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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 model theory 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.
This is a W3C Web Ontology Working Group Working Draft produced 3 February 2003 as part of the W3C Semantic Web Activity (Activity Statement). It incorporates decisions made by the Working Group in designing the OWL Web Ontology Language. This is a public W3C Working Draft and may be updated, replaced, or obsoleted by other documents at any time. However, it is expected that this working draft is quite close to the Last Call version of the document. It is inappropriate to use W3C Working Drafts as reference material or to cite as other than "work in progress". A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR/.
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This document contains several interrelated 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 model-theoretic 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. For such OWL ontologies the direct model theory is authoritative and the RDFS-compatible model theory is secondary. 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.
The language described in this document is very close to the DAML+OIL web ontology language [DAML+OIL]. The only substantive changes between OWL and DAML+OIL are
There are also a number of minor differences between OWL and DAML+OIL, including a number of changes to the names of the various constructs, as mentioned in Appendix A of the OWL Reference Description [OWL Reference].
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 DAM+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.
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 Term||Abstract OWL DL Syntax||Abstract OWL Lite Syntax||Direct Semantics||Mapping to Triples||RDFS-Compatible Semantics|