OWL Web Ontology Language Semantics and Abstract Syntax (original) (raw)

W3C Recommendation 10 February 2004

This version:

http://www.w3.org/TR/2004/REC-owl-semantics-20040210/

Latest version:

http://www.w3.org/TR/owl-semantics/

Previous version:

http://www.w3.org/TR/2003/PR-owl-semantics-20031215/

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

Please refer to the erratafor this document, which may include some normative corrections.

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

See also translations.

Copyright © 2004 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.

Table of contents

• 1. Introduction (Informative)
• 2. Abstract Syntax (Normative)
  • 2.1 Ontologies
  • 2.2 Facts
  • 2.3 Axioms
    * 2.3.1 OWL Lite Axioms
    * 2.3.1.1 OWL Lite Class Axioms
    * 2.3.1.2 OWL Lite Restrictions
    * 2.3.1.3 OWL Lite Property Axioms
    * 2.3.2 OWL DL Axioms
    * 2.3.2.1 OWL DL Class Axioms
    * 2.3.2.2 OWL DL Descriptions
    * 2.3.2.3 OWL DL Restrictions
    * 2.3.2.4 OWL DL Property Axioms
• 3. Direct Model-Theoretic Semantics (Normative)
  • 3.1 Vocabularies and Interpretations
  • 3.2 Interpreting Embedded Constructs
  • 3.3 Interpreting Axioms and Facts
  • 3.4 Interpreting Ontologies
• 4. Mapping to RDF Graphs (Normative)
  • 4.1 Translation to RDF Graphs
  • 4.2 Definition of OWL DL and OWL Lite Ontologies in RDF Graph Form
• 5. RDF-Compatible Model-Theoretic Semantics (Normative)
  • 5.1 The OWL and RDF Universes
  • 5.2 OWL Interpretations
  • 5.3 OWL Full
  • 5.4 OWL DL
• Appendix A. Proofs (Informative)
  • A.1 Correspondence between Abstract Syntax and OWL DL
    * A.1.1 Correspondence for Descriptions
    * A.1.2 Correspondence for Directives
    * A.1.3 From RDF Semantics to Direct Semantics
    * A.1.4 From Direct Semantics to RDF Semantics
    * A.1.5 Correspondence Theorem
  • A.2 Correspondence between OWL DL and OWL Full
• Appendix B. Examples (Informative)
  • B.1 Examples of Mapping from Abstract Syntax to RDF Graphs
  • B.2 Examples of Entailments in OWL DL and OWL Full
• Appendix C. Changes since Last Call (Informative)
  • C.1 Substantive changes after Last Call
  • C.2 Editorial changes after Last Call
  • C.3 Substantive changes after Candidate Recommendation
  • C.4 Editorial changes after Candidate Recommendation
  • C.5 Changes since Proposed Recommendation
• Index of Vocabulary (Informative)
• Acknowledgments (Informative)
• References
  • Normative References
  • Other References

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 bothOWL 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, calledOWL 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 Semantics] 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 Acontains 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 Aalso 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 particularly interested in Sections3 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. All substantive post-last call changes to the document, as well as some editorial post-last-call changes, are indicated in the style of this appendix.

C.1 Substantive changes after Last Call

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

• [10 April 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0046.html, added owl:Class, owl:Restriction, owl:ObjectProperty, owl:DatatypeProperty, owl:AnnotationProperty, owl:OntologyProperty, owl:Ontology, owl:AllDifferent, owl:FunctionalProperty, owl:InverseFunctionalProperty, owl:SymmetricProperty, and owl:TransitiveProperty to CI in Section 5.2. Some of these were inferrable already.
• [10 April 2003] Related to http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0046.html, added owl:distinctMembers to RI in Section 5.2.
• [15 April 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0064.html, added owl:OntologyProperty to the disallowed vocabulary in disallowed OWL vocabulary in Section 4.2.
• [5 May 2003] Per a decision of the Web Ontology working group on 1 May 2003 to add owl:Nothing to OWL Lite, recorded in http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0017.html, changed the introduction of owl:Nothing to so indicate. The index forowl:Nothing was also updated.
• [9 May 2003] To improve internal consistency, added optional rdf:Property types for Annotation Properties in Section 4.1.
• [30 May 2003] Per a decision of the Web Ontology working group on 29 May 2003 to modify the mapping of EquivalentClasses, recorded in http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0402.html and in response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0003.html and http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0052.html, changed the mapping rule for EquivalentClasses(d1 ... dn) to T(di) owl:equivalentTo T(dj) . for all <i,j> in G where G is a set of pairs over {1,...,n} that if interpreted as an undirected graph forms a connected graph for {1,...,n}.
• [30 May 2003] Per a decision of the Web Ontology working group on 29 May 2003 to add axioms for ontology properties, recorded in http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0402.html, added axioms for ontology properties to the OWL Lite and OWL DL abstract syntax in Sections 2.3.1.3. and Section 2.3.2.4; added direct semantics conditions for ontology property axioms in Section 3.3; and added a mapping for ontology property axioms in Section 4.1. Fixed the proofs of Lemma 2 and Lemma 3.
• [30 May 2003] Per a decision of the Web Ontology working group on 29 May 2003 to change the semantics for owl:intersectionOf and related resources from an intensional semantics to an extensional semantics, recorded in http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0402.html, modified the semantic conditions for owl:intersectionOf,owl:unionOf,owl:complementOf, and owl:oneOf in Section 5.2. No change needed to be made to the proof of Lemma 1. Fixed the proofs of Lemma 4 andLemma 2.
• [2 June 2003] In response to an observation by Jeremy Carroll in http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0004.html, changed the mapping rule for anonymous individuals with no types slightly in Section 4.1.
• [4 June 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0011.html, the treatment of datatypes and rdfs:Literal has been slightly changed in Section 2.3.1.3,Section 2.3.2.3, andSection 4.1.
• [4 June 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0050.html, point owlsas-rdf-equivalent-class, modified the treatment of ontology annotations in Section 3.4.
• [5 June 2003] In response to a comment by Jeremy Carroll in http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0004.html, the direct semantics has been modified to allow for domain elements that are not OWL individuals. These domain elements are used to provide meaning for annotations on classes, properties, and ontologies. Changes have been made in Section 3.1,Section 3.2,Section 3.3, and Appendix A.1.
• [6 June 2003] Changed the treatment of datatypes to correspond with the substantive post-last-call fixes and changes to the treatment of datatypes in RDF. Changes have been made in Section 3.1 andAppendix A.1.
• [26 June 2003] Per a decision of the Web Ontology working group on 26 June 2003 to replace owl:sameIndividualAs with owl:sameAs, recorded in http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0364.html, made changes toSection 2.2,Section 3.3,Section 4.1,Section 4.2,Section 5.2, andAppendix A.1.
• [30 June 2003] Fixed a bug in the semantic conditions for owl:hasValue noticed by Jeremy Carroll, changing the conditions for the value from a property to an individual or a data value in Section 5.2.
• [23 July 2003] In response to a substantive post-last-call change to the RDF semantics, changing the if-and-only-if conditions for rdfs:subClassOf and rdfs:subPropertyOf to only-if conditions, added if-and-only-if conditions for rdfs:subClassOf, over OWL classes, andrdfs:subPropertyOf, over OWL individual-valued properties and over OWL datatype properties, to Section 5.2.
• [23 July 2003] In response to a substantive change to the RDF syntax mapping to triples, removing the typing triples for collections, [applicable document unknown], made typing of list resources optional in Section 4.1. Also modified an example in Appendix B.1.

C.2 Editorial changes after Last Call

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

• [9 April 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0023.html, point 2, changed ``most information about properties'' to ``most information concerning properties'' in Section 2.3.
• [14 April 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0029.html, point 1, added ``Because there is no standard way to go from a URI reference to an XML Schema datatype in an XML Schema, there is no standard way to use user-defined XML Schema datatypes in OWL.'' to the discussion of allowable XML Schema datatypes inSection 2.
• [14 April 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0029.html, point 2.1, added ``(The property rdf:type is added to the annotation properties so as to provide a meaning for deprecation, see below.)'' after ``ER provides meaning for URI references that are used as OWL properties.'' in Section 3.1.
• [14 April 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0029.html, point 2.3, added ``A datatype theory must contain datatypes forxsd:string and xsd:integer. It may contain datatypes for the otherbuilt-in XML Schema datatypes that are suitable for use in OWL. It may also contain other datatypes, but there is no provision in the OWL syntax for conveying what these datatypes are.'' just after the definition of a datatype theory in Section 3.1.
• [14 April 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0029.html, point 2.5, added ``annotations'' the the list of things that EC is extended to in Section 3.2.
• [9 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0050.html, point owlsas-rdf-datatype-denotation, removed the phrase ``as in RDF'' from Section 2.1.
• [9 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0050.html, point owlsas-rdf-equivalent-class, added an explanation of why one might admit EquivalentClasses with only one description in Section 2.3.2.1.
• [9 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0050.html, added ``, for n>=1 '' in the semantic condition for multi-restrictions inSection 3.2.
• [9 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0050.html, changed to ``include class identifiers and restrictions'' in Section 2.3.2.2 and ``Elements of the OWL vocabulary that construct descriptions'' in Section 5.2.
• [13 May 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0180.html, the links in the table of contents for in Appendix A were fixed.
• [14 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0030.html, added a new paragraph to the beginning ofSection 4.
• [14 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0057.html, made some changes to the wording on OWL ontologies in the abstract syntax near the beginning of Section 2.1.
• [14 May 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0057.html, added anchors to the transformations inSection 4.1.
• [14 May 2003] In response to some discussion about ontology names changed the discussion of the purpose of ontology names in Section 2.1.
• [22 May 2003] In response to a message from Jeff Heflin, http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0302.html, added a comment to the effect tools should determine entailment between imports closures in Section 5.3 and Section 5.4. (Removed on 27 May 2003.)
• [22 May 2003] Changed ``consistent with the Web'' to ``imports closed''Section 5.3 and Appendix A.
• [26 May 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0335.html, changed several `if' to `iff' in definitions in Section 3.4,Section 5.3, and Section 5.4. This is editorial as complete definitions are often written using `if'.
• [30 May 2003] Fixed a typographical error in the proof of Lemma 4.
• [4 June 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0029.html, points 2.2 and 2.3, the status ofrdfs:Literal and rdf:XMLLiteral has been clarified inSection 2,Section 2.1, andSection 4.2.
• [19 June 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0257.html, changed to note after the proof of Theorem 2 in Appendix A.2 to note that the converse of the theorem is not true.
• [19 June 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0055.html, changed some explanatory text concerning the transformation to triples in Section 4.1.
• [19 June 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Jun/0264.html, added introductory material about the other WebOnt documents to Section 1.
• [24 June 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0069.html, added note about correspondence to existing DLs to Section 2.
• [22 July 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Jul/0011.html and http://lists.w3.org/Archives/Public/public-webont-comments/2003Jul/0041.html, changed several uses of ``object'' to ``individual'' or ``individual-valued'' in Section 2 andSection 5.2 and made other editorial changes to Section 5.2.
• [23 July 2003] To remove any reference to tools, made wording changes inSection 3.1 and Section 2.1, concerning the treatment of datatypes.
• [25 July 2003] In response to http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0064.html, added explicit tagging of the informative or normative nature of all sections.
• [25 July 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Jul/0296.html, removed a comment about the relationship between the two model theories fromSection 1.
• [6 August 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Jul/0015.html, changed owl:IndividualProperty to owl:ObjectProperty inAppendix A.2.
• [6 August 2003] In response to Section 2.1, concerning the treatment http://lists.w3.org/Archives/Public/public-webont-comments/2003Apr/0064.html, added quotes around rdfs:Literal to indicate that it is a terminal, not a non-terminal, in Section 2.3.1.3 andSection 2.3.2.3.

C.3 Substantive changes after Candidate Recommendation

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

• [18 September 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Sep/0156.html, made the type triples for the individualvaluedPropertyID production inSection 4.1 optional if typing triples would be produced from some other production.
• [3 October 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Sep/0177.html, augmented the mapping from the abstract syntax to triples to allow for collections of axioms and facts outside of ontologies to generate OWL DL in triples made the type triple for anonymous ontologies optional unless the ontology has annotations. Upgraded the definition of entailment in the direct model theory to allow entailment to work over collections of axioms and facts outside of ontologies. Changes were made in Section 3.4,Section 4.2, andSection 5.4. Many of the proofs in Appendix A required minor changes.
• [6 November 2003] In response to proposal http://lists.w3.org/Archives/Public/www-webont-wg/2003Oct/0167.html and in accordance with a decision of the working group http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0000.html, added the condition that EC(owl:Thing) must be nonempty in Section 3.1 and that IOT must be nonempty in Section 5.2.
• [29 November 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0064.htmland http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0132.html, made changes to Section 5.2 to bring the treatment of datatypes into line with the latest version of the RDF semantics [RDF Semantics].
• [29 November 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0064.html, added a note to the beginning of Section 5 (and a reference to this note in Section 5.4) explicitly stating that the Direct Model-Theoretic Semantics takes precedence over the OWL DL semantics.

C.4 Editorial changes after Candidate Recommendation

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

• [29 November 2003] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0132.html, made several editorial changes to Sections 2, 3, 4 and 5.
• [3 December 2003] In further response to http://lists.w3.org/Archives/Public/www-webont-wg/2003Nov/0132.htmland ensuing discussion, made several editorial changes to Sections 3 and5 and Appendix A.

C.5 Changes since Proposed Recommendation

This section provides information on post Proposed Recommendation changes to the document.

• [21 December 2003] Fixed typographical error: Recommentation → Recommendation (in several places).
• [29 January 2004] In response to http://lists.w3.org/Archives/Public/www-webont-wg/2004Jan/0021.html, clarified the definition of separated vocabulary in Section 4.2.
• [29 January 2004] In response to http://www.ilrt.bris.ac.uk/discovery/chatlogs/webont/2004-01-29#T17-08-44, made explicit in the definition of an RDF compatible OWL interpretation in Section 5.2 that an RDF compatible datatype map necessarily includes a datatype for rdf:XMLLiteral.

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 elementSection 4. The fifth column points to the vocabularly element's major definition in the RDFS-compatible semantics of Section 5.

Vocabulary Terms

Acknowledgments

The Joint US/EU ad hoc Agent Markup Language Committeedeveloped DAML+OIL, which is the direct precursor to OWL. Many of the ideas in DAML+OIL and thus in OWL are also present in theOntology Inference Layer (OIL).

This document is the result of extensive discussions within theWeb Ontology Working Groupas a whole. The participants in this working group included: Yasser alSafadi, Jean-François 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, Jérôme 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, Rüdiger 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.

References

Normative References

[RDF Concepts]

Resource Description Framework (RDF): Concepts and Abstract Syntax, Graham Klyne and Jeremy J. Carroll, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/ . Latest version available at http://www.w3.org/TR/rdf-concepts/ .

[RDF Semantics]

RDF Semantics, Patrick Hayes, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ . Latest version available at http://www.w3.org/TR/rdf-mt/ .

[RDF Syntax]

RDF/XML Syntax Specification (Revised), Dave Beckett, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ . Latest versionavailable at http://www.w3.org/TR/rdf-syntax-grammar/ .

[RDF Tests]

RDF Test Cases, Jan Grant and Dave Beckett, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/ . Latest versionavailable at http://www.w3.org/TR/rdf-testcases/ .

[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 2001. 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, Chris Welty, and Deborah L. McGuinness, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-owl-guide-20040210/ . Latest version 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, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-owl-features-20040210/ . Latest version available at http://www.w3.org/TR/owl-features/ .

[OWL Reference]

OWL Web Ontology Language Reference, Mike Dean and Guus Schreiber, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-owl-ref-20040210/ . Latest version available at http://www.w3.org/TR/owl-ref/ .

[RDF Syntax]

RDF/XML Syntax Specification (Revised), Dave Beckett, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ . Latest versionavailable at http://www.w3.org/TR/rdf-syntax-grammar/ .

[RDF Vocabulary]

RDF Vocabulary Description Language 1.0: RDF Schema, Dan Brickley and R. V. Guha, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-schema-20040210/ . Latest version available at http://www.w3.org/TR/rdf-schema/ .