The W3C Web Ontology Working Group has produced a Version 1.0 working draft document Web Ontology Language (OWL) Guide documenting key concepts and uses of the OWL language. Building upon the foundations of the DAML+OIL specification, the W3C Web Ontology Language (OWL) "is intended to provide a language that can be used to describe the classes and relations between them that are inherent in Web documents and applications. The new Guide demonstrates the use of the OWL language (1) to formalize a domain by defining classes and properties of those classes, (2) to define individuals and assert properties about them, and (3) to reason about these classes and individuals to the degree permitted by the formal semantics of the OWL language. Document sections are organized to present an incremental definition of a set of classes, properties and individuals, beginning with the fundamentals and proceeding to more complex language components." The development of the Web Ontology Language is motivated by a recognition that the World Wide Web "as it is currently constituted resembles a poorly mapped geography. Our insight into the documents and capabilities available are based on keyword searches, abetted by clever use of document connectivity and usage patterns. The sheer mass of this data is unmanageable without powerful tool support. In order to map this terrain more precisely, computational agents require machine-readable descriptions of the content and capabilities of web accessible resources. These descriptions must be in addition to the human-readable versions of that information."

Bibliographic information: Web Ontology Language (OWL) Guide Version 1.0. W3C Working Draft 4-November-2002. Version URL: http://www.w3.org/TR/2002/WD-owl-guide-20021104/. Latest version URL: http://www.w3.org/TR/owl-guide/. By Michael K. Smith (Electronic Data Systems), Deborah McGuinness (Stanford University), Raphael Volz (Forschungszentrum Informatik - FZI), and Chris Welty (IBM Research). "This document represents the work of many people, in particular the members of the W3C Web Ontology Working Group. Appendix B was contributed by Guus Schreiber, University of Amsterdam. Substantial insight was provided by the DAML+OIL Walkthru. Jeremy Carroll, Jeff Heflin, Leo Obrst, and Peter F. Patel-Schneider provided helpful reviews. At the WG Face to Face, October 8, 2002, Stephen Buswell, Ruediger Klein, Enrico Motta, and Evan Wallace provided a detailed review of the ontology resulting in substantial changes."

From the WD Introduction:

To support [intelligent computation in Web applications], it is necessary to go beyond keywords and specify the meaning of the resources described on the web. This additional layer of interpretation captures the semantics of the data.

OWL is a language for defining Web ontologies and their associated knowledge bases. Ontology is a term borrowed from philosophy that refers to the science of describing the kinds of entities in the world and how they are related. In OWL, an ontology is a set of definitions of classes and properties, and constraints on the way those classes and properties can be employed. An OWL ontology may include the following elements:

• taxonomic relations between classes
• datatype properties, descriptions of attributes of elements of classes
• object properties, descriptions of relations between elements of classes

and, to a lesser degree

• instances of classes and
• instances of properties

Datatype properties and object properties are collectively the properties of a class...

Species of OWL. "OWL is in fact a set of three, increasingly complex languages:

Owl Lite has been defined with the intention of creating a simple language that will satisfy users primarily needing a classification hierarchy and simple constraint features. For example, while it supports cardinality constraints, it only permits cardinality values of 0 or 1. For these reasons, it should be simpler to provide tool support for Owl Lite than its more complex relatives.

OWL DL includes the complete OWL vocabulary, interpreted under a number of simple constraints. Primary among these is type separation. Class identifiers cannot simultaneously be properties or individuals. Similarly, properties cannot be individuals. OWL DL is so named due to its correspondence with description logics.

OWL Full includes the complete OWL vocabulary, interpreted more broadly than in OWL DL, with the freedom provided by RDF. In OWL Full a class can be treated simultaneously as a collection of individuals (the class extension) and as an individual in its own right (the class intension). Another significant difference from OWL DL is that a DatatypeProperty can be marked as an InverseFunctionalProperty. These are differences that will be of interest to the advanced user.