www.w3.org/2001/sw/WebOnt/discl" any patent disclosures related to this work.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the HYPERLINK "http://www.w3.org/TR/" W3C technical reports index at http://www.w3.org/TR/.
Acknowledgments
Parts of this document are derived from the DAML+OIL (March 2001) Reference Description [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-daml" DAML+OIL] which was submitted as part of the HYPERLINK "http://www.w3.org/Submission/2001/12/" DAML+OIL W3C Note . The sponsors of this document and its predecessor documents are gratefully acknowledged.
Jeremy Carroll, Jim Hendler, Brian McBride and Peter Patel-Schneider provided substantive reviews and contributed text to this document. Jeff Heflin contributed the section on deprecation. Jerome Euzenat contributed the example for an enumerated datatype.
This document is the result of extensive discussions within the HYPERLINK "http://www.w3.org/2001/sw/WebOnt/" Web Ontology Working Group as a whole. The participants in this Working Group included: Yasser alSafadi, Jean-Franчois Baget, James Barnette, Sean Bechhofer, Jonathan Borden, Frederik Brysse, Stephen Buswell, Jeremy Carroll, Dan Connolly, Peter Crowther, Jonathan Dale, Jos De Roo, David De Roure, Mike Dean, Larry Eshelman, JщrЇme Euzenat, Tim Finin, Nicholas Gibbins, Sandro Hawke, Patrick Hayes, Jeff Heflin, Ziv Hellman, James Hendler, Bernard Horan, Masahiro Hori, Ian Horrocks, Jane Hunter, Francesco Iannuzzelli, R№diger Klein, Natasha Kravtsova, Ora Lassila, Massimo Marchiori, Deborah McGuinness, Enrico Motta, Leo Obrst, Mehrdad Omidvari, Martin Pike, Marwan Sabbouh, Guus Schreiber, Noboru Shimizu, Michael Sintek, Michael K. Smith, John Stanton, Lynn Andrea Stein, Herman ter Horst, David Trastour, Frank van Harmelen, Bernard Vatant, Raphael Volz, Evan Wallace, Christopher Welty, Charles White, and John Yanosy.
Contents
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "abstract" Abstract
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "status" Status of this document
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "acknowledge" Acknowledgments
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Intro" 1. Introduction
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Purpose" 1.1 Purpose of this document
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Sublanguages" 1.2 OWL Full/DL/Lite
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Syntax" 1.3 OWL syntax
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Semantics" 1.4 OWL and RDF semantics
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Examples" 1.5 A note about the examples
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Privacy" 1.6 Data aggregation and privacy
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "AppendixList" 1.7 Appendices of this document
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLDocument" 2. OWL document
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DocumentContent" 2.1 Content
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "owl-uri-namespace" 2.2 OWL URI vocabulary and namespace
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "MIMEType" 2.3 MIME type
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Class" 3. Classes
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" 3.1 Class descriptions
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedClass" 3.1.1 Enumeration
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Restriction" 3.1.2 Property restriction
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ValueRestriction" 3.1.2.1 Value constraints
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" 3.1.2.1.1 owl:allValuesFrom
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "someValuesFrom-def" 3.1.2.1.2 owl:someValuesFrom
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "hasValue-def" 3.1.2.1.3 owl:hasValue
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "CardinalityRestriction" 3.1.2.2 Cardinality constraints
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "maxCardinality-def" 3.1.2.2.1 owl:maxCardinality
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "minCardinality-def" 3.1.2.2.2 owl:minCardinality
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "cardinality-def" 3.1.2.2.3 owl:cardinality
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Boolean" 3.1.3 Intersection, union and complement
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "intersectionOf-def" 3.1.3.1 owl:intersectionOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" 3.1.3.2 owl:unionOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "complementOf-def" 3.1.3.3 owl:complementOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassAxioms" 3.2 Class axioms
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "subClassOf-def" 3.2.1 rdfs:subClassOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentClass-def" 3.2.2 owl:equivalentClass
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DescriptionAxiom" 3.2.3 Axioms for complete classes without using owl:equivalentClass
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "disjointWith-def" 3.2.4 owl:disjointWith
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Property" 4. Properties
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "RDFSProperty" 4.1 RDF Schema property constructs
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "subPropertyOf-def" 4.1.1 rdfs:subPropertyOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "domain-def" 4.1.2 rdfs:domain
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "range-def" 4.1.3 rdfs:range
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "PropertyRelation" 4.2 Relations to other properties
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentProperty-def" 4.2.1 owl:equivalentProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "inverseOf-def" 4.2.2 owl:inverseOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "PropertyCardinality" 4.3 Global cardinality restrictions on properties
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "FunctionalProperty-def" 4.3.1 owl:FunctionalProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" 4.3.2 owl:InverseFunctionalProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "PropertyLogic" 4.4 Logical characteristics of properties
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "TransitiveProperty-def" 4.4.1 owl:TransitiveProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "SymmetricProperty-def" 4.4.2 owl:SymmetricProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Individual" 5. Individuals
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "IndividualAxiom" 5.1 Class membership and property values
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "IndividualIdentity" 5.2 Individual identity
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" 5.2.1 owl:sameAs
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "differentFrom-def" 5.2.2 owl:differentFrom
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "AllDifferent-def" 5.2.3 owl:AllDifferent
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Datatype" 6. Datatypes
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "rdf-datatype" 6.1 RDF Datatypes
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedDatatype" 6.2 Enumerated datatype using owl:oneOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeSupport" 6.3 Support for datatype reasoning
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Header" 7. Annotations, ontology header, imports and version information
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Annotations" 7.1 Annotations
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Ontology-def" 7.2 Ontology header
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "imports-def" 7.3 Importing ontologies
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "VersionInformation" 7.4 Version information
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "versionInfo-def" 7.4.1 owl:versionInfo
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "priorVersion-def" 7.4.2 owl:priorVersion
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "backwardCompatibleWith-def" 7.4.3 owl:backwardCompatibleWith
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "incompatibleWith-def" 7.4.4 owl:incompatibleWith
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Deprecation" 7.4.5 owl:DeprecatedClass and owl:DeprecatedProperty
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Sublanguage-def" 8. OWL Full, OWL DL and OWL Lite
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLFull" 8.1 OWL Full
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLDL" 8.2 OWL DL
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLLite" 8.3 OWL Lite
Appendix A: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appA" Index of all language elements
Appendix B: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appB" RDF Schema of OWL
Appendix C: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appC" OWL Quick Reference
Appendix D: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appD" Changes from DAML+OIL
Appendix E: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "app-DLinRDF" Rules of Thumb for OWL DL ontologies
Appendix F: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "changes-since-PR" Change Log since PR
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "References" References
1. Introduction
1.1 Purpose of this document
This document gives a systematic, compact and informative description of all the modelling primitives of OWL, using the RDF/XML exchange syntax for OWL. We expect this document to serve as a reference guide for users of the OWL language.
This document is one component of the description of OWL, the Web Ontology Language, being produced by the W3C Web Ontology Working Group. The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-features-20040210/" \l "s1.1" Document Roadmap section of the OWL Overview document describes each of the different parts and how they fit together. Readers unfamiliar with OWL may wish to first consult the OWL Overview document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-OWL-Overview" OWL Overview], and subsequently the OWL Guide [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide] for a more narrative description and examples of the use of the language.
This document assumes the reader is familiar with the basic concepts of RDF [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts] and has a working knowledge of the RDF/XML syntax [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-syntax" RDF/XML Syntax] and of RDF Schema [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-vocabulary" RDF Vocabulary].
The normative reference on the precise syntax of the OWL language constructs can be found in the OWL Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS]. That document also contains a precise definition of the meaning of the language constructs in the form of a model-theoretic semantics. Notions such as consistency of OWL ontologies are discussed in that document.
Use cases and requirements for the OWL language are described in the OWL requirements document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-requirements" OWL Requirements]. Test cases for OWL tools (e.g., entailment tests, consistency tests) are specified in the Test document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-test" OWL Test Cases] .
1.2 OWL Full/DL/Lite
As also discussed in the OWL Overview document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-OWL-Overview" OWL Overview], and subsequently the OWL Guide [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide], the OWL language provides two specific subsets that we believe will be of use to implementors and language users. OWL Lite was designed for easy implementation and to provide users with a functional subset that will get them started in the use of OWL. OWL DL (where DL stands for "Description Logic") was designed to support the existing Description Logic business segment and to provide a language subset that has desirable computational properties for reasoning systems. The complete OWL language (called OWL Full to distinguish it from the subsets) relaxes some of the constraints on OWL DL so as to make available features which may be of use to many database and knowledge representation systems, but which violate the constraints of Description Logic reasoners.
NOTE: RDF documents will generally be in OWL Full, unless they are specifically constructed to be in OWL DL or Lite.
OWL Full and OWL DL support the same set of OWL language constructs. Their difference lies in restrictions on the use of some of those features and on the use of RDF features. OWL Full allows free mixing of OWL with RDF Schema and, like RDF Schema, does not enforce a strict separation of classes, properties, individuals and data values. OWL DL puts constraints on the mixing with RDF and requires disjointness of classes, properties, individuals and data values. The main reason for having the OWL DL sublanguage is that tool builders have developed powerful reasoning systems which support ontologies constrained by the restrictions required for OWL DL. For the formal definitions of the differences between OWL Full and OWL DL the reader is referred to the Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS]. HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLDL" Sec. 8.2 "OWL DL" summarizes the differences between OWL Full and OWL DL.
OWL Lite is a sublanguage of OWL DL that supports only a subset of the OWL language constructs. OWL Lite is particularly targeted at tool builders, who want to support OWL, but want to start with a relatively simple basic set of language features. OWL Lite abides by the same semantic restrictions as OWL DL, allowing reasoning engines to guarantee certain desirable properties. A summary of the language constructs allowed in OWL Lite is given in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLLite" Sec. 8.3. For a more formal description of the subset of OWL language constructs supported by OWL Lite the reader is referred to the Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS].
NOTE: RDF users upgrading to OWL should be aware that OWL Lite is not simply an extension of RDF Schema. OWL Lite is a light version of OWL DL and puts constraints on the use of the RDF vocabulary (e.g., disjointness of classes, properties, etc.). OWL Full is designed for maximal RDF compatibility and is therefore the natural place to start for RDF users. When opting for either OWL DL or OWL Lite one should consider whether the advantages of OWL DL/Lite (e.g., reasoning support) outweigh the DL/Lite restrictions on the use of OWL and RDF constructs.
NOTE: OWL Lite is defined in this document as a number of additional restrictions on OWL DL. This mean that, OWL DL constructs are also part of OWL Lite, unless explicitly stated otherwise. HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLLite" Sec. 8.3.provides a summary of these additional OWL Lite restrictions.
1.3 OWL syntax
An OWL ontology is an RDF graph [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts], which is in turn a set of RDF triples. As with any RDF graph, an OWL ontology graph can be written in many different syntactic forms (as described in the RDF/XML Syntax Specification (Revised) [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-syntax" RDF/XML Syntax]). The current document uses some specific syntactic forms of RDF/XML for representing triples (as does the Guide document) . However, the meaning of an OWL ontology is solely determined by the RDF graph. Thus, it is allowable to use other syntactic RDF/XML forms, as long as these result in the same underlying set of RDF triples. Such other syntactic forms would then carry exactly the same meaning as the syntactic form used in this document.
As a simple example of an alternative syntactic form resulting in the same RDF triples, consider the following RDF/XML syntax:
The following RDF/XML syntax:
encodes the same set of RDF triples, and therefore would convey the same meaning.
1.4 OWL and RDF semantics
OWL is a vocabulary extension of RDF [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-RDF-Semantics" RDF Semantics]. Thus any RDF graph forms an OWL Full ontology. Further, the meaning given to an RDF graph by OWL includes the meaning given to the graph by RDF. OWL Full ontologies can thus include arbitrary RDF content, which is treated in a manner consistent with its treatment by RDF. OWL assigns an additional meaning to certain RDF triples. The OWL Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS] specifies exactly which triples are assigned a specific meaning, and what this meaning is.
NOTE: As remarked before, OWL DL and OWL Lite extend the RDF vocabulary, but also put restrictions on the use of this vocabulary. Therefore, RDF documents will generally be in OWL Full, unless they are specifically constructed to be in OWL DL or Lite.
1.5 A note about the examples
For readability purposes the examples in this document assume the XML entities &rdf;, &rdfs;, &owl; and &xsd; (for XML Schema datatypes) are defined in the same way as in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appB" Appendix B. The same assumption holds for the corresponding namespaces rdf:, rdfs:, owl: and xsd:.
The examples in this document are meant to serve as illustrations of the use of OWL language constructs. They do not form one consistent ontology. For an extended example the reader is referred to the Guide document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide].
1.6 Data Aggregation and Privacy
OWL's ability to express ontological information about individuals appearing in multiple documents supports linking of data from diverse sources in a principled way. The underlying semantics provides support for inferences over this data that may yield unexpected results. In particular, the ability to express equivalences using HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" owl:sameAs can be used to state that seemingly different individuals are actually the same. Similarly, HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" owl:InverseFunctionalProperty can be used to link individuals together. For example, if a property such as SocialSecurityNumber is an owl:InverseFunctionalProperty, then two separate individuals could be inferred to be identical based on having the same value of that property. When individuals are determined to be the same by such means, information about them from different sources can be merged. This aggregation can be used to determine facts that are not directly represented in any one source.
The ability of the Semantic Web to link information from multiple sources is a desirable and powerful feature that can be used in many applications. However, the capability to merge data from multiple sources, combined with the inferential power of OWL, does have potential for abuse. It may even be illegal to create or to process such linked information in countries with data protection laws, especially in the EU, without having a valid legal reason for such processing. Therefore, great care should be taken when using OWL with any kind of personal data that might be linked with other data sources or ontologies. Detailed security solutions were considered out of scope for the Working Group. Work currently underway elsewhere is expected to address these issues with a variety of security and preference solutions -- see for example HYPERLINK "http://www.oasis-open.org/committees/security/charter.php" SAML and HYPERLINK "http://www.w3.org/P3P/" P3P
1.7 Appendices to this document
This document has a set of appendices containing additional information.
Links in this document that are attached to definitions of language constructs provide access to the OWL Semantics and Abstract Syntax [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS]. HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appA" Appendix A contains a systematic set of links for each language construct to the corresponding sections in the Guide and the S&AS documents.
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appB" Appendix B contains a RDF schema for the OWL language constructs. This schema provides information about the OWL vocabulary that could be a useful reference point for ontology builders and tool developers. The restrictions provided by the schema on the OWL classes and properties are informative and not complete. Also, this schema does not make distinctions between OWL Full, OWL DL and OWL Lite. Conventionally, classes have a leading uppercase character; properties a leading lowercase character. Thus, owl:Ontology is a class, and owl:imports is a property.
NOTE: The RDF Schema file for OWL is not expected to be imported explicitly (i.e., with owl:imports) into an ontology. The schema has an informative status and is meant to provide the classes and properties to be used in the RDF/XML syntax. People that do import this schema should expect the resulting ontology to be an OWL Full ontology.
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appC" Appendix C gives a tabular overview of the OWL vocabulary in terms of the built-in OWL classes and properties (the latter with their domain and range).
For readers familiar with DAML+OIL, HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appD" Appendix D lists many of the changes between DAML+OIL and OWL.
Finally, HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "app-DLinRDF" Appendix E provides a set of practical guidelines for specifying OWL DL ontologies in RDF.
2. OWL document
Information in OWL is gathered into ontologies, which can then be stored as documents in the World Wide Web. One aspect of OWL, the importing of ontologies, depends on this ability to store OWL ontologies in the Web.
2.1 Content
An OWL document consists of optional HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Header" ontology headers (generally at most one) plus any number of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Class" class axioms, HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Property" property axioms, and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Individual" facts about individuals. Please note that "axiom" is the formal term used in the S&AS document. These axioms are somewhat more informally called "definitions" in the Guide and Overview documents.
NOTE: OWL does not impose any order on OWL components. Humans writing ontologies are likely to use some sort of ordering, for example putting the ontology header in the beginning, but this has no impact on the meaning. Tools should not assume any order.
As with most RDF documents, the OWL code should be subelements of a rdf:RDF element. This enclosing element generally holds XML namespace and base declarations. Also, an OWL ontology document often starts with several entity declarations. For a typical example of this sort of information, see the example wine and food ontologies discussed in the Guide document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide].
2.2 OWL built-in vocabulary
The built-in vocabulary for OWL all comes from the OWL namespace
http://www.w3.org/2002/07/owl#
conventionally associated with the namespace name owl. It is recommended that ontologies not use names from this namespace except for the built-in vocabulary. OWL tool builders should feel free to signal a warning if other names from this namespace are used, but should otherwise continue as normal.
2.3 MIME type
The Web Ontology Working Group has not requested a separate MIME type for OWL documents. Instead, we recommend to use the MIME type requested by the RDF Core Working Group, namely application/rdf+xml [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts], or alternatively the XML MIME type application/xml.
As file extension, we recommend to use either .rdf or .owl.
3. Classes
Classes provide an abstraction mechanism for grouping resources with similar characteristics. Like RDF classes, every OWL class is associated with a set of individuals, called the class extension. The individuals in the class extension are called the instances of the class. A class has an intensional meaning (the underlying concept) which is related but not equal to its class extension. Thus, two classes may have the same class extension, but still be different classes.
When in this document we use wording such as "a class of individuals ..", this should be read as "a class with a class extension containing individuals ...".
NOTE: In OWL Lite and OWL DL an individual can never be at the same time a class: classes and individuals form disjoint domains (as do properties and data values). OWL Full allows the freedom of RDF Schema: a class may act as an instance of another (meta)class.
OWL classes are described through "class descriptions", which can be combined into "class axioms". We first describe class descriptions and subsequently turn to class axioms.
3.1 Class descriptions
A class description is the term used in this document (and in the OWL Semantics and Abstract Syntax) for the basic building blocks of class axioms (informally called class definitions in the Overview and Guide documents). A class description describes an OWL class, either by a class name or by specifying the class extension of an unnamed anonymous class.
OWL distinguishes six types of class descriptions:
a class identifier (a URI reference)
an exhaustive HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedClass" enumeration of individuals that together form the instances of a class
a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Restriction" property restriction
the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "intersectionOf-def" intersection of two or more class descriptions
the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" union of two or more class descriptions
the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "complementOf-def" complement of a class description
The first type is special in the sense that it describes a class through a class name (syntactically represented as a URI reference). The other five types of class descriptions describe an anonymous class by placing constraints on the class extension.
Class descriptions of type 2-6 describe, respectively, a class that contains exactly the enumerated individuals (2nd type), a class of all individuals which satisfy a particular property restriction (3rd type), or a class that satisfies boolean combinations of class descriptions (4th, 5th and 6th type). Intersection, union and complement can be respectively seen as the logical AND, OR and NOT operators. The four latter types of class descriptions lead to nested class descriptions and can thus in theory lead to arbitrarily complex class descriptions. In practice, the level of nesting is usually limited.
A type 1 class description is syntactically represented as an named instance of owl:Class, a subclass of rdfs:Class:
This will assert the triple "ex:Human rdf:type owl:Class .", where ex: is the namespace of the relevant ontology .
NOTE: In OWL Lite and OWL DL, owl:Class (or owl:Restriction, see further) must be used for all class descriptions.
NOTE: owl:Class is defined as a subclass of rdfs:Class. The rationale for having a separate OWL class construct lies in the restrictions on OWL DL (and thus also on OWL Lite), which imply that not all RDFS classes are legal OWL DL classes. In OWL Full these restrictions do not exist and therefore owl:Class and rdfs:Class are equivalent in OWL Full.
The other five forms of class descriptions consist of a set of RDF triples in which a blank node represents the class being described. That blank node has an rdf:type property whose value is owl:Class.
NOTE: If one provides an RDF identifier for class descriptions of the enumeration, intersection, union or complement type, this is not considered to be a class description, but a special kind of class axiom for complete classes. See HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DescriptionAxiom" Sec. 3.2.3 for details.
NOTE: In this document we sometimes use for readability purposes the shorthand "class description" to refer to "the class being described by the class description". Strictly speaking, these are different in the case of class descriptions of type 2-6: the class is represented by the corresponding blank node; the class description is represented by the triples that have this blank node as their subject.
Two OWL class identifiers are predefined, namely the classes HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Thing" owl:Thing and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Nothing" owl:Nothing. The class extension of owl:Thing is the set of all individuals. The class extension of owl:Nothing is the empty set. Consequently, every OWL class is a subclass of owl:Thing and owl:Nothing is a subclass of every class (for the meaning of the subclass relation, see the section on HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "subClassOf-def" rdfs:subClassOf).
3.1.1 Enumeration
A class description of the "enumeration" kind is defined with the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_oneOf" owl:oneOf property. The value of this built-in OWL property must be a list of individuals that are the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Individual" instances of the class. This enables a class to be described by exhaustively enumerating its instances. The class extension of a class described with owl:oneOf contains exactly the enumerated individuals, no more, no less. The list of individuals is typically represented with the help of the RDF construct rdf:parseType="Collection", which provides a convenient shorthand for writing down a set of list elements. For example, the following RDF/XML syntax defines a class of all continents:
The RDF/XML syntax refers to some individual (remember: all individuals are by definition instances of owl:Thing).
In the section on datatypes we will see another use of the owl:oneOf construct, namely to define an HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedDatatype" enumeration of data values.
NOTE: Enumeration is not part of OWL Lite
3.1.2 Property restrictions
A property restriction is a special kind of class description. It describes an anonymous class, namely a class of all individuals that satisfy the restriction. OWL distinguishes two kinds of property restrictions: value constraints and cardinality constraints.
A HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ValueRestriction" value constraint puts constraints on the range of the property when applied to this particular class description. For example, we might want to refer to those individuals whose value of the property adjacentTo should be some Region, and then use this within a class axiom, perhaps even a class axiom for Region itself. Note that this is different from rdfs:range, which is applied to all situations in which the property is used.
A HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "CardinalityRestriction" cardinality constraint puts constraints on the number of values a property can take, in the context of this particular class description. For example, we might want to say that for a soccer team the hasPlayer property has 11 values. For a basketball team the same property would have only 5 values.
OWL also supports a limited set of constructs for defining global property cardinality, namely HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "FunctionalProperty-def" owl:FunctionalProperty and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" owl:InverseFunctionalProperty (see the section on properties).
Property restrictions have the following general form:
(precisely one value or cardinality constraint, see below)
The class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Restriction" owl:Restriction is defined as a subclass of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Class-def" owl:Class. A restriction class should have exactly one triple linking the restriction to a particular property, using the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_onProperty" owl:onProperty property. The restriction class should also have exactly one triple that represents the value constraint c.q. cardinality constraint on the property under consideration, e.g., that the cardinality of the property is exactly 1.
Property restrictions can be applied both to HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeProperty-def" datatype properties (properties for which the value is a data literal) and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ObjectProperty-def" object properties (properties for which the value is an individual). For more information about this distinction, see the section on HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Property" properties.
3.1.2.1 Value constraints
3.1.2.1.1 owl:allValuesFrom
The value constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_allValuesFrom" owl:allValuesFrom is a built-in OWL property that links a restriction class to either a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class description or a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DataRange" data range. A restriction containing an owl:allValuesFrom constraint is used to describe a class of all individuals for which all values of the property under consideration are either members of the class extension of the class description or are data values within the specified data range. In other words, it defines a class of individuals x for which holds that if the pair (x,y) is an instance of P (the property concerned), then y should be an instance of the class description or a value in the data range, respectively.
A simple example:
This example describes an anonymous OWL class of all individuals for which the hasParent property only has values of class Human. Note that this class description does not state that the property always has values of this class; just that this is true for individuals that belong to the class extension of the anonymous restriction class.
NOTE: In OWL Lite the only type of class description allowed as object of owl:allValuesFrom is a class name.
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom constraint is analogous to the universal (for-all) quantifier of Predicate logic - for each instance of the class that is being described, every value for P must fulfill the constraint. Also notice that the correspondence of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom with the universal quantifier means that an HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom constraint for a property P is trivially satisfied for an individual that has no value for property P at all. To see why this is so, observe that the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom constraint demands that all values of P should be of type T, and if no such values exist, the constraint is trivially true.
3.1.2.1.2 owl:someValuesFrom
The value constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_someValuesFrom" owl:someValuesFrom is a built-in OWL property that links a restriction class to a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class description or a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DataRange" data range. A restriction containing an owl:someValuesFrom constraint describes a class of all individuals for which at least one value of the property concerned is an instance of the class description or a data value in the data range. In other words, it defines a class of individuals x for which there is at least one y (either an instance of the class description or value of the data range) such that the pair (x,y) is an instance of P. This does not exclude that there are other instances (x,y') of P for which y' does not belong to the class description or data range.
The following example defines a class of individuals which have at least one parent who is a physician:
The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "someValuesFrom-def" owl:someValuesFrom constraint is analogous to the existential quantifier of Predicate logic - for each instance of the class that is being defined, there exists at least one value for P that fulfills the constraint.
NOTE: In OWL Lite the only type of class description allowed as object of owl:someValuesFrom is a class name.
3.1.2.1.3 owl:hasValue
The value constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_hasValue" owl:hasValue is a built-in OWL property that links a restriction class to a value V, which can be either an HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Individual" individual or a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Datatype" data value. A restriction containing a owl:hasValue constraint describes a class of all individuals for which the property concerned has at least one value semantically equal to V (it may have other values as well).
NOTE: for datatypes "semantically equal" means that the lexical representation of the literals maps to the same value. For individuals it means that they either have the same URI reference or are defined as being the same individual (see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" owl:sameAs).
NOTE: the value constraint owl:hasValue is not included in OWL Lite.
The following example describes the class of individuals who have the individual referred to as Clinton as their parent:
3.1.2.2 Cardinality constraints
In OWL, like in RDF, it is assumed that any instance of a class may have an arbitrary number (zero or more) of values for a particular property. To make a property required (at least one), to allow only a specific number of values for that property, or to insist that a property must not occur, cardinality constraints can be used. OWL provides three constructs for restricting the cardinality of properties locally within a class context.
NOTE: OWL Lite includes the use of all three types of cardinality constraints, but only when used with the values "0" or "1".
3.1.2.2.1 owl:maxCardinality
The cardinality constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_maxCardinality" owl:maxCardinality is a built-in OWL property that links a restriction class to a data value belonging to the value space of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:maxCardinality constraint describes a class of all individuals that have at most N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
The following example describes a class of individuals that have at most two parents:
2
RDF datatyping is discussed in more detail in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Datatype" Sec. 6.
3.1.2.2.2 owl:minCardinality
The cardinality constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_minCardinality" owl:minCardinality is a built-in OWL property that links a restriction class to a data value belonging to the value space of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:minCardinality constraint describes a class of all individuals that have at least N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
The following example describes a class of individuals that have at least two parents:
2
Note that an owl:minCardinality of one or more means that all instances of the class must have a value for the property.
3.1.2.2.3 owl:cardinality
The cardinality constraint HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_cardinality" owl:cardinality is a built-in OWL property that links a restriction class to a data value belonging to the range of the XML Schema datatype nonNegativeInteger. A restriction containing an owl:cardinality constraint describes a class of all individuals that have exactly N semantically distinct values (individuals or data values) for the property concerned, where N is the value of the cardinality constraint. Syntactically, the cardinality constraint is represented as an RDF property element with the corresponding rdf:datatype attribute.
This construct is in fact redundant as it can always be replaced by a pair of matching HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "minCardinality-def" owl:minCardinality and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "maxCardinality-def" owl:maxCardinality constraints with the same value. It is included as a convenient shorthand for the user.
The following example describes a class of individuals that have exactly two parents:
2
3.1.3 Intersection, union and complement
The three types of class descriptions in this section represent the more advanced class constructors that are used in Description Logic. They can be viewed as representing the AND, OR and NOT operators on classes. The three operators get the standard set-operator names: intersection, union and complement. These language constructs also share the characteristic that they contain nested class descriptions, either one (complement) or more (union, intersection).
3.1.3.1 owl:intersectionOf
The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_intersectionOf" owl:intersectionOf property links a class to a list of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class descriptions. An owl:intersectionOf statement describes a class for which the class extension contains precisely those individuals that are members of the class extension of all class descriptions in the list.
An example:
In this example the value of owl:intersectionOf is a list of two class descriptions, namely two enumerations, both describing a class with two individuals. The resulting intersection is a class with one individual, namely Tosca. as this is the only individual that is common to both enumerations.
NOTE: This assumes that the three individuals are all different. In fact, this is not by definition true in OWL. Different URI references may refer to the same individuals, because OWL does not have a "unique names" assumption. In HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Individual" Sec. 5 one can find OWL language constructs for making constraints about equality and difference of individuals.
NOTE: In this example we use enumerations to make clear what the meaning is of this language construct. See the OWL Guide [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide] for more typical examples.
NOTE: OWL Lite is restricted in its use of owl:intersectionOf. This is discussed later in this document, see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DescriptionAxiom" Sec. 3.2.3
owl:intersectionOf can be viewed as being analogous to logical conjunction.
3.1.3.2 owl:unionOf
The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_unionOf" owl:unionOf property links a class to a list of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class descriptions. An owl:unionOf statement describes an anonymous class for which the class extension contains those individuals that occur in at least one of the class extensions of the class descriptions in the list.
An example:
This class description describes a class for which the class extension contains three individuals, namely Tosca, Salome, and Turandot (assuming they are all different).
NOTE: owl:unionOf is not part of OWL Lite.
owl:unionOf is analogous to logical disjunction.
3.1.3.3 owl:complementOf
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_complementOf" owl:complementOf property links a class to precisely one HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class description. An owl:complementOf statement describes a class for which the class extension contains exactly those individuals that do not belong to the class extension of the class description that is the object of the statement. owl:complementOf is analogous to logical negation: the class extension consists of those individuals that are NOT members of the class extension of the complement class.
As an example of the use of complement, the expression "not meat" could be written as:
The extension of this class description contains all individuals that do not belong to the class Meat.
NOTE: owl:complementOf is not part of OWL Lite.
3.2 Class axioms
Class descriptions form the building blocks for defining classes through class axioms. The simplest form of a class axiom is a class description of type 1, It just states the existence of a class, using owl:Class with a class identifier.
For example, the following class axiom declares the URI reference #Human to be the name of an OWL class:
This is correct OWL, but does not tell us very much about the class Human. Class axioms typically contain additional components that state necessary and/or sufficient characteristics of a class. OWL contains three language constructs for combining class descriptions into class axioms:
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "subClassOf-def" rdfs:subClassOf allows one to say that the class extension of a class description is a subset of the class extension of another class description.
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentClass-def" owl:equivalentClass allows one to say that a class description has exactly the same class extension as another class description.
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "disjointWith-def" owl:disjointWith allows one to say that the class extension of a class description has no members in common with the class extension of another class description.
Syntactically, these three language constructs are properties that have a class description as both domain and range. We discuss these properties in more detail in the following subsections.
In addition, OWL allows class axioms in which a class description of the enumeration or the set-operator type is given a name. These class axioms are semantically equivalent to class axioms with a owl:equivalentClass statement, so these will be discussed right after that subsection (see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DescriptionAxiom" Sec. 3.2.3 "Axioms for complete classes without using owl:equivalentClass").
3.2.1 rdfs:subClassOf
AXIOM SCHEMA: class description rdfs:subClassOf class description
The rdfs:subClassOf construct is defined as part of RDF Schema [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-vocabulary" RDF Vocabulary]. Its meaning in OWL is exactly the same: if the class description C1 is defined as a subclass of class description C2, then the set of individuals in the class extension of C1 should be a subset of the set of individuals in the class extension of C2. A class is by definition a subclass of itself (as the subset may be the complete set).
An example:
This class axiom declares a subclass relation between two OWL classes that are described through their names (Opera and MusicalWork). Subclass relations provide necessary conditions for belonging to a class. In this case, to be an opera the individual also needs to be a musical work.
NOTE: In OWL Lite the subject of an rdfs:subClassOf statement must be a class identifier. The object must be either a class identifier or a property restriction.
For any class there may be any number of subClassOf axioms. For example, we could add the following axiom about the class Opera:
1
This class axiom contains a property restriction. The example states that Opera is a subclass of an anonymous OWL class (remember: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Restriction-def" owl:Restriction is a subclass of owl:Class) that has as its class extension the set of all individuals for which the property hasLibrettist has at least one value. Thus, operas should have at least one librettist.
Class axioms can get more complex when class descriptions are nested. For example, property restrictions with an HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom or HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "someValuesFrom-def" owl:someValuesFrom statement may point to any class description. Consider the following example:
This example shows the use of the owl:oneOf construct. The class axiom defines traditional Italian opera as a subclass of a class of operas that have as opera type either opera seria or opera buffa (without an additional cardinality constraint, it could actually have both values).
More examples can be found in the Guide document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide]. Subclass axioms provide us with partial definitions: they represent necessary but not sufficient conditions for establishing class membership of an individual. In the next subsection we will see that for defining necessary and sufficient conditions OWL provides the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentClass-def" owl:equivalentClass construct. As a stepping stone to such axioms, consider the following example:
1
This class axiom states that an operetta is a musical work, that has a at least one librettist and is not an opera. The use of the subclass relation leaves open the possibility that there are other musical works that have a librettist and are not operas. If we had wanted to say that operetta's are exactly those musical works that have a librettist but are not operas, we would need to use the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentClass-def" owl:equivalentClass construct.
3.2.2 owl:equivalentClass
AXIOM SCHEMA: class description owl:equivalentClass class description
A class axiom may contain (multiple) HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_equivalentClass" owl:equivalentClass statements. owl:equivalentClass is a built-in property that links a class description to another class description. The meaning of such a class axiom is that the two class descriptions involved have the same class extension (i.e., both class extensions contain exactly the same set of individuals).
In its simplest form, an equivalentClass axiom states the equivalence (in terms of their class extension) of two named classes. An example:
NOTE: The use of owl:equivalentClass does not imply class equality. Class equality means that the classes have the same intensional meaning (denote the same concept). In the example above, the concept of "President of the US" is related to, but not equal to the concept of the principal resident of a certain estate. Real class equality can only be expressed with the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" owl:sameAs construct. As this requires treating classes as individuals, class equality can only be expressed in OWL Full.
Axioms with owl:equivalentClass can also be used to define an enumerated class by linking a type 1 class description (a class identifier) to a type 2 class description (an enumeration). An example:
This class axiom defines the class of operas that together represent the "Da Ponte operas of Mozart" (a popular subject in musicology). By using the equivalentClass construct we can state necessary and sufficient conditions for class membership, in this case consisting of an enumeration of three individuals, no less, no more.
NOTE: OWL DL does not put any constraints on the types of class descriptions that can be used as subject and object of an owl:equivalentClass statement. In OWL Lite the subject must be a class name and the object must be either a class name or a property restriction.
NOTE: Although in principle different types of class descriptions are allowed as the subject of an equivalentClass statement, in practice it usually is some class identifier. This is also true for the examples in this section.
It is possible to have multiple equivalentClass axioms about the same class. However, this requires care. Both axioms must lead to the same outcome, i.e. exactly the same class extension. For example, an alternate equivalentClass axiom for Mozart's "Da Ponte operas" could be the following one:
This states that the class extension of the Da Ponte operas of Mozart corresponds exactly to those operas which are composed by Mozart and for which the libretto is written by Da Ponte (note: intersection = "and"). This axiom indeed defines a class with exactly the same instances as the previous axiom.
NOTE: If we wanted to "upgrade" an axiom of the form "A subClassOf B" to "A equivalentClass B" (meaning that the class extension of A is not just any subset, but in fact the same set as the class extension of B), we could add a second subClassOf axiom of the form (B subClassOf A), which by definition makes the two class extensions equivalent (and thus has the same meaning as "A equivalentClass B"). Such subClassOf "cycles" are explicitly allowed. As OWL is usable in a distributed environment, this can be a useful feature.
3.2.3 Axioms for complete classes without using owl:equivalentClass
AXIOM SCHEMA: named class description of type 2 (with owl:oneOf) or type 4-6 (with owl:intersectionOf, owl:unionOf or owl:complementOf
OWL allows users to define class axioms by giving a name to class descriptions of the enumeration or set-operator type. Such a class axiom defines necessary and sufficient conditions for establishing class membership. An example:
This class axiom should be interpreted as follows: the class extension of the class DaPonteOperaOfMozart is exactly defined by the enumeration.
This class axiom is semantically equivalent to the first opera example in the previous section, which included an additional owl:equivalentClass statement. Axioms of this type can also be constructed with owl:intersectionOf, owl:unionOf and owl:complementOf. An example with a union could be:
This class axiom states that the class extension of LivingBeing exactly corresponds to the union of the class extensions of Plant and Animal.
NOTE: OWL Lite only includes class axioms of this type which are constructed with the owl:intersectionOf property. The values of the intersectionOf list must be class identifiers and/or property restrictions. Thus, "complete class" axioms using enumeration, complement and union are not allowed in OWL Lite.
3.2.4 owl:disjointWith
AXIOM SCHEMA: class description owl:disjointWith class description
A class axiom may also contain (multiple) HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_disjointWith" owl:disjointWith statements. owl:disjointWith is a built-in OWL property with a class description as domain and range. Each owl:disjointWith statement asserts that the class extensions of the two class descriptions involved have no individuals in common. Like axioms with rdfs:subClassOf, declaring two classes to be disjoint is a partial definition: it imposes a necessary but not sufficient condition on the class.
This is a popular example of class disjointness:
Whether this is actually true is a matter for biologists to decide. The following example shows a common use of class disjointness in subclass hierarchies:
Here, owl:disjointWith statements are used together with HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" owl:unionOf in order to define a set of mutually disjoint and complete subclasses of a superclass. In natural language: every MusicDrama is either an opera, an Operetta, or a Musical (the subclass partitioning is complete) and individuals belonging to one subclass, e.g., Opera, cannot belong to another subclass, e.g., Musical (disjoint or non-overlapping subclasses). This is a common modelling notion used in many data-modelling notations.
NOTE: OWL Lite does not allow the use of owl:disjointWith.
4. Properties
OWL distinguishes between two main categories of properties that an ontology builder may want to define:
Object properties link individuals to individuals.
Datatype properties link individuals to data values.
NOTE: OWL also has the notion of annotation properties (owl:AnnotationProperty) and ontology properties (owl:OntologyProperty). These are needed in OWL DL for semantic reasons. See HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Header" Sec. 7 and the OWL Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS].
An object property is defined as an instance of the built-in OWL class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_ObjectProperty" owl:ObjectProperty. A datatype property is defined as an instance of the built-in OWL class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DatatypeProperty" owl:DatatypeProperty. Both owl:ObjectProperty and owl:DatatypeProperty are subclasses of the RDF class rdf:Property (see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "appB" Appendix B).
NOTE: In OWL Full, object properties and datatype properties are not disjoint. Because data values can be treated as individuals, datatype properties are effectively subclasses of object properties. In OWL Full owl:ObjectProperty is equivalent to rdf:Property In practice, this mainly has consequences for the use of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" owl:InverseFunctionalProperty. See also the OWL Full characterization in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLFull" Sec. 8.1.
A property axiom defines characteristics of a property. In its simplest form, a property axiom just defines the existence of a property. For example:
This defines a property with the restriction that its values should be individuals.
Often, property axioms define additional characteristics of properties. OWL supports the following constructs for property axioms:
RDF Schema constructs: rdfs:subPropertyOf, rdfs:domain and rdfs:range
relations to other properties: owl:equivalentProperty and owl:inverseOf
global cardinality constraints: owl:FunctionalProperty and owl:InverseFunctionalProperty
logical property characteristics: owl:SymmetricProperty and owl:TransitiveProperty
In the next subsections, the various types of property axioms are discussed in more detail.
NOTE: In this section we use the term "property extension" in a similar fashion to "class extension". The property extension is the set of instances that is associated with the property. Instances of properties are not single elements, but subject-object pairs of property statements. In relational database terms, property instances would be called "tuples" of a binary relation (the property).
4.1 RDF Schema constructs
The constructs in this section are discussed in detail in the RDF Schema document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-vocabulary" RDF Vocabulary]. The description in this section provides a synopsis of these constructs and provides some OWL-specific aspects and examples.
4.1.1 rdfs:subPropertyOf
A rdfs:subPropertyOf axiom defines that the property is a subproperty of some other property. Formally this means that if P1 is a subproperty of P2, then the property extension of P1 (a set of pairs) should be a subset of the property extension of P2 (also a set of pairs).
An example:
This states that all instances (pairs) contained in the property extension of the property "hasMother" are also members of the property extension of the property "hasParent".
Subproperty axioms can be applied to both datatype properties and object properties.
NOTE: In OWL DL the subject and object of a subproperty statement must be either both datatype properties or both object properties.
4.1.2 rdfs:domain
For a property one can define (multiple) rdfs:domain axioms. Syntactically, rdfs:domain is a built-in property that links a property (some instance of the class rdf:Property) to a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class description. An rdfs:domain axiom asserts that the subjects of such property statements must belong to the class extension of the indicated class description.
Multiple rdfs:domain axioms are allowed and should be interpreted as a conjunction: these restrict the domain of the property to those individuals that belong to the intersection of the class descriptions. If one would want to say that multiple classes can act as domain, one should use a class description of the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" owl:unionOf form. For example, if we want to say that the domain of the property hasBankAccount can be either a Person or a Corporation, we would need to say something like this:
NOTE: In OWL Lite the value of rdfs:domain must be a class identifier.
4.1.3 rdfs:range
For a property one can define (multiple) rdfs:range axioms. Syntactically, rdfs:range is a built-in property that links a property (some instance of the class rdf:Property) to to either a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ClassDescription" class description or a HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DataRange" data range. An rdfs:range axiom asserts that the values of this property must belong to the class extension of the class description or to data values in the specified data range.
Multiple range restrictions are interpreted as stating that the range of the property is the intersection of all ranges (i.e., the intersection of the class extension of the class descriptions c.q. the intersection of the data ranges). Similar to HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "domain-def" rdfs:domain, multiple alternative ranges can be specified by using a class description of the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" owl:unionOf form (see the previous subsection).
Note that, unlike any of the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ValueRestriction" value constraints described in the section on class descriptions, rdfs:range restrictions are global. Value constraints such as HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom are used in a class description and are only enforced on the property when applied to that class. In contrast, rdfs:range restrictions apply to the property irrespective of the class to which it is applied. Thus, rdfs:range should be used with care.
NOTE: In OWL Lite the only type of class descriptions allowed as objects of rdfs:range are class names.
4.2 Relations to other properties
4.2.1 owl:equivalentProperty
The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_equivalentProperty" owl:equivalentProperty construct can be used to state that two properties have the same property extension. Syntactically, owl:equivalentProperty is a built-in OWL property with rdf:Property as both its domain and range.
NOTE: Property equivalence is not the same as property equality. Equivalent properties have the same "values" (i.e., the same property extension), but may have different intensional meaning (i.e., denote different concepts). Property equality should be expressed with the HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" owl:sameAs construct. As this requires that properties are treated as individuals, such axioms are only allowed in OWL Full.
4.2.2 owl:inverseOf
Properties have a direction, from domain to range. In practice, people often find it useful to define relations in both directions: persons own cars, cars are owned by persons. The HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_inverseOf" owl:inverseOf construct can be used to define such an inverse relation between properties.
Syntactically, owl:inverseOf is a built-in OWL property with owl:ObjectProperty as its domain and range. An axiom of the form P1 owl:inverseOf P2 asserts that for every pair (x,y) in the property extension of P1, there is a pair (y,x) in the property extension of P2, and vice versa. Thus, owl:inverseOf is a symmetric property.
An example:
4.3 Global cardinality constraints on properties
4.3.1 owl:FunctionalProperty
A functional property is a property that can have only one (unique) value y for each instance x, i.e. there cannot be two distinct values y1 and y2 such that the pairs (x,y1) and (x,y2) are both instances of this property. Both object properties and datatype properties can be declared as "functional". For this purpose, OWL defines the built-in class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_FunctionalProperty" owl:FunctionalProperty as a special subclass of the RDF class rdf:Property.
The following axiom states that the husband property is functional, i.e., a woman can have at most one husband (a good example of culture dependence of ontologies):
As always, there are syntactic variations. The example above is semantically equivalent to the one below:
4.3.2 owl:InverseFunctionalProperty
If a property is declared to be inverse-functional, then the object of a property statement uniquely determines the subject (some individual). More formally, if we state that P is an owl:InverseFunctionalProperty, then this asserts that a value y can only be the value of P for a single instance x, i.e. there cannot be two distinct instances x1 and x2 such that both pairs (x1,y) and (x2,y) are instances of P.
Syntactically, an inverse-functional property axiom is specified by declaring the property to be an instance of the built-in OWL class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_InverseFunctionalProperty" owl:InverseFunctionalProperty, which is a subclass of the OWL class owl:ObjectProperty.
NOTE: Because in OWL Full datatype properties are a subclass of object properties, an inverse-functional property can be defined for datatype properties. In OWL DL object properties and datatype properties are disjoint, so an inverse-functional property cannot be defined for datatype properties. See also HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLFull" Sec. 8.1 and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLDL" Sec. 8.2.
A typical example of an inverse-functional property:
This example states that for each object of biologicalMotherOf statements (some human) one should be able to uniquely identify a subject (some woman). Inverse-functional properties resemble the notion of a key in databases.
One difference with functional properties is that for inverse-functional properties no additional object-property or datatype-property axiom is required: inverse-functional properties are by definition object properties.
Notice that HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "FunctionalProperty-def" owl:FunctionalProperty and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" owl:InverseFunctionalProperty specify global cardinality constraints. That is, no matter which class the property is applied to, the cardinality constraints must hold. This is different from the cardinality constraints contained in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Restriction" property restrictions. The latter are class descriptions and are only enforced on the property when applied to that class.
4.4 Logical characteristics of properties
4.4.1 owl:TransitiveProperty
When one defines a property P to be a transitive property, this means that if a pair (x,y) is an instance of P, and the pair (y,z) is also instance of P, then we can infer the the pair (x,z) is also an instance of P.
Syntactically, a property is defined as being transitive by making it an instance of the the built-in OWL class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_TransitiveProperty" owl:TransitiveProperty, which is defined as a subclass of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ObjectProperty-def" owl:ObjectProperty.
Typical examples of transitive properties are properties representing certain part-whole relations. For example, we might want to say that the subRegionOf property between regions is transitive:
From this an OWL reasoner should be able to derive that if ChiantiClassico, Tuscany and Italy are regions, and ChiantiClassico is a subregion of Tuscany, and Tuscany is a subregion of Italy, then ChiantiClassico is also a subregion of Italy.
Note that because owl:TransitiveProperty is a subclass of owl:ObjectProperty, the following syntactic variant is equivalent to the example above:
NOTE: OWL DL requires that for a transitive property no local or global cardinality constraints should be declared on the property itself or its superproperties, nor on the inverse of the property or its superproperties.
4.4.2 owl:SymmetricProperty
A symmetric property is a property for which holds that if the pair (x,y) is an instance of P, then the pair (y,x) is also an instance of P. Syntactically, a property is defined as symmetric by making it an instance of the built-in OWL class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_SymmetricProperty" owl:SymmetricProperty, a subclass of HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ObjectProperty-def" owl:ObjectProperty.
A popular example of a symmetric property is the friendOf relation:
The domain and range of a symmetric property are the same.
5. Individuals
Individuals are defined with individual axioms (also called "facts"). We discuss two types of facts:
Facts about class membership and property values of individuals
Facts about individual identity
5.1 Class membership and property values
Many facts typically are statements indicating class membership of individuals and property values of individuals. As an example, consider the following set of statements about an instance of the class Opera:
1900-01-14
3
This example includes a number of facts about the individual Tosca, an instance of the class Opera. Tosca is composed by Giacomo Puccini. The opera has three libretto writers. The property premiereDate links an opera to a typed literal with the XML Schema datatype date. The XML schema document on datatypes [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-xml-schema2" XML Schema Datatypes] contains the relevant information about syntax and semantics of this datatype.
Individual axioms need not necessarily be about named individuals: they can also refer to anonymous individuals. As an example, consider the piece of RDF/XML below. The example defines some facts about an anonymous instance of the class Measurement, a quantitative observation for which facts such as the subject under observation, the observed phenomenon, the observed value, and the observation time are listed:
59.5
2003-01-24T09:00:08+01:00
This individual axiom contains two anonymous individuals, namely some Measurement and some Quantity. In natural language, for the subject Jane Doe the measured value of the phenomenon Weight is some quantity, which has a value of 59.5 using the unit of kilogram. The time of measurement is January 24, 2003, eight seconds past nine in the morning, in the time zone UTC+1 (winter time in Amsterdam, Berlin, Paris). As before, float and dateTime are XML Schema datatypes, the syntactic and semantic details of which can be found in the relevant XML Schema documentation [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-xml-schema2" XML Schema Datatypes].
5.2 Individual identity
Many languages have a so-called "unique names" assumption: different names refer to different things in the world. On the web, such an assumption is not possible. For example, the same person could be referred to in many different ways (i.e. with different URI references). For this reason OWL does not make this assumption. Unless an explicit statement is being made that two URI references refer to the same or to different individuals, OWL tools should in principle assume either situation is possible.
OWL provides three constructs for stating facts about the identity of individuals:
owl:sameAs is used to state that two URI references refer to the same individual.
owl:differentFrom is used to state that two URI references refer to different individuals
owl:AllDifferent provides an idiom for stating that a list of individuals are all different.
5.2.1 owl:sameAs
The built-in OWL property HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_sameAs" owl:sameAs links an individual to an individual. Such an owl:sameAs statement indicates that two URI references actually refer to the same thing: the individuals have the same "identity".
For individuals such as "people" this notion is relatively easy to understand. For example, we could state that the following two URI references actually refer to the same person:
The owl:sameAs statements are often used in defining mappings between ontologies. It is unrealistic to assume everybody will use the same name to refer to individuals. That would require some grand design, which is contrary to the spirit of the web.
In OWL Full, where a class can be treated as instances of (meta)classes, we can use the owl:sameAs construct to define class equality, thus indicating that two concepts have the same intensional meaning. An example:
One could imagine this axiom to be part of a European sports ontology. The two classes are treated here as individuals, in this case as instances of the class owl:Class. This allows us to state that the class FootballTeam in some European sports ontology denotes the same concept as the class SoccerTeam in some American sports ontology. Note the difference with the statement:
which states that the two classes have the same class extension, but are not (necessarily) the same concepts.
NOTE: For details of comparison of URI references, see the section on RDF URI references in the RDF Concepts document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts].
5.2.2 owl:differentFrom
The built-in OWL HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_differentFrom" owl:differentFrom property links an individual to an individual. An owl:differentFrom statement indicates that two URI references refer to different individuals.
An example:
This states that there are three different operas.
5.2.3 owl:AllDifferent
For ontologies in which the unique-names assumption holds, the use of owl:differentFrom is likely to lead to a large number of statements, as all individuals have to be declared pairwise disjoint. For such situations OWL provides a special idiom in the form of the construct HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_AllDifferent" owl:AllDifferent. owl:AllDifferent is a special built-in OWL class, for which the property HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_distinctMembers" owl:distinctMembers is defined, which links an instance of owl:AllDifferent to a list of individuals. The intended meaning of such a statement is that all individuals in the list are all different from each other.
An example:
This states that these six URI references all point to different operas.
NOTE: owl:distinctMembers is a special syntactical construct added for convenience and should always be used with an owl:AllDifferent individual as its subject.
6. Datatypes
In a number of places in this document we have seen the notion of a data range for specifying a range of data values. OWL allows three types of data range specifications:
A HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "rdf-datatype" RDF datatype specification.
The RDFS class HYPERLINK "http://www.w3.org/TR/rdf-schema/" \l "ch_literal" rdfs:Literal.
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedDatatype" enumerated datatype, using the owl:oneOf construct.
The minimal level of tool support for datatypes is discussed in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeSupport" Sec. 6.3.
6.1 RDF Datatypes
OWL makes use of the RDF datatyping scheme, which provides a mechanism for referring to XML Schema datatypes [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-xml-schema2" XML Schema Datatypes]. For a detailed description the reader is referred to the RDF documents, e.g., [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts]. For the convenience of the reader, we provide here a synopsis of the use of RDF datatypes.
Data values are instances of the RDF Schema class rdfs:Literal. Literals can be either plain (no datatype) or typed. Datatypes are instances of the class rdfs:Datatype. In RDF/XML, the type of a literal is specified by an rdf:datatype attribute of which the value is recommended to be one of the following:
A canonical URI reference to an XML Schema datatype of the form:
http://www.w3.org/2001/XMLSchema#NAME
where "NAME" should be the name of a simple XML Schema built-in datatype, as defined in Section 3 of [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-xml-schema2" XML Schema Datatypes], with the provisos specified below.
The URI reference of the datatype rdf:XMLLiteral. This datatype is used to include XML content into an RDF/OWL document. The URI reference of this datatype is:
http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral
For details about this datatype, see the RDF Concepts document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-concepts" RDF Concepts].
The RDF Semantics document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-RDF-Semantics" RDF Semantics, Section 5]. recommends use of the following simple built-in XML Schema datatypes.
The primitive datatype HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "string" xsd:string, plus the following datatypes derived from xsd:string: HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "normalizedString" xsd:normalizedString, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "token" xsd:token, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "language" xsd:language, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "NMTOKEN" xsd:NMTOKEN, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "Name" xsd:Name,and HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "NCName" xsd:NCName.
The primitive datatype HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "boolean" xsd:boolean.
The primitive numerical datatypes HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "decimal" xsd:decimal, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "float" xsd:float, and HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "double" xsd:double, plus all derived types of xsd:decimal ( HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "integer" xsd:integer, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "positiveInteger" xsd:positiveInteger. HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "nonPositiveInteger" xsd:nonPositiveInteger, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "negativeInteger" xsd:negativeInteger, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "nonNegativeInteger" xsd:nonNegativeInteger, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "long" xsd:long, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "int" xsd:int, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "short" xsd:short, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "byte" xsd:byte, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "unsignedLong" xsd:unsignedLong, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "unsignedInt" xsd:unsignedInt, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "unsignedShort" xsd:unsignedShort, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "unsignedByte" xsd:unsignedByte)
The primitive time-related datatypes: HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "dateTime" xsd:dateTime, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "time" xsd:time, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "date" xsd:date, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "gYearMonth" xsd:gYearMonth, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "gYear" xsd:gYear, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "gMonthDay" xsd:gMonthDay, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "gDay" xsd:gDay, and HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "gMonth" xsd:gMonth.
The primitive datatypes HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "hexBinary" xsd:hexBinary, HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "base64Binary" xsd:base64Binary, and HYPERLINK "http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/" \l "anyURI" xsd:anyURI.
NOTE: It is not illegal, although not recommended, for applications to define their own datatypes by defining an instance of rdfs:Datatype. Such datatypes are "unrecognized", but are treated in a similar fashion as "unsupported datatypes" (see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeSupport" Sec. 6.3 for details about how these should be treated by OWL tools).
When using datatypes, please note that even if a property is defined to have a range of a certain datatype, RDF/XML still requires that the datatype be specified each time the property is used. An example could be the declaration of a property that we used earlier in the Measurement example:
2003-01-24T09:00:08+01:00
6.2 Enumerated datatype
In addition to the RDF datatypes, OWL provides one additional construct for defining a range of data values, namely an enumerated datatype. This datatype format makes use of the owl:oneOf construct, that is also used for describing an HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedClass" enumerated class. In the case of an enumerated datatype, the subject of owl:oneOf is a blank node of class owl:DataRange and the object is a list of literals. Unfortunately, we cannot use the rdf:parseType="Collection" idiom for specifying the literal list, because RDF requires the collection to be a list of RDF node elements. Therefore we have to specify the list of data values with the basic list constructs rdf:first, rdf:rest and rdf:nil.
NOTE: Enumerated datatypes are not part of OWL Lite.
The example below specifies the range of the property tennisGameScore to be the list of integer values {0, 15, 30, 40}:.
0
15
30
40
6.3 Support for datatype reasoning
Tools may vary in terms of support for datatype reasoning. As a minimum, tools must support datatype reasoning for the XML Schema datatypes xsd:string and xsd:integer. OWL Full tools must also support rdf:XMLLiteral. For unsupported datatypes, lexically identical literals should be considered equal, whereas lexically different literals would not be known to be either equal or unequal. Unrecognized datatypes should be treated in the same way as unsupported datatypes.
7. Annotations, ontology header, imports and version information
7.1 Annotations
OWL Full does not put any constraints on annotations in an ontology. OWL DL allows annotations on classes, properties, individuals and ontology headers, but only under the following conditions:
The sets of object properties, datatype properties, annotation properties and ontology properties must be mutually disjoint. Thus, in OWL DL dc:creator cannot be at the same time a datatype property and an annotation property.
Annotation properties must have an explicit typing triple of the form:
AnnotationPropertyID rdf:type owl:AnnotationProperty .
Annotation properties must not be used in property axioms. Thus, in OWL DL one cannot define subproperties or domain/range constraints for annotation properties.
The object of an annotation property must be either a data literal, a URI reference, or an individual.
Five annotation properties are predefined by OWL, namely:
owl:versionInfo
rdfs:label
rdfs:comment
rdfs:seeAlso
rdfs:isDefinedBy
Here is an example of legal use of an annotation property in OWL DL:
Musical work
N.N.
The example assumes &dc; and dc: point respectively to the Dublin Core URI and namespace. Thus, using Dublin Core properties as annotation properties in OWL DL requires an explicit typing triple. This ensures annotations are handled in a semantically correct fashion by OWL DL reasoners (see the OWL Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS] for details).
Once we define dc:creator as an annotation property, OWL DL does NOT allow property axioms such as the range constraint below:
<-- This is illegal in OWL DL -->
Note that one can still specify the value type of a literal in an annotation-property statement:
Giacomo Puccini
7.2 Ontology header
A document describing an ontology typically contains information about the ontology itself. An ontology is a resource, so it may be described using properties from the OWL and other namespaces, e.g.:
...
...
This is commonly called the ontology header and is typically found near the beginning of the RDF/XML document. The line
states that this block describes the current ontology. More precisely, it states the current base URI identifies an instance of the class owl:Ontology. It is recommended that the base URI be defined using an xml:base attribute in the element at the beginning of the document.
A sample ontology header could look like this:
v 1.17 2003/02/26 12:56:51 mdean
An example ontology
The following sections describe the various types of statements that are typically used within the header.
NOTE: The ontology-import construct HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "imports-def" owl:imports and the ontology-versioning constructs HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "priorVersion-def" owl:priorVersion, HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "backwardCompatibleWith-def" owl:backwardCompatibleWith and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "incompatibleWith-def" owl:incompatibleWith are defined in the OWL vocabulary as instances of the OWL built-in class owl:OntologyProperty. Instances of owl:OntologyProperty must have the class owl:Ontology as their domain and range. It is permitted to define other instances of owl:OntologyProperty. In OWL DL for ontology properties the same constraints hold as those specified for annotation properties in HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Annotations" Sec. 7.1.
7.3 Importing an ontology
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_imports" owl:imports statement references another OWL ontology containing definitions, whose meaning is considered to be part of the meaning of the importing ontology. Each reference consists of a URI specifying from where the ontology is to be imported. Syntactically, owl:imports is a property with the class owl:Ontology as its domain and range.
The owl:imports statements are transitive, that is, if ontology A imports B, and B imports C, then A imports both B and C.
Importing an ontology into itself is considered a null action, so if ontology A imports B and B imports A, then they are considered to be equivalent.
Note that whether or not an OWL tool must load an imported ontology depends on the purpose of the tool. If the tool is a complete reasoner (including complete consistency checkers) then it must load all of the imported ontologies. Other tools, such as simple editors and incomplete reasoners, may choose to load only some or even none of the imported ontologies.
Although owl:imports and namespace declarations may appear redundant, they actually serve different purposes. Namespace declarations simply set up a shorthand for referring to identifiers. They do not implicitly include the meaning of documents located at the URI. On the other hand, owl:imports does not provide any shorthand notation for referring to the identifiers from the imported document. Therefore, it is common to have a corresponding namespace declaration for any ontology that is imported.
NOTE: owl:imports is an instance of owl:OntologyProperty.
7.4 Version information
7.4.1 owl:versionInfo
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_versionInfo" owl:versionInfo statement generally has as its object a string giving information about this version, for example RCS/CVS keywords. This statement does not contribute to the logical meaning of the ontology other than that given by the RDF(S) model theory.
Although this property is typically used to make statements about ontologies, it may be applied to any OWL construct. For example, one could attach a owl:versionInfo statement to an OWL class.
NOTE: owl:versionInfo is an instance of owl:AnnotationProperty.
7.4.2 owl:priorVersion
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_priorVersion" owl:priorVersion statement contains a reference to another ontology. This identifies the specified ontology as a prior version of the containing ontology. This has no meaning in the model-theoretic semantics other than that given by the RDF(S) model theory. However, it may be used by software to organize ontologies by versions.
owl:priorVersion is a built-in OWL property with the class owl:Ontology as its domain and range.
NOTE: owl:priorVersion is an instance of owl:OntologyProperty.
7.4.3 owl:backwardCompatibleWith
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_backwardCompatibleWith" owl:backwardCompatibleWith statement contains a reference to another ontology. This identifies the specified ontology as a prior version of the containing ontology, and further indicates that it is backward compatible with it. In particular, this indicates that all identifiers from the previous version have the same intended interpretations in the new version. Thus, it is a hint to document authors that they can safely change their documents to commit to the new version (by simply updating namespace declarations and HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "imports-def" owl:imports statements to refer to the URL of the new version). If owl:backwardCompatibleWith is not declared for two versions, then compatibility should not be assumed.
owl:backwardCompatibleWith has no meaning in the model theoretic semantics other than that given by the RDF(S) model theory.
owl:backwardCompatibleWith is a built-in OWL property with the class owl:Ontology as its domain and range.
NOTE: owl:backwardCompatibleWith is an instance of owl:OntologyProperty.
7.4.4 owl:incompatibleWith
An HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_incompatibleWith" owl:incompatibleWith statement contains a reference to another ontology. This indicates that the containing ontology is a later version of the referenced ontology, but is not backward compatible with it. Essentially, this is for use by ontology authors who want to be explicit that documents cannot upgrade to use the new version without checking whether changes are required.
owl:incompatibleWith has no meaning in the model theoretic semantics other than that given by the RDF(S) model theory.
owl:incompatibleWith is a built-in OWL property with the class owl:Ontology as its domain and range.
NOTE: owl:backwardCompatibleWith is an instance of owl:OntologyProperty.
7.4.5 owl:DeprecatedClass and owl:DeprecatedProperty
Deprecation is a feature commonly used in versioning software (for example, see the Java programming language) to indicate that a particular feature is preserved for backward-compatibility purposes, but may be phased out in the future. Here, a specific identifier is said to be of type HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DeprecatedClass" owl:DeprecatedClass or HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DeprecatedProperty" owl:DeprecatedProperty, where owl:DeprecatedClass is a subclass of rdfs:Class and owl:DeprecatedProperty is a subclass of rdf:Property. By deprecating a term, it means that the term should not be used in new documents that commit to the ontology. This allows an ontology to maintain backward-compatibility while phasing out an old vocabulary (thus, it only makes sense to use deprecation in combination with backward compatibility). As a result, it it easier for old data and applications to migrate to a new version, and thus can increase the level of adoption of the new version. This has no meaning in the model theoretic semantics other than that given by the RDF(S) model theory. However, authoring tools may use it to warn users when checking OWL markup.
An example of deprecation is:
Vehicle Ontology, v. 1.1
Automobile is now preferred
inverse property drives is now preferred
8. OWL Full, OWL DL and OWL Lite
In the introduction we briefly discussed the three sublanguages of OWL. In this section an informative specification is given of the differences between the three "species" of OWL. A formal account of the differences is given in the Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS].
8.1 OWL Full
OWL Full is not actually a sublanguage. OWL Full contains all the OWL language constructs and provides free, unconstrained use of RDF constructs. In OWL Full the resource owl:Class is equivalent to rdfs:Class. This is different from OWL DL and OWL Lite, where owl:Class is a proper subclass of rdfs:Class (meaning that not all RDF classes are OWL classes in OWL DL and OWL Lite). OWL Full also allows classes to be treated as individuals. For example, it is perfectly legal in OWL Full to have a "Fokker-100" identifier which acts both as a class name (denoting the set of Fokker-100 airplanes flying around the world) and as an individual name (e.g., an instance of the class AirplaneType).
In OWL Full all data values are considered also to be part of the individual domain. In fact, in OWL Full the universe of individuals consists of all resources (owl:Thing is equivalent to rdfs:Resource). This means that object properties and datatype properties are not disjoint. In OWL Full owl:ObjectProperty is equivalent to rdf:Property. The consequence is that datatype properties are effectively a subclass of object properties. (Note: the fact that owl:ObjectProperty and owl:DatatypeProperty are both subclasses of rdf:Property is not inconsistent with this).
OWL Full will typically be useful for people who want to combine the expressivity of OWL with the flexibility and metamodelling features of RDF. However, use of the OWL Full features means that one loses some guarantees (see HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OWLDL" below) that OWL DL and OWL Lite can provide for reasoning systems.
NOTE: RDF documents will generally be in OWL Full, unless they are specifically constructed to be in OWL DL or Lite.
NOTE: Thus, in OWL Full owl:Thing is equivalent to rdfs:Resource, owl:Class is equivalent to rdfs:Class, and owl:ObjectProperty is equivalent to rdf:Property,
8.2 OWL DL
OWL DL is a sublanguage of OWL which places a number of constraints on the use of the OWL language constructs. Briefly, these constraints are the following:
OWL DL requires a pairwise separation between classes, datatypes, datatype properties, object properties, annotation properties, ontology properties (i.e., the import and versioning stuff), individuals, data values and the built-in vocabulary. This means that, for example, a class cannot be at the same time an individual.
In OWL DL the set of object properties and datatype properties are disjoint. This implies that the following four property characteristics:
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "inverseOf-def" inverse of,
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" inverse functional,
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "SymmetricProperty-def" symmetric, and
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "TransitiveProperty-def" transitive
can never be specified for HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeProperty-def" datatype properties
OWL DL requires that no cardinality constraints (local nor global) can be placed on transitive properties or their inverses or any of their superproperties.
Annotations are allowed only under certain conditions. See HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Annotations" Sec. 7.1 for details.
Most RDF(S) vocabulary cannot be used within OWL DL. See the OWL Semantics and Abstract Syntax document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL S&AS] for details.
All axioms must be well-formed, with no missing or extra components, and must form a tree-like structure.
The last constraint implies that all classes and properties that one refers to are explicitly typed as OWL classes or properties, respectively. For example, if the ontology contains the following component:
then the ontology (or an ontology imported into this ontology) should contain a owl:Class triple for C2.
Axioms (facts) about individual equality and difference must be about named individuals.
These constraints of OWL DL may seem like an arbitrary set, but in fact they are not. The constraints are based on work in the area of reasoners for Description Logic, which require these restrictions to provide the ontology builder or user with reasoning support. In particular, the OWL DL restrictions allow the maximal subset of OWL Full against which current research can assure that a decidable reasoning procedure can exist for an OWL reasoner.
NOTE: HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "app-DLinRDF" Appendix E provides a set of practical guidelines for specifying OWL DL ontologies in RDF.
8.3 OWL Lite
OWL Lite abides by all the restrictions OWL DL puts on the use of the OWL language constructs. In addition, OWL Lite forbids the use of:
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "oneOf-def" owl:oneOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" owl:unionOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "complementOf-def" owl:complementOf
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "hasValue-def" owl:hasValue
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "disjointWith-def" owl:disjointWith
HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DataRange-def" owl:DataRange
OWL Lite also requires that:
the subject of owl:equivalentClass triples be class names and the object of owl:equivalentClass triples be class names or restrictions.
the subject of rdfs:subClassOf triples be class names and the object of rdfs:subClassOf triples be class names or restrictions;
owl:intersectionOf be used only on lists of length greater than one that contain only class names and restrictions;
NOTE: This is a prototypical example of legal use of owl:intersectionOf in OWL Lite:
the object of owl:allValuesFrom and owl:someValuesFrom triples be class names or datatype names;
the object of rdf:type triples be class names or restrictions;
the object of rdfs:domain triples be class names; and
the object of rdfs:range triples be class names or datatype names.
The idea behind the OWL Lite expressivity limitations is that they provide a minimal useful subset of language features, that are relatively straightforward for tool developers to support. The language constructs of OWL Lite provide the basics for subclass hierarchy construction: subclasses and property restrictions. In addition, OWL Lite allows properties to be made optional or required. The limitations on OWL Lite place it in a lower complexity class than OWL DL. This can have a positive impact on the efficiency of complete reasoners for OWL Lite.
Implementations that support only the OWL Lite vocabulary, but otherwise relax the restrictions of OWL DL, cannot make certain computational claims with respect to consistency and complexity. However, such implementations may be useful in providing interoperability of OWL systems with RDFS models, databases, markup tools, or other non-reasoning tools. The Web Ontology Working Group has not provided a name for this potentially useful subset.
Appendix A. Index of all language elements
NOTE: This appendix only contains the OWL-specific constructs. For the RDF/RDFS constructs see the relevant RDF documentation, in particular the RDF Schema document [ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-rdf-vocabulary" RDF Vocabulary].
[OWL Reference](this document)[ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-abstract-syntax" OWL Semantics](normative)[ HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ref-owl-guide" OWL Guide](examples) HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "AllDifferent-def" owl:AllDifferent HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_AllDifferent" owl:AllDifferent HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_AllDifferent" owl:AllDifferent HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "allValuesFrom-def" owl:allValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_allValuesFrom" owl:allValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_allValuesFrom" owl:allValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "AnnotationProperty-def" owl:AnnotationProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_AnnotationProperty" owl:AnnotationProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "backwardCompatibleWith-def" owl:backwardCompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_backwardCompatibleWith" owl:backwardCompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_backwardCompatibleWith" owl:backwardCompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "cardinality-def" owl:cardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_cardinality" owl:cardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_cardinality" owl:cardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Class-def" owl:Class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Class" owl:Class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_Class" owl:Class HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "complementOf-def" owl:complementOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_complementOf" owl:complementOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_complementOf" owl:complementOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "EnumeratedDatatype" owl:DataRange HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DataRange" owl:DataRange HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DatatypeProperty-def" owl:DatatypeProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DatatypeProperty" owl:DatatypeProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_DatatypeProperty" owl:DatatypeProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DeprecatedClass-def" owl:DeprecatedClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DeprecatedClass" owl:DeprecatedClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_DeprecatedClass" owl:DeprecatedClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "DeprecatedProperty-def" owl:DeprecatedProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_DeprecatedProperty" owl:DeprecatedProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_DeprecatedProperty" owl:DeprecatedProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "differentFrom-def" owl:differentFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_differentFrom" owl:differentFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_differentFrom" owl:differentFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "disjointWith-def" owl:disjointWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_disjointWith" owl:disjointWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_disjointWith" owl:disjointWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "distinctMembers-def" owl:distinctMembers HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_distinctMembers" owl:distinctMembers HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_distinctMembers" owl:distinctMembers HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentClass-def" owl:equivalentClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_equivalentClass" owl:equivalentClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_equivalentClass" owl:equivalentClass HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "equivalentProperty-def" owl:equivalentProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_equivalentProperty" owl:equivalentProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_equivalentProperty" owl:equivalentProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "FunctionalProperty-def" owl:FunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_FunctionalProperty" owl:FunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_FunctionalProperty" owl:FunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "hasValue-def" owl:hasValue HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_hasValue" owl:hasValue HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_hasValue" owl:hasValue HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "imports-def" owl:imports HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_imports" owl:imports HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_imports" owl:imports HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "incompatibleWith-def" owl:incompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_incompatibleWith" owl:incompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_incompatibleWith" owl:incompatibleWith HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "intersectionOf-def" owl:intersectionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_intersectionOf" owl:intersectionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_intersectionOf" owl:intersectionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "InverseFunctionalProperty-def" owl:InverseFunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_InverseFunctionalProperty" owl:InverseFunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_InverseFunctionalProperty" owl:InverseFunctionalProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "inverseOf-def" owl:inverseOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_inverseOf" owl:inverseOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_inverseOf" owl:inverseOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "maxCardinality-def" owl:maxCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_maxCardinality" owl:maxCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_maxCardinality" owl:maxCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "minCardinality-def" owl:minCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_minCardinality" owl:minCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_minCardinality" owl:minCardinality HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Nothing-def" owl:Nothing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Nothing" owl:Nothing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_Nothing" owl:Nothing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "ObjectProperty-def" owl:ObjectProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_ObjectProperty" owl:ObjectProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_ObjectProperty" owl:ObjectProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "oneOf-def" owl:oneOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_oneOf" owl:oneOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_oneOf" owl:oneOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "onProperty-def" owl:onProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_onProperty" owl:onProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_onProperty" owl:onProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Ontology-def" owl:Ontology HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Ontology" owl:Ontology HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_Ontology" owl:Ontology HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "OntologyProperty-def" owl:OntologyProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_OntologyProperty" owl:OntologyProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "priorVersion-def" owl:priorVersion HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_priorVersion" owl:priorVersion HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_priorVersion" owl:priorVersion HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Restriction-def" owl:Restriction HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Restriction" owl:Restriction HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_Restriction" owl:Restriction HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "sameAs-def" owl:sameAs HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_sameAs" owl:sameAs HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_sameAs" owl:sameAs HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "someValuesFrom-def" owl:someValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_someValuesFrom" owl:someValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_someValuesFrom" owl:someValuesFrom HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "SymmetricProperty-def" owl:SymmetricProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_SymmetricProperty" owl:SymmetricProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_SymmetricProperty" owl:SymmetricProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "Thing-def" owl:Thing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_Thing" owl:Thing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_Thing" owl:Thing HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "TransitiveProperty-def" owl:TransitiveProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_TransitiveProperty" owl:TransitiveProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_TransitiveProperty" owl:TransitiveProperty HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "unionOf-def" owl:unionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_unionOf" owl:unionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_unionOf" owl:unionOf HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "versionInfo-def" owl:versionInfo HYPERLINK "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/" \l "owl_versionInfo" owl:versionInfo HYPERLINK "http://www.w3.org/TR/2004/REC-owl-guide-20040210/" \l "owl_versionInfo" owl:versionInfoAppendix B. RDF Schema of OWL
See HYPERLINK "http://www.w3.org/TR/2004/REC-owl-ref-20040210/" \l "AppendixList" Sec. 1.7 for a description of the purpose of this appendix. The RDF/XML version of this appendix can be found at HYPERLINK "http://www.w3.org/2002/07/owl" http://www.w3.org/2002/07/owl
]>
This file specifies in RDF Schema format the
built-in classes and properties that together form the basis of
the RDF/XML syntax of OWL Full, OWL DL and OWL Lite.
We do not expect people to import this file
explicitly into their ontology. People that do import this file
should expect their ontology to be an OWL Full ontology.
10 February 2004
Class
Thing
Nothing
equivalentClass
disjointWith
equivalentProperty
sameAs
differentFrom
AllDifferent
distinctMembers
unionOf
intersectionOf
complementOf
oneOf
Restriction
onProperty
allValuesFrom
hasValue
someValuesFrom
minCardinality
maxCardinality
cardinality
ObjectProperty
DatatypeProperty
inverseOf
TransitiveProperty
SymmetricProperty
FunctionalProperty
InverseFunctionalProperty