Semantic Web Programming

Appendix B. The OWL Web Ontology Language

This appendix describes the OWL Web Ontology Language, the language used to build ontologies that describe information on the Semantic Web. OWL and its associated semantics are covered in depth in Chapter 4, "Incorporating Semantics." Appendix A, "RDF," presents the Resource Description Framework, its terse vocabulary of terms, and numerous illustrative examples. Because Chapter 4 already contains a lot of examples, this appendix focuses instead on providing a reference for the OWL vocabulary. The appendix is divided into major sections, each dealing with a different aspect of OWL. Each section contains a list of the OWL vocabulary terms and descriptions relevant to the topic of the section.

OWL extends RDF and RDF Schema (RDFS) to provide a vocabulary of properties and classes that have associated semantics. These classes and properties are used to build expressive ontologies that are in turn used to describe resources. Table B-1 contains the namespaces used by the OWL specification.

OWL requires adherence to two important assumptions:

Open world assumption

—The open world assumption states that the truth of a statement is independent of whether it is known. In other words, not knowing that a statement is explicitly true does not imply that the statement is false.

No unique names assumption

—The no unique names assumption states that unless explicitly stated otherwise, you cannot assume that resources that are identified by different URIs are ...