W3C

OWL Web Ontology Language
Semantics and Abstract Syntax

W3C Candidate Recommendation 18 August 2003

This version:
http://www.w3.org/TR/2003/CR-owl-semantics-20030818/
Latest version:
http://www.w3.org/TR/owl-semantics/
Previous version:
http://www.w3.org/TR/2003/WD-owl-semantics-20030331/
Editors:
Peter F. Patel-Schneider, Bell Labs Research, Lucent Technologies
Patrick Hayes, IHMC, University of West Florida
Ian Horrocks, Department of Computer Science, University of Manchester

This document is also available in this non-normative form: single HTML file.

Copyright © 2003 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.

Abstract

This description of OWL, the Web Ontology Language being designed by the W3C Web Ontology Working Group, contains a high-level abstract syntax for both OWL DL and OWL Lite, sublanguages of OWL. A model-theoretic semantics is given to provide a formal meaning for OWL ontologies written in this abstract syntax. A model-theoretic semantics in the form of an extension to the RDF semantics is also given to provide a formal meaning for OWL ontologies as RDF graphs (OWL Full). A mapping from the abstract syntax to RDF graphs is given and the two model theories are shown to have the same consequences on OWL ontologies that can be written in the abstract syntax.

Status of this document

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 W3C technical reports index at http://www.w3.org/TR/.

Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than "work in progress".

This draft is one of six parts of the Candidate Recommendation (CR) for OWL, the Web Ontology Language. It has been developed by the Web Ontology Working Group as part of the W3C Semantic Web Activity (Activity Statement, Group Charter) for publication on 18 August 2003.

The design of OWL expressed in earlier versions of these documents has been widely reviewed and satisfies the Working Group's technical requirements. The Working Group has addressed all comments received, making changes as necessary. Changes to this document since the Last Call Working Draft are detailed in the change log.

The Working Group now hopes to gather experience from the growing number of OWL implementations in order to increase confidence in the language and meet specific exit criteria. This CR period will extend until at least 20 September 2003. After that date, when and if the exit criteria are met, the group intends to request Proposed Recommendation status.

Please send reports of implementation experience to public-webont-comments@w3.org (archive). Reports of any success or difficulty with the Test Cases are encouraged, and reports received by 20 September 2003 will be particularly helpful. General discussion of related technology is welcome at www-rdf-logic@w3.org (archive).

Although OWL is essentially stable, later versions of these documents are expected to contain minor improvements. The test site is likely to include new, clarifying tests, even during this CR period. Additionally, the design of OWL depends in part on the design of RDF, and at this time the relevant RDF specifications are only Working Drafts. It is therefore possible that unanticipated changes in RDF may require changes to OWL. This document is current with respect to RDF Editor's Draft changes made up to 7 August 2003.

One technical detail concerning structure reuse in Section 4 (Mapping to RDF Graphs) has been identified as "at risk" and subject to change. We expect this change, if made, to simplify rather than complicate implementations, and since it is a relaxation of a current restriction, it will not invalidate or change the meaning of any valid OWL or RDF documents.

The W3C maintains a list of any patent disclosures related to this work.

Table of contents

1. Introduction (Informative)

This document is one part of the specification of OWL, the Web Ontology Language. The OWL Overview [OWL Overview] describes each of the different documents in the specification and how they fit together.

This document contains several interrelated normative specifications of the several styles of OWL, the Web Ontology Language being produced by the W3C Web Ontology Working Group (WebOnt). First, Section 2 contains a high-level, abstract syntax for both OWL Lite, a subset of OWL, and OWL DL, a fuller style of using OWL but one that still places some limitations on how OWL ontologies are constructed. Eliminating these limitations results in the full OWL language, called OWL Full, which has the same syntax as RDF. The normative exchange syntax for OWL is RDF/XML [RDF Syntax]; the OWL Reference document [OWL Reference] shows how the RDF syntax is used in OWL. A mapping from the OWL abstract syntax to RDF graphs [RDF Concepts] is, however, provided in Section 4.

This document contains two formal semantics for OWL. One of these semantics, defined in Section 3, is a direct, standard model-theoretic semantics for OWL ontologies written in the abstract syntax. The other, defined in Section 5, is a vocabulary extension of the RDF semantics [RDF MT] that provides semantics for OWL ontologies in the form of RDF graphs. Two versions of this second semantics are provided, one that corresponds more closely to the direct semantics (and is thus a semantics for OWL DL) and one that can be used in cases where classes need to be treated as individuals or other situations that cannot be handled in the abstract syntax (and is thus a semantics for OWL Full). These two versions are actually very close, only differing in how they divide up the domain of discourse.

Appendix A contains a proof that the direct and RDFS-compatible semantics have the same consequences on OWL ontologies that correspond to abstract OWL ontologies that separate OWL individuals, OWL classes, OWL properties, and the RDF, RDFS, and OWL structural vocabulary. Appendix A also contains the sketch of a proof that the entailments in the RDFS-compatible semantics for OWL Full include all the entailments in the RDFS-compatible semantics for OWL DL. Finally a few examples of the various concepts defined in the document are presented in Appendix B.

This document is designed to be read by those interested in the technical details of OWL. It is not particularly intended for the casual reader, who should probably first read the OWL Guide [OWL Guide]. Developers of parsers and other syntactic tools for OWL will be particularly interested in Sections 2 and 4. Developers of reasoners and other semantic tools for OWL will be particulary interested in Sections 3 and 5.

Appendix C. Changes from Last Call (Informative)

This appendix provides an informative account of the changes from the last-call version of this document. Post-last call changes to the document, except for some minor changes to fix formatting, etc., are indicated in the style of this appendix.

C.1 Substantive changes

This section provides information on the changes to the document that make changes to the specification of OWL.

C.2 Editorial changes

This section provides information on editorial changes to the document, i.e., changes that do not affect the specification of OWL.

Index of Vocabulary (Informative)

The following table provides pointers to information about each element of the OWL vocabulary, as well as some elements of the RDF and RDFS vocabularies. The first column points to the vocabulary element's major definition in the abstract syntax of Section 2. The second column points to the vocabulary element's major definition in the OWL Lite abstract syntax. The third column points to the vocabularly element's major definition in the direct semantics of Section 3. The fourth column points to the major piece of the translation from the abstract syntax to triples for the vocabulary element Section 4. The fifth column points to the vocabularly element's major definition in the RDFS-compatible semantics of Section 5.

Vocabulary Terms
Vocabulary Term Abstract OWL DL Syntax Abstract OWL Lite Syntax Direct Semantics Mapping to Triples RDFS-Compatible Semantics
owl:AllDifferent 4.1 5.2
owl:allValuesFrom 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:AnnotationProperty 2.3.1.3 2.3.2.4 3.2 4.1 5.2
owl:backwardCompatibleWith 2.1 2.1 4.1
owl:cardinality 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:Class 2.3.2.1 2.3.1.1 3.3 4.1 5.2
owl:complementOf 2.3.2.2 3.2 4.1 5.2
owl:DatatypeProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:DeprecatedClass 2.3.2.1 2.3.1.1 3.3 4.1 5.2
owl:DeprecatedProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:DataRange 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:differentFrom 2.2 2.2 3.3 4.1 5.2
owl:disjointWith 2.3.2.1 3.3 4.1 5.2
owl:distinctMembers 4.1 5.2
owl:equivalentClass 2.3.2.1 2.3.1.1 3.3 4.1 5.2
owl:equivalentProperty 2.3.1.3 2.3.1.3 3.3 4.1 5.2
owl:FunctionalProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:hasValue 2.3.2.3 3.2 4.1 5.2
owl:imports 2.1 2.1 3.4 4.1 5.4
owl:incompatibleWith 2.1 2.1 4.1
owl:intersectionOf 2.3.2.2 3.2 4.1 5.2
owl:InverseFunctionalProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:inverseOf 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:maxCardinality 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:minCardinality 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:Nothing 2.1 2.1 3.2 4.1 5.2
owl:ObjectProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:oneOf 2.3.2.2 3.2 4.1 5.2
owl:onProperty 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:Ontology 2.1 2.1 3.4 4.1 5.2
owl:OntologyProperty 2.3.1.3 2.3.2.4 3.2 4.1 5.2
owl:priorVersion 2.1 2.1 4.1
owl:Restriction 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:sameAs 2.2 2.2 3.3 4.1 5.2
owl:someValuesFrom 2.3.2.3 2.3.1.2 3.2 4.1 5.2
owl:SymmetricProperty 2.3.2.4 2.3.1.3 3.3 4.1 4.2
owl:Thing 2.1 2.1 3.2 4.1 5.2
owl:TransitiveProperty 2.3.2.4 2.3.1.3 3.3 4.1 5.2
owl:unionOf 2.3.2.2 3.2 4.1 5.2
owl:versionInfo 2.1 2.1 4.1
rdf:List 4.1 5.2
rdf:nil 4.1 5.2
rdf:type 2.2 2.2 3.3 4.1
rdfs:comment 2.1 2.1 4.1
rdfs:Datatype 4.1 5.2
rdfs:domain 2.3.2.4 2.3.1.3 3.3 4.1 5.2
rdfs:label 2.1 2.1 4.1
rdfs:Literal 2.3.1.3 2.3.2.3 4.1 4.1 5.2
rdfs:range 2.3.2.4 2.3.1.3 3.3 4.1 5.2
rdfs:subClassOf 2.3.2.1 2.3.1.1 3.3 4.1 5.2
rdfs:subPropertyOf 2.3.1.3 2.3.1.3 3.3 4.1 5.2

Acknowledgments

The Joint US/EU ad hoc Agent Markup Language Committee developed DAML+OIL, which is the direct precursor to OWL. Many of the ideas in DAML+OIL and thus in OWL are also present in the Ontology Inference Layer (OIL). Many of the other members of the W3C Web Ontology Working Group have had substantial input into this document.

This document is the result of extensive discussions within the Web Ontology Working Group as a whole. The members of this group working group included: Yasser al Safadi, Jean-Francois 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, Jerome Euzenat, Dieter Fensel, Tim Finin, Nicholas Gibbins, Pat Hayes, Jeff Heflin, Ziv Hellman, James Hendler, Bernard Horan, Masahiro Hori, Ian Horrocks, Francesco Iannuzzelli, Mario Jeckle, Ruediger Klein, Natasha Kravtsova, Ora Lassila, Alexander Maedche, Massimo Marchiori, Deborah McGuinness, Libby Miller, Enrico Motta, Leo Obrst, Laurent Olivry , Peter Patel-Schneider, Martin Pike, Marwan Sabbouh, Guus Schreiber, Shimizu Noboru, Michael Sintek, Michael Smith, Ned Smith, John Stanton, Lynn Andrea Stein, Herman ter Horst, Lynne R. Thompson, David Trastour, Frank van Harmelen, Raphael Volz, Evan Wallace, Christopher Welty, Charles White, and John Yanosy.

References

Normative References

[RDF Concepts]
Resource Description Framework (RDF): Concepts and Abstract Syntax. Graham Klyne and Jeremy J. Carroll, eds. W3C Working Draft 23 January 2003. Latest version is available at http://www.w3.org/TR/rdf-concepts/. Significant post-last-call changes to RDF that impact OWL have been made in this document; as of 8 August 2003 these changes can be seen at http://www.w3.org/2001/sw/RDFCore/TR/WD-rdf-concepts-20030117/.
[RDF MT]
RDF Semantics. Patrick Hayes, ed. W3C Working Draft 23 January 2003. Latest version is available at http://www.w3.org/TR/rdf-mt/. Significant post-last-call changes to RDF that impact OWL have been made in this document; as of 8 August 2003 these changes can be seen at http://www.w3.org/2001/sw/RDFCore/TR/WD-rdf-mt-20030117/.
[RDF Syntax]
RDF/XML Syntax Specification (Revised) Dave Beckett, ed. W3C Working Draft 23 January 2003. Latest version is available at http://www.w3.org/TR/rdf-syntax-grammar/.
[RDF Tests]
RDF Test Cases. Jan Grant and Dave Beckett, eds. W3C Working Draft 23 January 2003. Latest version is available at http://www.w3.org/TR/rdf-testcases/. Significant post-last-call changes to RDF that impact OWL have been made in this document; as of 8 August 2003 these changes can be seen at http://www.w3.org/2001/sw/RDFCore/TR/WD-rdf-testcases-20030117/.
[XML]
Extensible Markup Language (XML) 1.0 (Second Edition). Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, and Eve Maler, eds. W3C Recommendation 6 October 2000. Latest version is available at http://www.w3.org/TR/REC-xml.
[XML Schema Datatypes]
XML Schema Part 2: Datatypes.. Paul V. Biron and Ashok Malhotra, eds. W3C Recommendation 02 May 2000. Latest version is available at http://www.w3.org/TR/xmlschema-2/.

Other References

[DAML+OIL]
DAML+OIL (March 2001) Reference Description. Dan Connolly, Frank van Harmelen, Ian Horrocks, Deborah L. McGuinness, Peter F. Patel-Schneider, and Lynn Andrea Stein. W3C Note 18 December 2001. Latest version is available at http://www.w3.org/TR/daml+oil-reference.
[OWL Guide]
OWL Web Ontology Language Guide. Michael K. Smith, and Chris Welty, and Deborah L. McGuinness. W3C Candidate Recommendation 18 August 2003. Latest version is available at http://www.w3.org/TR/owl-guide/.
[OWL Issues]
Web Ontology Issue Status. Michael K. Smith, ed. 27 June 2003.
[OWL Overview]
OWL Web Ontology Language Overview. Deborah L. McGuinness and Frank van Harmelen. W3C Candidate Recommendation 18 August 2003. Latest version is available at http://www.w3.org/TR/owl-features/.
[OWL Reference]
OWL Web Ontology Language Reference. Mike Dean, Guus Schreiber, Sean Bechhofer, Frank van Harmelen, Jim Hendler, Ian Horrocks, Deborah L. McGuinness, Peter F. Patel-Schneider, and Lynn Andrea Stein. W3C Candidate Recommendation 18 August 2003. Latest version is available at http://www.w3.org/TR/owl-ref/.
[RDFMS]
Resource Description Framework (RDF) Model and Syntax Specification. Ora Lassila and Ralph R. Swick, eds. W3C Recommendation 22 February 1999. Latest version is available at http://www.w3.org/TR/REC-rdf-syntax/.
[RDF Schema]
RDF Vocabulary Description Language 1.0: RDF Schema. Dan Brickley and R. V. Guha, eds. W3C Working Draft 23 January 2003. Latest version is available at http://www.w3.org/TR/rdf-schema/.