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WEB ONTOLOGY LANGUAGE

Web Ontology Language (OWL) is a markup language for publishing and sharing data using ontologies on the Internet. OWL is a vocabulary extension of the Resource Description Framework (RDF) and is derived from the DAML+OIL Web Ontology Language (see also DAML and OIL). Together with RDF and other components, these tools make up the Semantic Web project.

OWL represents the meanings of terms in vocabularies and the relationships between those terms in a way that is suitable for processing by software.

The OWL specification is maintained by the World Wide Web Consortium (W3C).

OWL is seen as a major technology for the future implementation of a Semantic Web. OWL was designed specifically to provide a common way to process the content of web information. The language is intended to be read by computer applications instead of by humans. And because OWL is written in XML, OWL information can be easily exchanged between different types of computers using different operating systems, and application languages. OWL's main purpose will be to provide standards that provide a framework for asset management, enterprise integration and the sharing and reuse of data on the Web. OWL was developed mainly because it has more facilities for expressing meaning and semantics than XML, RDF, and RDF-S, and thus OWL goes beyond these languages in its ability to represent machine interpretable content on the web. [1]

OWL currently has three flavors: OWL Lite, OWL DL, and OWL Full. These flavors incorporate different features, and in general it is easier to reason about OWL Lite than OWL DL and OWL DL than OWL Full. OWL Lite and OWL DL are constructed in such a way that every statement can be decided in finite time; OWL Full can contain endless 'loops'.

Contents

History

OWL DL is based on the description logic \mathcal{SHOIN} (D). Its subset OWL Lite is based on the less expressive logic \mathcal{SHIF} (D). All reasoning tasks in both OWL DL and OWL Lite can be reduced to knowledge based (KB) satisfiablity. OWL is encoded in RDF/XML documents. [2]

The OWL Language is a revision of the DAML+OIL web ontology language incorporating learnings from the design and application use of DAML+OIL.[3]

The initial effort to identify design goals and requirements was co-led by Deborah McGuinness and the editor. Some of the requirements were directly contributed by Dr. McGuinness based upon over a decade of work in building ontology-based systems. Other requirements were identified as part of the editor's Ph.D. thesis work in building a prototype Semantic Web system. A draft version of the Corporate Web Site Management section was written by Michael Smith. [4]

The W3C Working Group began work on November 1, 2001. The first working drafts of the abstract syntax, reference and synopsis were published in July 2002. The OWL documents became a formal W3C recommendation on February 10, 2004 and the working group was disbanded on May 31, 2004. [5]

Sublanguages

OWL provides three increasingly expressive sublanguages designed for use by specific communities of implementers and users.

  • OWL Lite supports those users primarily needing a classification hierarchy and simple constraints. For example, while it supports cardinality constraints, it only permits cardinality values of 0 or 1. It should be simpler to provide tool support for OWL Lite than its more expressive relatives, and OWL Lite provides a quick migration path for thesauri and other taxonomies. Owl Lite also has a lower formal complexity than OWL DL, see the section on OWL Lite in the OWL Reference for further details.
  • OWL DL supports those users who want the maximum expressiveness while retaining computational completeness (all conclusions are guaranteed to be computed) and decidability (all computations will finish in finite time). OWL DL includes all OWL language constructs, but they can be used only under certain restrictions (for example, while a class may be a subclass of many classes, a class cannot be an instance of another class). OWL DL is so named due to its correspondence with description logic, a field of research that has studied the logics that form the formal foundation of OWL.
  • OWL Full is meant for users who want maximum expressiveness and the syntactic freedom of RDF with no computational guarantees. For example, in OWL Full a class can be treated simultaneously as a collection of individuals and as an individual in its own right. OWL Full allows an ontology to augment the meaning of the pre-defined (RDF or OWL) vocabulary. It is unlikely that any reasoning software will be able to support complete reasoning for every feature of OWL Full.

Each of these sublanguages is an extension of its simpler predecessor, both in what can be legally expressed and in what can be validly concluded. The following set of relations hold. Their inverses do not.

  • Every legal OWL Lite ontology is a legal OWL DL ontology.
  • Every legal OWL DL ontology is a legal OWL Full ontology.
  • Every valid OWL Lite conclusion is a valid OWL DL conclusion.
  • Every valid OWL DL conclusion is a valid OWL Full conclusion.

The acronym

Some may claim that the correct acronym for Web Ontology Language should be WOL instead of OWL. Although the character Owl from Winnie the Pooh wrote his name WOL, the acronym OWL was proposed without reference to that character, as an easily pronounced acronym that would yield good logos, suggest wisdom, and honor William A. Martin's One World Language KR project from the 1970s. And, to quote Guus Schreiber, Why not be inconsistent in at least one aspect of a language which is all about consistency?

See also

External links

Tools

  • FaCT++ GPL reasoner for SHOIQ(D), a language slightly more powerful than OWL DL
  • Pellet Open source reasoner for OWL DL
  • RacerPro the commercial OWL RDF Reasoner
  • KAON2 Closed source inference engine for OWL-DL and DL-safe rules
  • OWL Book Book that describes OWL syntax
  • Protege OWL OWL plugin for the Protégé ontology editor (freeware).
  • SemanticWorks the commercial OWL editor from Altova
  • SWOOP OWL Ontology Editor developed by the Maryland Information and Network Dynamics Lab Semantic Web Agents Project (freeware).
  • Model Futures OWL Editor (Beta) - a simple tool for working with OWL
  • The DERI Ontology Management Environment (DOME)
  • TopBraid Composer the commercial OWL/RDF/SPARQL and SWRL development environment based on Eclipse from TopQuadrant