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Web Ontology Language (OWL) Candidate Recommendations

World Wide Web Consortium Issues Web Ontology Language Candidate Recommendations

Emerging Ontology Standard, OWL, Strengthens Semantic Web Foundations

W3C ( 19-August-2003.

Today, the World Wide Web Consortium (W3C) issued Web Ontology Language (OWL) as a W3C Candidate Recommendation. Candidate Recommendation is an explicit call for implementations, indicating that the document has been reviewed by all other W3C Working Groups, that the specification is stable, and appropriate for implementation.

OWL is a language for defining structured, Web-based ontologies which enable richer integration and interoperability of data across application boundaries. Early adopters of these standards include bioinformatics and medical communities, corporate enterprise and governments. OWL enables a range of descriptive applications including managing web portals, collections management, content-based searches, enabling intelligent agents, web services and ubiquitous computing.

"OWL is an important step for making data on the Web more machine processable and reusable across applications, " said Tim Berners-Lee, W3C Director. "We're encouraged to see OWL already being used as an open standard for deploying large scale ontologies on the Web."

OWL is specified in 6 documents: The OWL Overview; OWL Semantics and Abstract Syntax; OWL Use Cases and Requirements; OWL Test Cases, OWL Guide, and the OWL Reference.

Read the FAQ for more details on OWL.

OWL Delivers Ontologies that Work on the Web

OWL is a Web Ontology language. Where earlier languages have been used to develop tools and ontologies for specific user communities (particularly in the sciences and in company-specific e-commerce applications), they were not defined to be compatible with the architecture of the World Wide Web in general, and the Semantic Web in particular.

OWL rectifies this by using both URIs for naming and the linking provided by RDF to add the following capabilities to ontologies:

  • Ability to be distributed across many systems
  • Scalable to Web needs
  • Compatible with Web standards for accessibility and internationalization
  • Open and extensible

OWL provides a language for defining structured, Web-based ontologies which delivers richer integration and interoperability of data among descriptive communities.

OWL builds on RDF Model and Schema and adds more vocabulary for describing properties and classes: among others, relations between classes (e.g., disjointness), cardinality (e.g., "exactly one"), equality, richer typing of properties, characteristics of properties (e.g., symmetry), and enumerated classes.

Already there are multiple implementations and demonstrations of OWL, which are available to the public.

The OWL Documents Produced by W3C

The W3C Web Ontology Working Group has produced six OWL documents. Each is aimed at different segments of those wishing to learn, use, implement or understand the OWL language. Documents include:

  • A presentation of the use cases and requirements that motivated OWL
  • An overview document which briefly explains the features of OWL and how they can be used
  • A comprehensive Guide that walks through the features of OWL with many examples of the use of OWL features
  • A reference document that provides the details of every OWL feature
  • A test case document, and test suite, providing over a hundred tests that can be used for making sure that OWL implementations are consistent with the language design
  • A document presenting the semantics of OWL and details of the mapping from OWL to RDF

The Candidate Recommendation phase for the OWL documents is estimated to last at least four weeks, at which time the Working Group will evaluate new implementations and comments on the drafts.

OWL's Place in the Architecture of the Semantic Web: XML, RDF, and Ontologies

Much has been written about the Semantic Web, as if it is a replacement technology for the Web we know today. In fact, the Semantic Web is made through incremental changes, by bringing machine-readable descriptions to the data and documents already on the Web. With both descriptions and ways to connect, compare, and contrast them, it's possible to build applications, tools, search engines, agents - all with no apparent change to Web pages.

W3C's Semantic Web Activity builds on work done in other W3C Activities, such as the XML Activity. Its focus is to develop standard technologies, on top of XML, that support the growth of the Semantic Web.

At the foundation, XML provides a set of rules for creating vocabularies that can bring structure to both documents and data on the Web. XML gives clear rules for syntax; XML Schemas then serve as a method for composing XML vocabularies. XML is a powerful, flexible surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents.

RDF -- the Resource Description Framework -- is a standard a way for simple descriptions to be made. What XML is for syntax, RDF is for semantics -- a clear set of rules for providing simple descriptive information. RDF Schema then provides a way for those descriptions to be combined into a single vocabulary. What's needed next is a way to develop subject- or domain-specific vocabularies. That is the role of an ontology.

An ontology defines the terms used to describe and represent an area of knowledge. Ontologies are used by people, databases, and applications that need to share subject-specific (domain) information -- like medicine, tool manufacturing, real estate, automobile repair, financial management, etc. Ontologies include computer-usable definitions of basic concepts in the domain and the relationships among them. They encode knowledge in a domain and also knowledge that spans domains. In this way, they make that knowledge reusable.

Industrial and Academic Leaders Move OWL Forward

The W3C Web Ontology Working Group carries a complement of industrial and academic expertise, lending the depth of research and product implementation experience necessary for building a robust ontology language system. Participants include representatives from Agfa-Gevaert N. V; Daimler Chrysler Research and Technology; DARPA; Defense Information Systems Agency (DISA); EDS; Fujitsu; Forschungszentrum Informatik (FZI); Hewlett Packard Company; Ibrow; IBM; INRIA; Ivis Group; Lucent; University of Maryland; Mondeca; Motorola; National Institute of of Standards and Technology (NIST); Network Inference, Nokia; Philips, University of Southampton; Stanford University; Sun Microsystems; Unicorn Solutions along with invited experts from German Research Center for Artificial Intelligence (DFKI) Gmbh; the Interoperability Technology Association for Information Processing, Japan (INTAP); and the University of West Florida.

OWL brings together research from a number of groups that have been developing languages in which to express ontological expressions on the web. OWL has its origins in two major research efforts: a draft language known as the DARPA Agent Markup Language Ontology notations (DAML-ONT) and Ontology Interface Layer (OIL) developed by European researchers with the support of the European Commission. Since then, an ad hoc group of researchers formed the Joint US/EU committee on Agent Markup Languages and released a new version of this language which merges DAML with the OIL. The documents released today reflect the collaborative work of international researchers with industrial participants working together the World Wide Web Consortium.

About the World Wide Web Consortium (W3C)

The W3C was created to lead the Web to its full potential by developing common protocols that promote its evolution and ensure its interoperability. It is an international industry consortium jointly run by the MIT Laboratory for Computer Science (MIT LCS) in the USA, the European Research Consortium for Informatics and Mathematics (ERCIM) headquartered in France and Keio University in Japan. Services provided by the Consortium include: a repository of information about the World Wide Web for developers and users, and various prototype and sample applications to demonstrate use of new technology. To date, nearly 400 organizations are Members of the Consortium. For more information see


Janet Daly
Tel: +1.617.253.5884
Tel: +1.617.253.2613


Prepared by Robin Cover for The XML Cover Pages archive. See additional references in the news story "W3C Releases Candidate Recommendations for Web Ontology Language (OWL)." General references in "OWL Web Ontology Language."

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