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243 lines
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<title>Frequently Asked Questions on W3C's Web Ontology Language (OWL)</title>
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<h1>Frequently Asked Questions on W3C's Web Ontology Language (OWL)</h1>
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<p><em>Status: this FAQ is no longer maintained. For a new, up-to-date FAQ, see
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the <a href="http://www.w3.org/2001/sw/SW-FAQ">Semantic Web FAQ</a>.</em></p>
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<h2>Q. What is an ontology?</h2>
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<p>A. Although the concept of ontology has been around for a very long time in
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philosophy, in recent years it has become identified with computers as a
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machine readable vocabulary that is specified with enough precision to allow
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differing terms to be precisely related.</p>
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<p>More precisely, from the <a
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href="http://www.w3.org/TR/2004/REC-webont-req-20040210/">OWL Requirements
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Document</a>:</p>
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<blockquote>
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An ontology defines the terms used to describe and represent an area of
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knowledge. Ontologies are used by people, databases, and applications that
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need to share domain information (a domain is just a specific subject area or
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area of knowledge, like medicine, tool manufacturing, real estate, automobile
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repair, financial management, etc.). Ontologies include computer-usable
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definitions of basic concepts in the domain and the relationships among them
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[...]. They encode knowledge in a domain and also knowledge that spans
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domains. In this way, they make that knowledge reusable.</blockquote>
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<p></p>
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<h2>Q. How is OWL different from earlier ontology languages?</h2>
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<p>A. OWL is a <em>Web</em> Ontology language. Where earlier languages have
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been used to develop tools and ontologies for specific user communities
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(particularly in the sciences and in company-specific e-commerce applications),
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they were not defined to be compatible with the architecture of the World Wide
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Web in general, and the Semantic Web in particular.</p>
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<p>OWL rectifies this by providing a language which uses the linking provided
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by <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">RDF</a> to add
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the following capabilities to ontologies:</p>
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<ul>
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<li>Ability to be distributed across many systems</li>
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<li>Scalable to Web needs</li>
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<li>Compatible with Web standards for accessibility and
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internationalization.</li>
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<li>Open and extensible</li>
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</ul>
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<p></p>
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<h2>Q. What can Web Ontologies be used for?</h2>
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<p>A. The Web Ontology Working Group identified major use cases of ontologies
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on the Web and described these in <a
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href="http://www.w3.org/TR/2004/REC-webont-req-20040210/">the Use Cases and
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Requirements document</a>. A survey of implemented applications (using earlier
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web ontology languages) was made with about 25 actually deployed systems
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identified.</p>
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<p>The WG categorized these into six main areas, as follows:</p>
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<p></p>
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<ul>
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<li>Web Portals
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<ul>
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<li>Categorization rules used to enhance search</li>
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</ul>
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</li>
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<li>Multimedia Collections
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<ul>
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<li>Content-based searches for non-text media</li>
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</ul>
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</li>
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<li>Corporate Web Site Management
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<ul>
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<li>Automated Taxonomical Organization of data and documents</li>
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<li>Mapping Between Corporate Sectors (mergers!)</li>
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</ul>
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</li>
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<li>Design Documentation
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<ul>
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<li>Explication of "derived" assemblies (e.g. the wing span of an
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aircraft)</li>
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<li>Explicit Management of Constraints</li>
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</ul>
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</li>
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<li>Intelligent Agents
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<ul>
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<li>Expressing User Preferences and/or Interests</li>
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<li>Content Mapping between Web sites</li>
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</ul>
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</li>
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<li>Web Services and Ubiquitous Computing
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<ul>
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<li>Web Service Discovery and Composition</li>
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<li>Rights Management and Access Control</li>
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</ul>
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</li>
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</ul>
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<p></p>
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<h2>Q. Who is implementing OWL tools and applications?</h2>
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<p>A. A large number of organizations have been exploring the use of OWL, with
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many tools currently available. The Working Group is maintaining a <a
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href="http://www.w3.org/2001/sw/WebOnt/impls">list of implementations and
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demonstrations</a>. In addition, both the US government (via DARPA and NSF) and
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the European Union (via the 5th and 6th generation frameworks of the IST
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program) have invested in web ontology language development. Most of the
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systems currently using DAML, OIL and <a href="http://www.daml.org">DAML+OIL
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</a> (the predecessor languages that OWL was based on) are now migrating to
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OWL. In addition, a number of ontology language tools, such as the widely used
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<a href="http://protege.stanford.edu/plugins/owl/">Protege system</a>, now
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provide OWL support.</p>
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<p></p>
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<h2>Q. Are there OWL ontologies available already?</h2>
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<p>A. There are a large number of ontologies available on the Web in OWL. There
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is an ontology library at <a href="http://www.daml.org/ontologies/">DAML
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ontology library</a>, which contains about 250 examples written in OWL or
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DAML+OIL (a <a href="http://www.mindswap.org/2002/owl.html">converter from
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DAML+OIL to OWL</a> is available on the web). In addition, several large
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ontologies have been released in OWL. These include <a
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href="http://www.mindswap.org/2003/CancerOntology/">a cancer ontology in
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OWL</a> developed by the US National Cancer Institute's <a
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href="http://ncicb.nci.nih.gov/">Center for Bioinformatics,</a> which contains
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about 17,000 cancer related terms and their definitions, and an OWL version of
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the well-known <a href="http://www.opengalen.org/index.html">GALEN medical
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ontology</a>, developed at the University of Manchester.</p>
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<p></p>
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<h2>Q. What does OWL add that RDF-schema doesn't?</h2>
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<p>A. Owl extends RDFS to allow for the expression of complex relationships
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between different RDFS classes and of more precise constraints on specific
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classes and properties. Example of these include: - the means to limit the
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properties of classes with respect to number and type, - the means to infer
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that items with various properties are members of a particular class - the
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means to determine if all members of a class will have a particular property,
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or if only some of them might - the means to distinguish one-to-one from
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many-to-one or one-to-many relationships, allowing the "foreign keys" of a
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database to be represented in an ontology - the means to express relationships
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between classes defined in different documents across the web, - the means to
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construct new classes out of the unions, intersections and complements of other
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classes, and - the means to constrain range and domain to specific
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class/property combinations. The <a
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href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/">OWL Guide</a> provides
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examples of all of these in the area of describing food and wine.</p>
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<p></p>
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<h2>Q. What documents are in the OWL document set?</h2>
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<p>A. The Working Group has produced six documents each aimed at different
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segments of those wishing to learn, use, implement or understand the OWL
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language. Our documents include - a presentation of the <a
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href="http://www.w3.org/TR/2004/REC-webont-req-20040210/">use cases and
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requirements </a> that motivated OWL - an <a
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href="http://www.w3.org/TR/2004/REC-owl-features-20040210/">overview</a>
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document which briefly explains the features of OWL and how they can be used -
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a comprehensive <a
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href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/">Guide</a> that
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provides a walk-through of the features of OWL with many examples of the use of
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OWL features - a <a
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href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/">reference document</a>
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that provides the details of every OWL feature - a <a
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href="http://www.w3.org/TR/2004/REC-owl-test-20040210/">test case document</a>,
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and <a href="http://www.w3.org/2002/03owlt/">test suite</a>, providing over a
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hundred tests that can be used for making sure that OWL implementations are
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consistent with the language design - a document presenting <a
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href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/">the semantics of
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OWL and details of the mapping from OWL to RDF</a> (This document presents the
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model theoretical details of every feature of OWL so that those implementing
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complete OWL reasoners can guarantee algorithmic compliance with all aspects of
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the language design).</p>
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<h2>Q. What is new about ontologies on the Semantic Web? How do they differ
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from expert systems and the other artificial intelligence (AI) technologies
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promoted in the 1980s?</h2>
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<p>A. The relation between the Semantic Web, and OWL in particular, to work in
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AI is somewhat parallel to the relation between the Web and the hypertext
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community -- based on some of the same motivations, but with a very different
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architecture that drastically changes the ways in which the technology can be
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deployed. In a <a
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href="http://www.sciam.com/article.cfm?articleID=00048144-10D2-1C70-84A9809EC588EF21">widely
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cited article</a> from <em>Scientific American</em>, Berners-Lee, Hendler and
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Lassila wrote:</p>
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<blockquote>
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For the semantic web to function, computers must have access to structured
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collections of information and sets of inference rules that they can use to
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conduct automated reasoning. Artificial-intelligence researchers have studied
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such systems since long before the Web was developed. Knowledge
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representation, as this technology is often called, is currently in a state
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comparable to that of hypertext before the advent of the Web: it is clearly a
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good idea, and some very nice demonstrations exist, but it has not yet
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changed the world. It contains the seeds of important applications, but to
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realize its full potential it must be linked into a single global system.
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</blockquote>
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<p>The OWL language is a major step towards developing that potential.</p>
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<h2>Q. What does the acronym "OWL" stand for?</h2>
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<p>A. Actually, OWL is not a real acronym. The language started out as the "Web
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Ontology Language" but the Working Group disliked the acronym "WOL." We decided
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to call it OWL. The Working Group became more comfortable with this decision
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when one of the members pointed out the following justification for this
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decision from the noted ontologist A.A. Milne who, in his influential book
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"Winnie the Pooh" stated of the wise character OWL:</p>
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<p>"He could spell his own name WOL, and he could spell Tuesday so that you
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knew it wasn't Wednesday..."</p>
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<address>
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Jim Hendler, co-chair of the <a href="http://www.w3.org/2001/sw/WebOnt/">W3C
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Web Ontology Working Group</a>, and the <a href="mailto:w3t-pr@w3.org">W3C
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Communications Team</a><br />
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$Date: 2008/05/21 20:54:18 $
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</address>
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<p></p>
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<p></p>
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</body>
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