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<head>
  <title>OWL Web Ontology Language Guide</title>

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<body lang="EN" xml:lang="EN">
  <div class="head">
    <a href="http://www.w3.org/">
      <img height="48" alt="W3C" src="http://www.w3.org/Icons/w3c_home" width="72"  />
    </a> 
    <h1 id="mainTitle">OWL Web Ontology Language<br />
        Guide</h1>
    <h2><a id="w3c-doctype" name="w3c-doctype"></a>
        W3C Recommendation 10 February 2004</h2>

      <div id="owl_2_notice" style="border: solid black 1px; padding: 0.5em; background: #FFB;">

	<p style="margin-top: 0; font-weight: bold;">New Version
        Available: OWL 2 <span style="padding-left: 2em;"></span>
        (Document Status Update, 12 November 2009)</p>

	<p style="margin-bottom: 0;">The OWL Working Group has produced
	a W3C Recommendation for a new version of OWL which adds
	features to this 2004 version, while remaining compatible.
	Please see <a href="http://www.w3.org/TR/owl2-overview">OWL 2
	Document Overview</a> for an introduction to OWL 2 and a guide
	to the OWL 2 document set.</p>

      </div>

	

    <dl>
      <dt>This version: </dt>
      	<dd><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/">
            http://www.w3.org/TR/2004/REC-owl-guide-20040210/
	    </a>
        </dd>
      <dt>Latest version: </dt>
      	<dd><a href="http://www.w3.org/TR/owl-guide/">
            http://www.w3.org/TR/owl-guide/
	    </a>
        </dd>
      <dt>Previous version:</dt>
      	<dd><a href="http://www.w3.org/TR/2003/PR-owl-guide-20031215/">
            http://www.w3.org/TR/2003/PR-owl-guide-20031215/
	    </a>
	</dd>
      <dt>Editors:</dt>
      	<dd>
      	  Michael K. Smith, Electronic Data Systems, 
          <img align="middle" src="Email.Michael.K.Smith.gif"
	       alt="Michael dot Smith at e d s dot com"/> <br />
      	  Chris Welty, IBM Research,
	  <img align="middle" src="Email.Chris.Welty.gif"
	       alt="Chris dot Welty at u s dot ibm dot com"/> <br />
      	  Deborah L. McGuinness, Stanford University, 
          <img align="middle" src="Email.Deborah.McGuinness.gif"
	       alt="d l m at k s l dot stanford dot edu"/> <br />
      	</dd>
   </dl>
   

<p>Please refer to the <a
href="http://www.w3.org/2001/sw/WebOnt/errata#owl-guide"><strong>errata</strong></a>
for this document, which may include some normative corrections.</p>

<p>See also <a href="http://www.w3.org/2001/sw/RDFCore/translation/owl-guide">translations</a>.</p>

<p class="copyright"><a
      href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">
      Copyright</a> &#xa9; 2004 <a
      href="http://www.w3.org/"><acronym
      title="World Wide Web Consortium">W3C</acronym></a><sup>&#xae;</sup>
      (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>,
      <a href="http://www.ercim.org/">
      <acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym>
      </a>, <a href="http://www.keio.ac.jp/">Keio</a>),
      All Rights Reserved. W3C
      <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">
      liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">
      trademark</a>, <a href="http://www.w3.org/Consortium/Legal/copyright-documents">
      document use</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-software">
      software licensing</a> rules apply.</p>

    <hr title="Separator for header" />
  </div>

<h2><a id="Abstract" name="Abstract">Abstract</a></h2> 

<p>
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.
</p>

<p>
The OWL Web Ontology Language 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.  
</p>

<p>
This document demonstrates the use of the OWL language to 
</p>

<ol>
<li>formalize a domain by defining classes and properties of those classes,</li>
<li>define individuals and assert properties about them, and</li>
<li>reason about these classes and individuals to the degree permitted
by the formal semantics of the OWL language.</li>
</ol> 

<p>
The 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.
</p>


<hr />

<h2><a id="Status" name="Status"></a>Status of This Document</h2>
<div class="status">
<!-- Start Status-Of-This-Document Text -->

<p>This document has been reviewed by W3C Members and other interested
parties, and it has been endorsed by the Director as a <a
href="http://www.w3.org/2003/06/Process-20030618/tr.html#RecsW3C">W3C
Recommendation</a>.  W3C's role in making the Recommendation is to
draw attention to the specification and to promote its widespread
deployment. This enhances the functionality and interoperability of
the Web.</p>

<p>This is one of <a
href="http://www.w3.org/TR/2004/REC-owl-features-20040210/#s1.1">six
parts</a> of the W3C Recommendation for OWL, the Web Ontology
Language.  It has been developed by the <a
href="http://www.w3.org/2001/sw/WebOnt/">Web Ontology Working
Group</a> as part of the <a href="http://www.w3.org/2001/sw/">W3C
Semantic Web Activity</a> (<a
href="http://www.w3.org/2001/sw/Activity">Activity Statement</a>, <a
href="http://www.w3.org/2001/sw/WebOnt/charter">Group Charter</a>) for
publication on 10 February 2004.  </p>

<p>The design of OWL expressed in earlier versions of these documents
has been widely reviewed and satisfies the Working Group's <a
href="http://www.w3.org/TR/webont-req/"> technical requirements</a>.
The Working Group has addressed <a
href="http://lists.w3.org/Archives/Public/public-webont-comments/">
all comments received</a>, making changes as necessary.  Changes to
this document since <a
href="http://www.w3.org/TR/2003/PR-owl-guide-20031215/">the Proposed
Recommendation version</a> are detailed in the <a
href="./#changes-since-PR">change log</a>.</p>

<p>Comments are welcome at <a
href="mailto:public-webont-comments@w3.org">public-webont-comments@w3.org</a>
(<a
href="http://lists.w3.org/Archives/Public/public-webont-comments/">archive</a>)
and general discussion of related technology is welcome at <a
href="mailto:www-rdf-logic@w3.org">www-rdf-logic@w3.org</a> (<a
href="http://lists.w3.org/Archives/Public/www-rdf-logic/"
shape="rect">archive</a>).
</p>

<p>A list of <a href="http://www.w3.org/2001/sw/WebOnt/impls">
implementations</a> is available.</p>

<p>The W3C maintains a list of <a
href="http://www.w3.org/2001/sw/WebOnt/discl" rel="disclosure">any
patent disclosures related to this work</a>.
</p>

<p><em>This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p>

<!-- End Status-Of-This-Document Text -->
</div>

<hr />

<!-- tag syntax.  Drop initial 'the', delete all spaces. 
     Truncate at any other punctuation or 'and'. Disambiguate with 1, 2, ... -->

<h1><a id="Contents" name="Contents">Contents</a></h1>

<ul>
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Abstract">Abstract</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Status">Status of This Document</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Contents">Contents</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Introduction">1. Introduction</a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OwlVarieties">1.1. The Species of OWL</a></li>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#StructureOfDoc">1.2. Structure of the Document</a></li> 
    </ul></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#StructureOfOntologies">2. The Structure of Ontologies</a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Namespaces">2.1. Namespaces </a></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyHeaders">2.2. Ontology Headers</a></li>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Privacy">2.3. Data Aggregation and Privacy</a></li>
    </ul></li>
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#BasicDefinitions">3. Basic Elements</a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#SimpleClasses">3.1. Simple Classes and Individuals</a>
      	<ul>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningSimpleClasses">3.1.1. Simple Named Classes </a></li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningIndividuals">3.1.2. Individuals </a></li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DesignForUse">3.1.3. Design for Use</a></li>
      	</ul></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#SimpleProperties">3.2. Simple Properties </a>
      	<ul>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningProperties">3.2.1. Defining Properties </a> </li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Datatypes1">3.2.2. Properties and Datatypes</a></li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#PropertiesOfIndividuals">3.2.3. Properties of Individuals</a></li>
      	</ul></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#PropertyCharacteristics">3.3. Property Characteristics</a>
      	<ul>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#TransitiveProperty">3.3.1. TransitiveProperty</a></li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#SymmetricProperty">3.3.2. SymmetricProperty</a></li> 
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#FunctionalProperty">3.3.3. FunctionalProperty</a></li> 
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#inverseOf">3.3.4. inverseOf</a></li> 
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#InverseFunctionalProperty">3.3.5. InverseFunctionalProperty</a></li> 
      	</ul></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#PropertyRestrictions">3.4. Property Restrictions</a>
      	<ul>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#allValuesFrom">3.4.1. allValuesFrom, someValuesFrom </a></li>
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#simpleCardinality">3.4.2. Cardinality </a></li> 
      	  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#hasValue">3.4.3. hasValue</a></li> 
      	</ul></li> 
    </ul></li>  
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyMapping">4. Ontology Mapping </a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#equivalentClass1">4.1. Equivalence between Classes and Properties</a></li>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#sameAs">4.2. Identity between Individuals</a></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#differentFrom">4.3. Different Individuals</a></li> 
    </ul></li>  
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#ComplexClasses">5. Complex Classes</a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#SetOperators">5.1. Set Operators</a></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#EnumeratedClasses">5.2. Enumerated Classes</a></li> 
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DisjointClasses">5.3. Disjoint Classes</a></li>
    </ul>
  </li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyVersioning">6. Ontology Versioning</a></li>

  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Usage">7. Usage Examples</a>
    <ul>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#WinePortal">7.1. Wine Portal</a></li>
      <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#WineAgent">7.2. Wine Agent</a></li>
    </ul>
  </li>
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Acknowledgements">Acknowledgements</a></li>
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWLGlossary">OWL Glossary</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#TermIndex">Term Index and Cross Reference</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#References">References</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#AppendixA">Appendix A: XML + RDF Basics</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#AppendixB">Appendix B: History</a></li> 
  <li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#changes-since-PR">Appendix C: Change Log Since Last Call Release</a></li> 
</ul>

<hr />

<h1><a name="Introduction">1. Introduction</a></h1>
  
<p class="quote">
"Tell me what wines I should buy to serve with each course of the
following menu.  And, by the way, I don't like Sauternes."</p>

<p>
It would be difficult today to construct a Web agent that would be
capable of performing a search for wines on the Web that satisfied
this query.  Similarly, consider actually assigning a software agent
the task of making a coherent set of travel arrangements.  (For more
use cases see the <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Requirements">OWL requirements document</a>.)
</p>

<p>
To support this sort of computation, 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
<em>semantics</em> of the data.
</p>

<p>
<a id="term_ontology" name="term_ontology"></a>
The OWL Web Ontologoy Language is a language for defining and instantiating <em>Web
ontologies</em>.  <em>Ontology</em> 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.  An 
<a id="Owl_Ontology_definition" name="Owl_Ontology_definition">
<em>OWL ontology</em></a> may include
descriptions of <i>classes</i>, <i>properties</i> and their instances.
Given such an ontology, the 
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/"> 
OWL formal semantics</a> specifies how to derive its logical
consequences, i.e. facts not literally present in the ontology, but
<a id="term_entailed" name="term_entailed"></a><em>entailed</em> by the 
semantics.  These entailments may be based on
a single document or multiple distributed documents that have been
combined using defined <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#import">OWL mechanisms</a>.
</p>

<p>
This document is one component of the description of OWL, the Web Ontology
Language, being produced by the W3C Web Ontology Working Group (WebOnt).
The <a href="http://www.w3.org/TR/2004/REC-owl-features-20040210/#s1.1">
Document Roadmap</a>
section of the Overview (<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#FeatureList">[Overview]</a>, 1.1) 
describes each of the different parts and how they fit together.
</p>

<p> 
One question that comes up when describing yet another XML/Web 
standard is "What does this buy me that XML and XML Schema don't?"  
<!-- An operational consensus can always be developed over the meaning of a
set of XML tags and their contents.  There is furious ongoing
standards activity doing exactly this. 
</p>
<p> -->
There are two answers to this question.  
</p>
<ul>
<li>
An ontology differs from an XML schema in that it is a knowledge
representation, not a message format.  Most industry based Web
standards consist of a combination of message formats and protocol
specifications.  These formats have been given an operational
semantics, such as,  "Upon receipt of this <tt>PurchaseOrder</tt> message,
transfer <tt>Amount</tt> dollars from <tt>AccountFrom</tt> to
<tt>AccountTo</tt> and ship <tt>Product</tt>."  But the specification
is not designed to support reasoning outside the transaction context.
For example, we won't in general have a mechanism to conclude that
because the <tt>Product</tt> is a type of Chardonnay it must also be a
white wine.  <br /><br />
</li>

<li>
One advantage of OWL ontologies will be the availability of tools that
can reason about them.  Tools will provide <em>generic</em> support
that is not specific to the particular subject domain, which would be
the case if one were to build a system to reason about a specific
industry-standard XML schema.  Building a sound and useful reasoning
system is not a simple effort.  Constructing an ontology is much more
tractable.  It is our expectation that many groups will embark on
ontology construction.  They will benefit from third party tools based
on the formal properties of the OWL language, tools that will deliver
an assortment of capabilities that most organizations would be hard
pressed to duplicate.  <br />
</li>
</ul>


<h2><a name="OwlVarieties">1.1. The Species of OWL</a></h2>

<p>
The OWL language provides three increasingly expressive sublanguages
designed for use by specific communities of implementers and users.
</p>
<ul>
<li>
<p><a id="term_OWLLite" name="term_OWLLite"></a><em>OWL Lite</em> supports those users primarily needing a classification
  hierarchy and simple constraint features.   For example, while OWL Lite
  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 provide a quick migration path
  for thesauri and other taxonomies.   </p>
</li>

<li>
<p><a id="term_OWLDL" name="term_OWLDL"></a><em>OWL DL</em> supports those users
who want the maximum expressiveness without losing computational
completeness (all entailments are guaranteed to be computed) and decidability (all 
computations will finish in finite time) of reasoning systems.  
OWL DL includes all OWL language constructs
with restrictions such as type separation (a class can not also be an individual or
property, a property can not also be an individual or class).  
OWL DL is so named due to its correspondence with
  <em>description logics</em> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DescriptionLogics">[Description Logics]</a>, 
  a field of research that has studied a particular decidable fragment of 
  first order logic.  OWL DL was designed to support the existing Description Logic 
  business segment and has desirable computational properties 
  for reasoning systems.
</p>
</li>

<li>
<p><a id="term_OWLFull" name="term_OWLFull"></a><em>OWL Full</em> 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.  Another significant difference from
  OWL DL is that a <tt>owl:DatatypeProperty</tt> can be marked as
  an <tt>owl:InverseFunctionalProperty</tt>.  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 every feature of
OWL Full.  
<!-- DELETED
Some communities may find it useful 
to create other subsets of OWL Full than OWL DL that
have desireable computational properties while requiring 
a different set of constraints. -->
</p>
</li>
</ul>

<p>
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.
</p>
<ul>
<li>Every legal OWL Lite ontology is a legal OWL DL ontology. </li>
<li>Every legal OWL DL ontology is a legal OWL Full ontology. </li>
<li>Every valid OWL Lite conclusion is a valid OWL DL conclusion.</li>
<li>Every valid OWL DL conclusion is a valid OWL Full conclusion.</li>
</ul>

<p>
  Ontology developers adopting OWL should consider which species best
  suits their needs.  The choice between OWL Lite and OWL DL 
  depends on the extent to which users require the more expressive
  restriction constructs provided by OWL DL.  Reasoners for OWL
  Lite will have desirable computational properties.  Reasoners for
  OWL DL, while dealing with a decidable sublanguage, will be subject to
  higher worst-case complexity.
  The choice between OWL DL and OWL Full mainly
  depends on the extent to which users require the
  meta-modelling facilities of RDF Schema (i.e. defining classes of
  classes). 
  When using OWL Full as compared to OWL
  DL, reasoning support is less predictable. 
  For more information about this issue see the
  <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#FormalModel">OWL semantics document</a>.
</p>
<p>

Users migrating from RDF to OWL DL or OWL Lite need to take care to
ensure that the original RDF document complies with the constraints
imposed by OWL DL and OWL Lite. The details of these constraints are
explained in
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#app-DLinRDF">
Appendix E</a> of the OWL Reference.

</p>
<p>
<a name="OWL_DL_tag"></a>
<a name="OWL_Full_tag"></a>
When we introduce constructs that are only permitted in OWL DL or
OWL Full, they are marked by "[OWL DL]".  
</p>

<h2><a name="StructureOfDoc">1.2. Structure of the Document</a></h2>

<p> 
In order to provide a consistent set of examples throughout the
guide, we have created a <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine.rdf">wine</a> and 
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food.rdf">food</a> ontology.  This
is an OWL DL ontology.  Some of our discussion will
focus on OWL Full capabilities and is so marked.  

The wine and food ontology is a significant modification of an <a
href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#wine1">element</a> of the DAML ontology library with a long
history.  It was originally developed by McGuinness as a CLASSIC
description logic <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#wine3">example</a>, expanded to a 
description logic <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#wine4">tutorial</a>, and expanded to an ontology
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#wine2">tutorial</a>.
</p>

<p>
In this document we present examples using the 
<a href="http://www.w3.org/TR/REC-rdf-syntax/#grammar">RDF/XML syntax</a>
(<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#RDF1">[RDF]</a>, 5), 
assuming XML will be familiar
to the largest audience.  The normative OWL exchange syntax is RDF/XML.
Note that OWL has been designed for maximal compatibility
with RDF and RDF Schema.  These XML and RDF formats are part of the
OWL standard. 
</p>

<!--
Notes indicating expected changes pending clarification are marked
with '@@', e.g. [@@ Note].
-->

<p> 
All of the examples presented in this document are taken from the
ontologies contained in <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine.rdf">wine.rdf</a> and <a
href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food.rdf">food.rdf</a>, except those marked with <span
class="red">&nbsp;&not;&nbsp;</span> in the bottom right corner.
</p>

<hr />

<h1><a name="StructureOfOntologies">2. The Structure of Ontologies</a>
</h1>

<p>
OWL is a component of the <a
href="http://www.w3.org/2001/sw/"><i>Semantic Web</i></a>
activity. This effort aims to make Web resources more readily
accessible to automated processes by adding information about the resources
that describe or provide Web content.  
As the Semantic Web is inherently distributed, OWL must allow for information to be
gathered from distributed sources.  This is partly done by allowing
ontologies to be related, including explicitly importing
information from other ontologies.
</p>
<p>
In addition, OWL makes an <a id="term_openworld"
name="term_openworld"></a><em>open world</em> assumption.  That is,
descriptions of resources are not confined to a single file or scope.
While class <tt>C1</tt> may be defined originally in ontology O1, it
can be extended in other ontologies.  The consequences of these
additional propositions about <tt>C1</tt> are <a id="term_monotonic"
name="term_monotonic"></a><em>monotonic</em>.  New information cannot
retract previous information.  New information can be contradictory,
but facts and entailments can only be <em>added</em>, never
<em>deleted</em>.
</p>
<p>
The possibility of such contradictions is something the designer of an
ontology needs to take into consideration.  It is expected that tool
support will help detect such cases.
</p>

<p>
In order to write an ontology that can be interpreted
unambiguously and used by software agents we require a syntax and formal semantics for
OWL.   OWL is a vocabulary extension 
<a href="http://www.w3.org/TR/rdf-mt/">[RDF Semantics]</a> of RDF.
The OWL semantics are defined in
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#FormalModel"><i>OWL Web Ontology Language Semantics and Abstract Syntax</i></a>.
</p>


<h2><a name="Namespaces">2.1. Namespaces</a></h2>

<p>
Before we can use a set of terms, we need a precise indication of what
specific vocabularies are being used.  
A standard initial component of an ontology includes a set of
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#XMLNS"><em>XML namespace</em></a> declarations
enclosed in an opening <tt>rdf:RDF</tt> tag. 

These provide a means to unambiguously interpret identifiers and make
the rest of the ontology presentation much more readable.  A typical
OWL ontology begins with a <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#XMLNS">namespace declaration</a>
similar to the following.   Of course, the URIs of the defined
ontologies will not usually be w3.org references.
</p>


<pre>
&lt;rdf:RDF 
    xmlns     ="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#" 
    xmlns:vin ="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#"       
    xml:base  ="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#"       
    xmlns:food="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food#"    
    xmlns:owl ="http://www.w3.org/2002/07/owl#"
    xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"&gt; 
</pre>

<p>
The first two declarations identify the namespace associated with this
ontology.  The first makes it the <em>default</em> namespace, stating that
unprefixed qualified names refer to the current
ontology.  The second identifies the namespace of the current ontology
with the prefix <tt>vin:</tt>. The third identifies the base URI for
this document (see 
<a href="#owl_imports">
below </a>). The fourth identifies the namespace of
the supporting food ontology with the prefix <tt>food:</tt>. 
</p>

<p>
The fifth namespace declaration says that in this document, elements
prefixed with <tt>owl:</tt> should be understood as referring to
things drawn from the namespace called
<code>http://www.w3.org/2002/07/owl#</code>.  This is a conventional
OWL declaration, used to introduce the OWL vocabulary.
</p>

<p>
OWL depends on constructs defined by RDF, RDFS, and XML Schema datatypes.  
In this document, the <tt>rdf:</tt> prefix refers to things drawn from
the namespace called
<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>. The next two
namespace declarations make similar statements about the RDF Schema
(<tt>rdfs:</tt>) and XML Schema datatype (<tt>xsd:</tt>) namespaces.
</p>

<p>
As an aid to writing lengthy URLs it can often be
useful to provide a set of entity definitions in a document type
declaration (DOCTYPE) that precedes the ontology definitions.  The names defined by the namespace
declarations only have significance as parts of XML tags.  Attribute
values are <em>not</em> namespace sensitive.  But in OWL we frequently
reference ontology identifiers using attribute values.  They can be
written down in their fully expanded form, for
example "http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#merlot".  Alternatively,
abbreviations can be defined using an ENTITY definition, for example:
</p>
<pre>
&lt;!DOCTYPE rdf:RDF [
    &lt;!ENTITY vin  "http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#" &gt;
    &lt;!ENTITY food "http://www.w3.org/TR/2004/REC-owl-guide-20040210/food#" &gt; ]&gt;
</pre>
<p>
After this pair of ENTITY declarations, we could write the value
"&amp;vin;merlot" and it would expand to
"http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#merlot".
</p>
<p>
Perhaps more importantly, the <tt>rdf:RDF</tt> namespace declarations
can then be simplified so that changes made to the
entity declarations will propagate through the ontology consistently.
</p>
<pre>
&lt;rdf:RDF 
    xmlns     ="&amp;vin;" 
    xmlns:vin ="&amp;vin;" 
    xml:base  ="&amp;vin;" 
    xmlns:food="&amp;food;"
    xmlns:owl ="http://www.w3.org/2002/07/owl#"
    xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"&gt; 
</pre>

<h2><a id="OntologyHeaders" name="OntologyHeaders">2.2. Ontology Headers</a></h2>

<p><a id="owl_Ontology" name="owl_Ontology"></a>
Once namespaces are established we normally include a 
collection of  assertions about the ontology grouped under 
an <tt>owl:Ontology</tt> tag.  These tags support
such critical housekeeping tasks as comments, version control and
inclusion of other ontologies. 
</p>

<pre>
&lt;owl:Ontology rdf:about=""&gt; 
  &lt;rdfs:comment&gt;An example OWL ontology&lt;/rdfs:comment&gt;
  &lt;owl:priorVersion rdf:resource="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine"/&gt; 
  &lt;owl:imports rdf:resource="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food"/&gt; 
  &lt;rdfs:label&gt;Wine Ontology&lt;/rdfs:label&gt; 
  ...
</pre>

<p> 
Note that we use '...' to indicate that there is additional text that
has been elided for purposes of the example.
</p>

<p>
The <tt>owl:Ontology</tt> element is a place to collect much of
the OWL meta-data for the document.  It does not guarantee that the
document describes an ontology in the traditional sense.  
In some communities, ontologies
are not about individuals but only the classes and properties that define a domain.
When using OWL to describe a collection of instance data
the <tt>owl:Ontology</tt> tag may be needed in order to record version
information and to import the definitions that the document depends on.
Thus, in OWL the term <em>ontology</em> has been broadened to include
instance data (<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Owl_Ontology_definition">see above</a>).
</p>

<p>
<a id="owl_imports" name="owl_imports"></a>
<a id="rdfs_comment" name="rdfs_comment"></a>
The <tt>rdf:about</tt> attribute provides a name or reference for the ontology.
Where the value of the attribute is "", the standard case, the 
name of the ontology is the base URI of the <tt>owl:Ontology</tt> element.  
Typically, this is the URI of the document containing the ontology.
An exception to this is a context that makes use of <tt>xml:base</tt> 
which may set the base URI for an element to something other than the 
URI of the current document.
</p>

<p>
<tt>rdfs:comment</tt> provides the obvious needed capability
to annotate an ontology.
</p>

<p>
<tt>owl:priorVersion</tt> is a standard tag intended to provide
hooks for version control systems working with ontologies.  Ontology
versioning is discussed further <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyVersioning">below.</a>
</p>

<p>
<a id="term_import" name="term_import"></a>
<a id="import" name="import"><tt>owl:imports</tt></a>
provides an include-style mechanism.  
<tt>owl:imports</tt>
takes a single argument, identified by the <tt>rdf:resource</tt> attribute.
</p>

<p>
Importing another ontology brings the entire set of assertions 
provided by that ontology into the current ontology.
In order to make best use of this imported ontology it would normally
be coordinated with a namespace declaration.  Notice the distinction
between these two mechanisms.  The namespace declarations provide
a convenient means to <em>reference</em> names defined in other OWL
ontologies.

Conceptually, <tt>owl:imports</tt> is provided to indicate your
intention to <em>include</em> the assertions of the target ontology.
Importing another ontology, <em>O2</em>, will also import all of the
ontologies that <em>O2</em> imports.
</p>

<p>
Note that <tt>owl:imports</tt> may not always succeed.  As you would
expect when dealing with the Semantic Web, access to resources
distributed across the Web may not always be possible.  Tools will
respond to this situation in an implementation defined manner.
</p>

<p>
Note that in order to use the OWL vocabulary you do not need to
import the <a href="http://www.w3.org/2002/07/owl">owl.rdf</a>
ontology.  In fact, such an import is not recommended.
</p>

<p>
One common set of additional tags that could reasonably be included
here are some of the standard <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DublinCore">Dublin
Core</a> metadata tags.  The subset includes those that take simple
types or strings as values.  Examples include Title, Creator,
Description, Publisher, and Date (see 
<a href="http://purl.org/dc/elements/1.1/">RDF declarations</a>).
</p>

<p>
Properties that are used as annotations should be declared using 
<a id="owl_AnnotationProperty" name="owl_AnnotationProperty"></a>
<tt>owl:AnnotationProperty</tt>.  E.g.
</p>
<pre>
&lt;owl:AnnotationProperty rdf:about="&amp;dc;creator" /&gt;
</pre>

<p>
OWL provides several other mechanisms to tie the current ontology and
imported ontologies together (see <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyMapping">ontology
mapping</a>).
</p>
<p>
We also include an <tt>rdfs:label</tt> to
support a natural language label for our ontology.
</p>

<p>The ontology header definition is closed with
the following tag.
</p>
<pre>
&lt;/owl:Ontology&gt;
</pre>
<p>
This prelude is followed by the actual definitions that 
make up the ontology and is ultimately closed by 
</p>
<pre>
&lt;/rdf:RDF&gt;
</pre>
    
<h2><a id="Privacy" name="Privacy">2.3. Data Aggregation and Privacy</a></h2>

<p>
OWL's ability to express ontological information about instances
appearing in multiple documents supports linking of data from diverse
sources in a principled way.  The underlying semantics provides
support for inferences over this data that may yield unexpected
results.  In particular, the ability to express equivalences using
<tt>owl:sameAs</tt> can be used to state that seemingly
different individuals are actually the same.
<tt>Owl:InverseFunctionalProperty</tt> can also be used to link
individuals together.
For example, if a property such as "SocialSecurityNumber" is an
<tt>owl:InverseFunctionalProperty</tt>, then two separate individuals
could be inferred to be identical based on having the same value of
that property.  When individuals are determined to be the same by such
means, information about them from different sources can be
merged. This <i>aggregation</i> can be used to determine facts that
are not <i>directly</i> represented in any one source.
</p>

<p> 
The ability of the Semantic Web to link information from multiple
sources is a desirable and powerful feature that can be used in many
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#IntegratingApplications">applications</a>.
However, the capability to merge data from multiple sources, combined
with the inferential power of OWL, does have potential for abuse.
Users of OWL should be alert to the potential privacy implications.

Detailed security solutions were considered out of scope for the
Working Group.  A number of organizations are addressing these
issues with a variety of security and preference solutions. 
See for example
<a href="http://www.oasis-open.org/committees/security/charter.php">
SAML</a> and 
<a href="http://www.w3.org/P3P/">P3P</a>.
</p>

<hr />

<h1><a name="BasicDefinitions">3. Basic Elements</a></h1>

<p>
Most of the elements of an OWL ontology concern classes, properties,
instances of classes, and relationships between these instances.
This section presents the language components essential to introducing
these elements.
</p>

<h2><a name="SimpleClasses">3.1. Simple Classes and Individuals</a></h2>

<p>
Many uses of an ontology will depend on the ability to reason
about individuals.  In order to do this in a useful fashion we need to
have a mechanism to describe the classes that individuals belong to
and the properties that they inherit by virtue of class membership.
We can always assert specific properties about individuals, but much
of the power of ontologies comes from class-based reasoning.
</p>
<p>
Sometimes we want to emphasize the distinction between a class as an
object and a class as a set containing elements.  
We call the set of individuals that are members of a class 
the <a id="term_extension" name="term_extension"></a><em>extension</em> of the class.
</p>


<h3><a name="DefiningSimpleClasses">3.1.1. Simple Named Classes</a><br />
<tt>Class, rdfs:subClassOf</tt></h3>

<p>
<a id="owl_Thing" name="owl_Thing"></a>
<a id="owl_Nothing" name="owl_Nothing"></a>
The most basic concepts in a domain should correspond
to classes that are the roots of various 
taxonomic trees.  Every individual in the OWL world is a member of
the class
<tt>owl:Thing</tt>.  Thus each user-defined class 
is implicitly a subclass of <tt>owl:Thing</tt>.  Domain specific root classes are
defined by simply declaring a named class.
OWL also defines the empty class, <tt>owl:Nothing</tt>.
</p>

<p><a id="owl_Class" name="owl_Class"></a>
For our sample wines domain, we create three root classes: <tt>Winery</tt>,
<tt>Region</tt>, and <tt>ConsumableThing</tt>.  
</p>

<pre>
&lt;owl:Class rdf:ID="Winery"/&gt; 
&lt;owl:Class rdf:ID="Region"/&gt; 
&lt;owl:Class rdf:ID="ConsumableThing"/&gt; 
</pre>

<p>
Note that we have only said that there exist classes that have been 
given these names, indicated by the '<tt>rdf:ID=</tt>' syntax.  Formally, we
know almost nothing about these classes other than their existence,
despite the use of familiar English terms as labels.  And while the
classes exist, they may have no members.  For all we know at the
moment, these classes might as well have been called <tt>Thing1</tt>,
<tt>Thing2</tt>, and <tt>Thing3</tt>.
</p>
<p>
It is important to remember that definitions may be incremental and distributed.  
In particular, we will have more to say about <tt>Winery</tt> later.
</p>

<p>
The syntax <tt>rdf:ID="Region"</tt> is used to introduce a
name, as part of its definition. This is the
<a href="http://www.w3.org/TR/rdf-syntax-grammar/#idAttr">rdf:ID
attribute</a> (<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#RDF1">[RDF]</a>, 7.2.22) that is like the familiar ID attribute defined by XML.
Within this document, the <tt>Region</tt> class can now be referred to using 
<tt>#Region</tt>, e.g. <tt>rdf:resource="#Region"</tt>.  
Other ontologies may reference this
name using its complete form, 
<tt>"http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#Region"</tt>.
</p>

<p>
Another form of reference
uses the syntax <tt>rdf:about="#Region"</tt> to <a
href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DefiningIndividuals"><em>extend</em></a> the definition of a
resource.
This use of the <tt>rdf:about="&amp;ont;#x"</tt> syntax is a critical element
in the creation of a distributed ontology.  It permits the extension
of the imported definition of <tt>x</tt> without modifying the
original document and supports the incremental construction of a larger ontology.  
</p>
<p>
It is now possible to refer to the classes we defined in other OWL
constructs using their given identifier.  For the first class, within
this document, we can use the relative identifier, <tt>#Winery</tt>.
Other documents may need to reference this class as well.  The most
reasonable way to do so is to provide namespace and entity definitions
that include the defining document as a source:
</p>
<pre>
...
&lt;!ENTITY vin  "http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#" &gt;
&lt;!ENTITY food "http://www.w3.org/TR/2004/REC-owl-guide-20040210/food#" &gt;
...
&lt;rdf:RDF xmlns:vin ="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#"
         xmlns:food="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food#" ... &gt;
...
</pre>
<p>
Given these definitions we can refer to the winery class either
using the XML tag <tt>vin:Winery</tt> or the attribute value <tt>&amp;vin;Winery</tt>.
More literally, it is always possible to reference a resource using its full URI,
here <code>http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#Winery</code>.
</p>

<p>
The fundamental taxonomic constructor for
classes is <tt>rdfs:subClassOf</tt>.
It relates a more specific class to a more general
class.  If X is a subclass of Y, then every instance of X is also
an instance of Y.  
The <tt>rdfs:subClassOf</tt> relation is transitive.  If X is a subclass of Y
and Y a subclass of Z then X is a subclass of Z.  
</p>

<pre>
&lt;owl:Class rdf:ID="PotableLiquid"&gt; 
  &lt;rdfs:subClassOf rdf:resource="#ConsumableThing" /&gt;
  ...
&lt;/owl:Class&gt; 
</pre>

<p>
We define <tt>PotableLiquid</tt> (liquids suitable for drinking) to
be a subclass of <tt>ConsumableThing</tt>.  
</p>
<p>
In the world of Web-based ontologies, both of these classes
can be defined in a separate ontology that would provide the basic
building blocks for a wide variety of food and drink ontologies, which
is what we have done - they are defined in the
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/food.rdf">food</a> ontology, which 
is <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#import">imported</a> into the wine ontology.  
The food ontology includes a number of classes, for example
<tt>Food</tt>, <tt>EdibleThing</tt>, <tt>MealCourse</tt>, and
<tt>Shellfish</tt>, that do not belong in a collection of wine facts,
but must be connected to the wine vocabulary if we are going to
perform useful reasoning.  Food and wine are mutually
dependent, in order to satisfy our need to identify wine/food matches.
</p>

<p>
A class definition has two parts: a name introduction or reference 
and a list of restrictions.  Each of the immediate contained
expressions in the class definition further restricts the instances of
the defined class.  Instances of the class belong to the intersection of
the restrictions.  (Though see the details of <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_equivalentClass">
<tt>owl:equivalentClass</tt></a>.)
So far we have only seen examples that include a single restriction,
forcing the new class to be a subclass of some other named class.
</p>

<p>
<a id="rdfs_subClassOf" name="rdfs_subClassOf"></a>
<a id="rdfs_label" name="rdfs_label"></a>
At this point it is possible to create a simple (and incomplete)
definition for the class <tt>Wine</tt>.  <tt>Wine</tt> is a
<tt>PotableLiquid</tt>.  We also define <tt>Pasta</tt> as an 
<tt>EdibleThing</tt>.
</p>

<pre>
&lt;owl:Class rdf:ID="Wine"&gt; 
  &lt;rdfs:subClassOf rdf:resource="&amp;food;PotableLiquid"/&gt; 
  &lt;rdfs:label xml:lang="en"&gt;wine&lt;/rdfs:label&gt; 
  &lt;rdfs:label xml:lang="fr"&gt;vin&lt;/rdfs:label&gt; 
  ...  
&lt;/owl:Class&gt; 

&lt;owl:Class rdf:ID="Pasta"&gt;
  &lt;rdfs:subClassOf rdf:resource="#EdibleThing" /&gt;
  ...
&lt;/owl:Class&gt;
</pre>

<p>
The <tt>rdfs:label</tt> entry provides an optional human readable
name for this class.  Presentation tools can make use of it.
The "lang" attribute provides support for multiple languages.  A label
is like a comment and contributes nothing to the logical
interpretation of an ontology. </p>

<p>
Our wine definition is still very incomplete. We know nothing about
wines except that they are things and potable liquids, but we have
sufficient information to create and reason about individuals.
</p>

<h3><a name="DefiningIndividuals">3.1.2. Individuals</a></h3>

<p>
In addition to classes, we want to be able to describe their members.
We normally think of these as individuals in our universe of things.
An individual is minimally introduced by declaring it to be a member
of a class.
</p>
<pre>
&lt;Region rdf:ID="CentralCoastRegion" /&gt; 
</pre>

<p>
Note that the following is identical in meaning to the 
example above.  
<a id="rdf_type" name="rdf_type"></a>
</p>

<pre>
&lt;owl:Thing rdf:ID="CentralCoastRegion" /&gt; 

&lt;owl:Thing rdf:about="#CentralCoastRegion"&gt; 
   &lt;rdf:type rdf:resource="#Region"/&gt; 
&lt;/owl:Thing&gt;
</pre>

<p>
<tt>rdf:type</tt> is an RDF property that ties an individual to a class
   of which it is a member.
</p>

<p>
There are a couple of points to be made here. First,
we have decided that <tt>CentralCoastRegion</tt> (a specific area) is
member of <tt>Region</tt>, the class containing all geographical regions.   
Second, there is no requirement in the two-part example that the two
elements need to be adjacent to one another, or even in the same
file (though the names would need to be extended with a URI in such a
case).  We design Web ontologies to be distributed.  They can be
imported and augmented, creating derived ontologies.
</p>

<p>
In order to have available a few more classes for the
properties introduced in the next sections, we define a branch
of the <tt>Grape</tt> taxonomy, with an individual denoting the
Cabernet Sauvignon grape varietal.  Grapes are defined in the food ontology:
</p>
<pre>
&lt;owl:Class rdf:ID="Grape"&gt;
  ...
&lt;/owl:Class&gt;
</pre>
<p>
And then in the wine ontology we have:
</p>
<pre>
&lt;owl:Class rdf:ID="WineGrape"&gt;
  &lt;rdfs:subClassOf rdf:resource="&amp;food;Grape" /&gt;
&lt;/owl:Class&gt;

&lt;WineGrape rdf:ID="CabernetSauvignonGrape" /&gt;
</pre>

<p>
<!-- this means that we have in some sense limited our ontology
for specific purposes.  Because it is itself an individual,
we cannot create an instance of <tt>CabernetSauvignonGrape</tt>. 
If we needed to talk about individual grapes or specific bunches of grapes, we would have
designed the ontology differently. -->

As discussed in the next section,
<tt>CabernetSauvignonGrape</tt> is an individual because it denotes a
single grape varietal. 
</p>

<h3><a name="DesignForUse">3.1.3. Design for Use</a></h3>

<p>
<a id="term_class" name="term_class"></a>
<a id="term_individual" name="term_individual"></a>
There are important issues regarding the distinction between a <i>class</i> and
an <i>individual</i> in OWL.  A class is simply a name and collection of properties
that describe a set of individuals. Individuals are the members of those sets.
Thus classes should correspond to naturally occurring sets of things in a domain
of discourse, and individuals should correspond to actual entities that can be grouped
into these classes.
</p>
<p>
In building ontologies, this distinction is frequently blurred in two ways:
</p>

<ul>
  <li>
  <i>Levels of representation:</i> In certain contexts something 
  that is obviously a class can itself be considered an instance of something else.  For
  example, in the wine ontology we have the notion of a <tt>Grape</tt>, which is 
  intended to denote the set of all <i>grape varietals.</i>   
  <tt>CabernetSauvingonGrape</tt> is
  an example instance of this class, as it denotes the actual grape varietal 
  called Cabernet Sauvignon.
  However, <tt>CabernetSauvignonGrape</tt> could itself be considered a class, the set of all
  actual Cabernet Sauvignon grapes.  
  <br />
  <br />
</li>

<li>
<a id="instance-of" name="instance-of"></a>
<a id="term_instanceOf" name="term_instanceOf"></a>
<i>Subclass vs. instance:</i> It is very easy to confuse the 
instance-of relationship with the subclass relationship.  
For example, it may seem arbitrary to choose to make <tt>CabernetSauvignonGrape</tt>
an individual that is an instance of <tt>Grape,</tt> as opposed to a subclass of <tt>Grape</tt>.
This is not an arbitrary
decision.  The <tt>Grape</tt>  class denotes the set of all
<i>grape varietals</i>, and therefore any subclass of <tt>Grape</tt>  should denote a subset of these
varietals. Thus, CabernetSauvignonGrape should be considered an
<a id="term_instance" name="term_instance"></a><em>instance of</em> Grape, and not a subclass. It does not
describe a subset of Grape varietals, it <em>is</em> a grape varietal.
</li>
</ul>

<p>
Note that the same distinction arises with the treatment of the
<tt>Wine</tt> class.  The <tt>Wine</tt> class actually denotes the set
of all <em>varieties</em> of wine, not the set of actual bottles that
someone may purchase.

In an alternate ontology, each instance of <tt>Wine</tt> in the current
ontology could instead designate a class
consisting of all the bottles of wine of that type.  It is easy to
imagine an information system, such as an inventory system for a wine
merchant, that needs to consider individual bottles of wine.  

The wine ontology as it currently exists would require the ability to
treat classes as instances in order to support such an interpretation.

Note that OWL Full permits such expressivity, 
allowing us to treat an instance of a wine variety simultaneously 
as a class whose instances are bottles of wine.

</p>

<p>
In a similar vein, the wines produced by wineries in specific years
are considered vintages.  In order to represent the notion of a
vintage, we must determine where it fits in the current ontology.  An
instance of the <tt>Wine</tt> class, as discussed above, represents a
single variety of wine produced by a single winery, for example
<tt>FormanChardonnay.</tt>
</p>

<p>
Adding that the wine produced in the year 2000 is considered a 
<a id="vintageIntro" name="vintageIntro">vintage</a>
poses a challenge, because we don't have the ability to represent a
subset of a given wine individual.  This vintage is not a new
variety of wine, it is a special subset of the wine - that produced in
the year 2000.  

An option would be to use OWL Full and treat the wine instances as
classes with subclasses (subsets) denoting vintages. Another option is
to use a workaround and to consider <tt>Vintage</tt> as a separate class whose
instances have a relationship to the Wine they are a vintage of.

For example, <tt>FormanChardonnay2000</tt> is an
individual <tt>Vintage</tt> with a <tt>vintageOf</tt> property whose value is
the <tt>Wine</tt>, <tt>FormanChardonnay.</tt> We define the 
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#vintage"><tt>Vintage</tt></a> class below.
</p>

<p>
The point of this
discussion is to note that the development of an ontology should be
firmly driven by the intended usage.  These issues also underlie
one major difference between OWL Full and OWL DL. OWL Full
allows the use of classes as instances and OWL DL does not.
The wine ontology is designed to work in OWL DL, and
as a result individuals like <tt>FormanChardonnay</tt> are not 
simultaneously treated as classes.
</p>


<h2><a name="SimpleProperties">3.2. Simple Properties </a></h2>

<p>This world of classes and individuals would be pretty uninteresting
if we could only define taxonomies.  
<a id="term_Properties" name="term_Properties"></a><em>Properties</em> let us assert
general facts about the members of classes and specific facts about
individuals. 
</p>

<h3><a name="DefiningProperties">3.2.1. Defining Properties</a><br /> 
<tt>ObjectProperty, DatatypeProperty, rdfs:subPropertyOf, <br />
rdfs:domain, rdfs:range</tt></h3>

<p>A property is a binary relation. 
Two types of properties are distinguished:
</p>

<ul>
<li>
<a id="term_datatypeproperties" name="term_datatypeproperties"></a><em>datatype properties</em>, 
relations between instances of
classes and RDF literals and XML Schema datatypes</li>

<li><a id="term_objectproperties" name="term_objectproperties"></a><em>object properties</em>, 
relations between instances of two classes.
Note that the name <i>object</i> property is not intended to reflect a
connection with the <a href="http://www.w3.org/RDF/">RDF</a> term <a
href="http://www.w3.org/TR/rdf-schema/#ch_object">rdf:object</a>
(<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#RDF1">[RDF]</a>, 5.3.4).
</li>
</ul>

<p>
<a id="owl_ObjectProperty" name="owl_ObjectProperty"></a>
<a id="term_domain" name="term_domain"></a>
<a id="term_range" name="term_range"></a>
<a id="rdfs_domain" name="rdfs_domain"></a>
<a id="rdfs_range" name="rdfs_range"></a>
When we define a property
there are a number of ways to restrict the relation.
The domain and range can be specified.  The property can be defined to
be a specialization (subproperty) of an existing property.  More elaborate
restrictions are possible and are described  
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#PropertyCharacteristics">later</a>. 
</p>

<pre>
&lt;owl:ObjectProperty rdf:ID="madeFromGrape"&gt; 
  &lt;rdfs:domain rdf:resource="#Wine"/&gt;
  &lt;rdfs:range rdf:resource="#WineGrape"/&gt; 
&lt;/owl:ObjectProperty&gt; 

&lt;owl:ObjectProperty rdf:ID="course"&gt;
  &lt;rdfs:domain rdf:resource="#Meal" /&gt;
  &lt;rdfs:range rdf:resource="#MealCourse" /&gt;
&lt;/owl:ObjectProperty&gt;
</pre>

<p>
<a id="rdfs_subPropertyOf" name="rdfs_subPropertyOf"></a>
In OWL, a sequence of elements without an explicit operator
represents an implicit conjunction.   
The property <tt>madeFromGrape</tt> has a domain of <tt>Wine</tt>
<em>and</em> a range of <tt>WineGrape</tt>.  That is, it relates
instances of the class <tt>Wine</tt> to instances of the class
<tt>WineGrape</tt>.   Multiple domains mean that the 
domain of the property is the intersection of
the identified classes (and similarly for range). 
</p>
<p>
Similarly, the property <tt>course</tt> ties a <tt>Meal</tt> to a <tt>MealCourse</tt>.
</p>
<p>
Note that the use of range and domain information in OWL is different
from type information in a programming language.  Among other things, types
are used to check consistency in a programming language.  In OWL, a range may be
used to infer a type.  For example, given:
</p>
<pre>
&lt;owl:Thing rdf:ID="LindemansBin65Chardonnay"&gt;
  &lt;madeFromGrape rdf:resource="#ChardonnayGrape" /&gt;
&lt;/owl:Thing&gt;                                             <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>
we can infer that <tt>LindemansBin65Chardonnay</tt> is a wine because
the domain of <tt>madeFromGrape</tt> is <tt>Wine</tt>.
</p>
<p>
Properties, like classes, can be arranged in a hierarchy.
</p>
<pre>
&lt;owl:Class rdf:ID="WineDescriptor" /&gt;

&lt;owl:Class rdf:ID="WineColor"&gt;
  &lt;rdfs:subClassOf rdf:resource="#WineDescriptor" /&gt;
  ...
&lt;/owl:Class&gt;

&lt;owl:ObjectProperty rdf:ID="hasWineDescriptor"&gt;
  &lt;rdfs:domain rdf:resource="#Wine" /&gt;
  &lt;rdfs:range  rdf:resource="#WineDescriptor" /&gt;
&lt;/owl:ObjectProperty&gt;

&lt;owl:ObjectProperty rdf:ID="hasColor"&gt;
  &lt;rdfs:subPropertyOf rdf:resource="#hasWineDescriptor" /&gt;
  &lt;rdfs:range rdf:resource="#WineColor" /&gt;
  ...
&lt;/owl:ObjectProperty&gt;
</pre>
<p>
<tt>WineDescriptor</tt> properties relate wines to their color and components of their
taste, including sweetness, body, and flavor.  <tt>hasColor</tt>  is a
subproperty of the <tt>hasWineDescriptor</tt> property, with its range 
further restricted to <tt>WineColor</tt>.  The <tt>rdfs:subPropertyOf</tt>
relation in this case means that anything with a <tt>hasColor</tt>
property with value X also has a <tt>hasWineDescriptor</tt> property
with value X.
</p>

<p>
Next we introduce the <tt>locatedIn</tt> property, which relates things to
the regions they are located in.  
</p>
<pre>
&lt;owl:ObjectProperty rdf:ID="locatedIn"&gt;
  ...
  &lt;rdfs:domain rdf:resource="http://www.w3.org/2002/07/owl#Thing" /&gt;
  &lt;rdfs:range rdf:resource="#Region" /&gt;
&lt;/owl:ObjectProperty&gt;
</pre>
<p>
Notice how the domain and range of <tt>locatedIn</tt> are defined.
The domain permits anything to be located in a region, including
regions themselves.  And the 
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_TransitiveProperty">transitive</a> 
composition of this relation
essentially creates a network of geographically included subregions
and things.  Those things that have nothing located in them
can be of any class, while those that contain others must be
regions.
</p>

<p>
It is now possible to expand the definition of <tt>Wine</tt> to
include the notion that a wine is 
made from at least one <tt>WineGrape</tt>.
As with property definitions, class definitions have multiple subparts that are
implicitly conjoined.
</p>

<pre>
&lt;owl:Class rdf:ID="Wine"&gt; 
  &lt;rdfs:subClassOf rdf:resource="&amp;food;PotableLiquid"/&gt; 
  &lt;rdfs:subClassOf&gt;
<span class="highlight">    &lt;owl:Restriction&gt; 
      &lt;owl:onProperty rdf:resource="#madeFromGrape"/&gt;
      &lt;owl:minCardinality rdf:datatype="&amp;xsd;nonNegativeInteger"&gt;1&lt;/owl:minCardinality&gt;
    &lt;/owl:Restriction&gt; </span>
  &lt;/rdfs:subClassOf&gt;
  ...  
&lt;/owl:Class&gt;
</pre>
<p>
The highlighted subclass restriction above
</p>
<pre>
    &lt;owl:Restriction&gt; 
      &lt;owl:onProperty rdf:resource="#madeFromGrape"/&gt;
      &lt;owl:minCardinality rdf:datatype="&amp;xsd;nonNegativeInteger"&gt;1&lt;/owl:minCardinality&gt;
    &lt;/owl:Restriction&gt; 
</pre>
<p>
defines an unnamed class that represents the set of things
with at least one <tt>madeFromGrape</tt> property.   
We call these <a id="term_anonymousClass" name="term_anonymousClass"></a><em>anonymous</em>
classes.  Including this restriction in the <tt>Wine</tt>
class definition body states that things that are wines are also
members of this anonymous class.  That is, every individual wine must participate
in at least one <tt>madeFromGrape</tt> relation.  
</p>

<p>
<a id="vintage" name="vintage" />
We can now describe the class of <tt>Vintage</tt>s, discussed <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#vintageIntro">previously</a>.
</p>

<pre>
&lt;owl:Class rdf:ID="Vintage"&gt; 
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt; 
      &lt;owl:onProperty rdf:resource="#vintageOf"/&gt;
      &lt;owl:minCardinality rdf:datatype="&amp;xsd;nonNegativeInteger"&gt;1&lt;/owl:minCardinality&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
&lt;/owl:Class&gt;                                             <span class="red">&nbsp;&not;&nbsp;</span>
</pre>

<p>
The property <tt>vintageOf</tt> ties a <tt>Vintage</tt> to a
<tt>Wine</tt>.
</p>

<pre>
&lt;owl:ObjectProperty rdf:ID="vintageOf"&gt;
  &lt;rdfs:domain rdf:resource="#Vintage" /&gt;
  &lt;rdfs:range  rdf:resource="#Wine" /&gt;
&lt;/owl:ObjectProperty&gt;                                    <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>
We relate <tt>Vintage</tt>s to their years in the next section.
</p>

<h3><a name="rdfs_Datatype"></a>
<a id="term_datatype" name="term_datatype"></a>
<a name="Datatypes1">3.2.2. Properties and Datatypes</a></h3>

<p>
We distinguish
properties according to whether they relate individuals to individuals
(object properties) or individuals to datatypes (datatype properties). 
Datatype properties may range over RDF literals or
simple types defined in accordance with 
<a href="http://www.w3.org/TR/xmlschema-2/">XML Schema datatypes</a>.
</p>

<p>
<a id="owl_DatatypeProperty" name="owl_DatatypeProperty"></a>
OWL uses most of the built-in XML
Schema datatypes.  References to these datatypes are by 
means of the URI reference for the datatype,
<tt>http://www.w3.org/2001/XMLSchema</tt>. The following datatypes are
<em>recommended</em> for use with OWL: 
</p>

<table class="info">
  <tbody>
<tr><td>xsd:string</td><td>xsd:normalizedString</td><td>xsd:boolean</td></tr> 
<tr><td>xsd:decimal</td><td>xsd:float</td><td>xsd:double</td></tr>
<tr><td>xsd:integer</td><td>xsd:nonNegativeInteger</td><td>xsd:positiveInteger</td></tr> 
<tr><td>xsd:nonPositiveInteger</td><td>xsd:negativeInteger</td></tr> 

<tr><td>xsd:long</td><td>xsd:int</td><td>xsd:short</td><td>xsd:byte</td></tr> 
<tr><td>xsd:unsignedLong</td><td>xsd:unsignedInt</td><td>xsd:unsignedShort</td><td>xsd:unsignedByte</td></tr> 
<tr><td>xsd:hexBinary</td><td>xsd:base64Binary</td></tr> 
<tr><td>xsd:dateTime</td><td>xsd:time</td><td>xsd:date</td><td>xsd:gYearMonth</td></tr> 
<tr><td>xsd:gYear</td><td>xsd:gMonthDay</td><td>xsd:gDay</td><td>xsd:gMonth</td></tr>
<tr><td>xsd:anyURI</td><td>xsd:token</td><td>xsd:language</td></tr> 
<tr><td>xsd:NMTOKEN</td><td>xsd:Name</td><td>xsd:NCName</td></tr>
  </tbody>
</table>
<p>
The above datatypes, plus <tt>rdfs:Literal</tt>, form the built-in OWL datatypes. 
All OWL reasoners are required to support the <tt>xsd:integer</tt>
and <tt>xsd:string</tt> datatypes.
</p>

<p>
Other built-in XML Schema datatypes may
be used in OWL Full, but with caveats described in the 
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/syntax.html">
OWL Semantics and Abstract Syntax</a> documentation.  
</p>

<pre>
&lt;owl:Class rdf:ID="VintageYear" /&gt;

&lt;owl:DatatypeProperty rdf:ID="yearValue"&gt;
  &lt;rdfs:domain rdf:resource="#VintageYear" /&gt;    
  &lt;rdfs:range  rdf:resource="&amp;xsd;positiveInteger"/&gt;
&lt;/owl:DatatypeProperty&gt; 
</pre>

<p>
The <tt>yearValue</tt> property relates <tt>VintageYear</tt>s to positive
integer values.  
We introduce the <tt>hasVintageYear</tt> property, which relates a <tt>Vintage</tt> to a
<tt>VintageYear</tt> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#FunctionalProperty">below.</a>
</p> 

<p>
The <a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#EnumeratedDatatype">
OWL Reference</a> ([Reference], 6.2) describes the use of <tt>owl:oneOf</tt> and
<tt>rdf:List</tt> and <tt>rdf:rest</tt> to define an enumerated
datatype.  The example shows how to construct the <tt>owl:DatatypeProperty</tt>,
<tt>tennisGameScore</tt>, with a range equal to the elements of the list of integer 
values {0, 15, 30, 40}. 
</p>

<h3><a name="PropertiesOfIndividuals">3.2.3. Properties of Individuals</a></h3>

<p>
First we describe <tt>Region</tt> and <tt>Winery</tt> individuals, and then
we define our first wine, a Cabernet Sauvignon. 
</p>

<pre>
&lt;Region rdf:ID="SantaCruzMountainsRegion"&gt;
  &lt;locatedIn rdf:resource="#CaliforniaRegion" /&gt;
&lt;/Region&gt;

&lt;Winery rdf:ID="SantaCruzMountainVineyard" /&gt;

&lt;CabernetSauvignon
  rdf:ID="SantaCruzMountainVineyardCabernetSauvignon" &gt;<a id="CabernetSauvignon" name="CabernetSauvignon" />
  &lt;locatedIn   rdf:resource="#SantaCruzMountainsRegion"/&gt;  
  &lt;hasMaker    rdf:resource="#SantaCruzMountainVineyard" /&gt;   
&lt;/CabernetSauvignon&gt;  
</pre>

<p>
This is still incomplete.  There are other aspects of the wine flavor
that are defined in the full ontology.  But the pieces are falling
together.  We could begin reasoning about what menu items in our food
ontology this wine might
accompany.  We know from the definition above that the Santa Cruz
Mountain Vineyard makes it.
Because it is a Cabernet Sauvignon (see <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine.rdf">wine.rdf</a>),
we know it is a dry, red wine. 
</p>

<p>
Datatype properties can be added to individuals in a similar
fashion. Below we describe an instance of <tt>VintageYear</tt> and tie it to a
specific value of type <tt>&amp;xsd:positiveInteger</tt>.
</p>

<pre>
&lt;VintageYear rdf:ID="Year1998"&gt;
  &lt;yearValue rdf:datatype="&amp;xsd;positiveInteger"&gt;1998&lt;/yearValue&gt;
&lt;/VintageYear&gt; 
</pre>

<h2><a id="PropertyCharacteristics" name="PropertyCharacteristics">
3.3. Property Characteristics</a></h2>

<p>
The next few sections describe the mechanisms used to further specify
properties.  It is possible to specify property
<a id="term_characteristics" name="term_characteristics"></a><em>characteristics</em>, which provides a powerful mechanism for enhanced
reasoning about a property.
</p>

<h3>
<a id="TransitiveProperty" name="TransitiveProperty"></a> 
<a id="owl_TransitiveProperty" name="owl_TransitiveProperty"></a> 
3.3.1. TransitiveProperty
</h3>

<p>
If a property, P, is specified as transitive then for any x, y, and z:
</p> 

<pre>
P(x,y) and P(y,z) implies P(x,z)
</pre>

<p> 
The property <tt>locatedIn</tt> is transitive.
</p> 

<pre>
&lt;owl:ObjectProperty rdf:ID="locatedIn"&gt;
  &lt;rdf:type rdf:resource="&amp;owl;TransitiveProperty" /&gt;
  &lt;rdfs:domain rdf:resource="&amp;owl;Thing" /&gt;
  &lt;rdfs:range rdf:resource="#Region" /&gt;
&lt;/owl:ObjectProperty&gt;

&lt;Region rdf:ID="SantaCruzMountainsRegion"&gt;
  &lt;locatedIn rdf:resource="#CaliforniaRegion" /&gt;
&lt;/Region&gt;

&lt;Region rdf:ID="CaliforniaRegion"&gt;
  &lt;locatedIn rdf:resource="#USRegion" /&gt;
&lt;/Region&gt;
</pre>

<p> 
Because the <tt>SantaCruzMountainsRegion</tt> is <tt>locatedIn</tt> the
<tt>CaliforniaRegion</tt>, then it must also be <tt>locatedIn</tt> the 
<tt>USRegion</tt>, since <tt>locatedIn</tt> is transitive.
</p>

<h3>
<a id="SymmetricProperty" name="SymmetricProperty"></a> 
<a id="owl_SymmetricProperty" name="owl_SymmetricProperty"></a> 
3.3.2. SymmetricProperty
</h3>

<p>
If a property, P, is tagged as
symmetric then for any x and y: 
</p>
<pre>
P(x,y) iff P(y,x)
</pre> 
<p>
The property <tt>adjacentRegion</tt> is symmetric, while <tt>locatedIn</tt> is not.  
To be more precise, <tt>locatedIn</tt> is not intended to be
symmetric.  Nothing in the wine ontology at present prevents it from being symmetric.

</p>
<pre>
&lt;owl:ObjectProperty rdf:ID="adjacentRegion"&gt;
  &lt;rdf:type rdf:resource="&amp;owl;SymmetricProperty" /&gt;
  &lt;rdfs:domain rdf:resource="#Region" /&gt;
  &lt;rdfs:range rdf:resource="#Region" /&gt;
&lt;/owl:ObjectProperty&gt;

&lt;Region rdf:ID="MendocinoRegion"&gt;
  &lt;locatedIn rdf:resource="#CaliforniaRegion" /&gt;
  &lt;adjacentRegion rdf:resource="#SonomaRegion" /&gt;
&lt;/Region&gt;
</pre>  
<p>
The <tt>MendocinoRegion</tt> is adjacent to the <tt>SonomaRegion</tt>
and vice-versa.  The <tt>MendocinoRegion</tt> is located in the
<tt>CaliforniaRegion</tt> but not vice versa.
</p>

<h3>
<a id="FunctionalProperty" name="FunctionalProperty"></a> 
<a id="owl_FunctionalProperty" name="owl_FunctionalProperty"></a> 
3.3.3. FunctionalProperty
</h3>

<p>
If a property, P, is tagged as functional then for all x, y, and z:
</p>
<pre>
P(x,y) and P(x,z) implies y = z 
</pre>
<p>
In our wine ontology, <tt>hasVintageYear</tt>
is functional.  A wine has a unique vintage year.
That is, a given individual <tt>Vintage</tt> can only be associated with a
single year using the <tt>hasVintageYear</tt> property.
It is not a requirement of a <tt>owl:FunctionalProperty</tt>
that all elements of the domain have values. See the discussion of 
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#simpleCardinality"><tt>Vintage</tt> cardinality</a>. 
</p>
<pre>
&lt;owl:Class rdf:ID="VintageYear" /&gt;

&lt;owl:ObjectProperty rdf:ID="hasVintageYear"&gt;
  &lt;rdf:type rdf:resource="&amp;owl;FunctionalProperty" /&gt;
  &lt;rdfs:domain rdf:resource="#Vintage" /&gt;
  &lt;rdfs:range  rdf:resource="#VintageYear" /&gt;
&lt;/owl:ObjectProperty&gt;
</pre>

<h3>
<a id="inverseOf" name="inverseOf"></a> 
<a id="owl_inverseOf" name="owl_inverseOf"></a> 
3.3.4. inverseOf
</h3>

<p>If a property, P1, is tagged as the <tt>owl:inverseOf</tt> P2, then for
all x and y:
</p>

<pre>
P1(x,y) iff P2(y,x)
</pre>

<p>
Note that the syntax for <tt>owl:inverseOf</tt> takes a property name as an argument.
<tt>A iff B</tt> means <tt>(A implies B) and (B implies A)</tt>.
</p>

<pre>
&lt;owl:ObjectProperty rdf:ID="hasMaker"&gt;
  &lt;rdf:type rdf:resource="&amp;owl;FunctionalProperty" /&gt;
&lt;/owl:ObjectProperty&gt;
  
&lt;owl:ObjectProperty rdf:ID="producesWine"&gt;
  &lt;owl:inverseOf rdf:resource="#hasMaker" /&gt;
&lt;/owl:ObjectProperty&gt;
</pre>

<p>
<tt>Wine</tt>s have makers, which in the definition of <tt>Wine</tt>
are restricted to <tt>Winery</tt>s.  Then each 
<tt>Winery</tt> produces the set of wines that identify it as maker.
</p>

<h3>
<a id="InverseFunctionalProperty" name="InverseFunctionalProperty"></a> 
<a id="owl_InverseFunctionalProperty" name="owl_InverseFunctionalProperty"></a> 
3.3.5. InverseFunctionalProperty
</h3>

<p> 
If a property, P, is tagged as InverseFunctional then for all x, y and z:
</p>

<pre>
P(y,x) and P(z,x) implies y = z 
</pre>

<p>
Notice that <tt>producesWine</tt> in the preceding section is inverse
functional.  The reason is that the inverse of a functional property
must be inverse functional.  We could have defined <tt>hasMaker</tt>
and <tt>producesWine</tt> as follows and achieved the identical
effect as the preceding example.
</p>

<pre>
&lt;owl:ObjectProperty rdf:ID="hasMaker" /&gt;
  
&lt;owl:ObjectProperty rdf:ID="producesWine"&gt;
  &lt;rdf:type rdf:resource="&amp;owl;InverseFunctionalProperty" /&gt;
  &lt;owl:inverseOf rdf:resource="#hasMaker" /&gt;
&lt;/owl:ObjectProperty&gt;                                    <span class="red">&nbsp;&not;&nbsp;</span>
</pre>

<p>
Think of the elements of the range in an inverse functional property
as defining a unique key in the database sense.  
<tt>owl:InverseFunctional</tt> implies that the elements of the range
provide a unique identifier for each element of the domain.
</p>
<p>
<a id="rdfs_Literal" name="rdfs_Literal" />
In OWL Full, we can tag a <tt>DatatypeProperty</tt> as
inverseFunctional.  This permits us to identify a string as 
a unique key.  In OWL DL literals are disjoint from owl:Thing, which
is why OWL DL does not permit <tt>InverseFunctional</tt> to be applied to
<tt>DatatypeProperty</tt>.
</p>

<h2>
<a id="PropertyRestrictions" name="PropertyRestrictions"></a>
<a id="restrictions" name="restrictions"></a>
3.4. Property Restrictions</h2>

<p>
<a id="owl_Restriction" name="owl_Restriction"></a>
<a id="owl_onProperty" name="owl_onProperty"></a>
In addition to designating property characteristics, it is possible to
further constrain the range of a property in specific contexts in a
variety of ways.
We do this with <i>property restrictions</i>.  The various 
forms described below can only be used within the context of an <tt>owl:Restriction</tt>. 
The <tt>owl:onProperty</tt> element indicates the restricted property.   
</p>
<h3>
<a id="allValuesFrom" name="allValuesFrom"></a> 
<a id="someValuesFrom" name="someValuesFrom"></a>
<a id="owl_allValuesFrom" name="owl_allValuesFrom"></a> 
<a id="term_restriction_class" name="term_restriction_class"></a>
3.4.1. allValuesFrom, someValuesFrom</h3>

<p>
We have already seen one way to restrict the types of the elements that
make up a property.  The mechanisms to
date have been <em>global</em> in that they apply to all
instances of the property.  These next two, <tt>allValuesFrom</tt> and
<tt>someValuesFrom</tt>, are <em>local</em> to their containing class definition.
</p>
<p>
<!-- The <tt>owl:allValuesFrom</tt> restriction means that every instance of
the class must have an instance of the specified property with 
values that are all instances of the specified restriction class. -->

The <tt>owl:allValuesFrom</tt> restriction requires that for every instance of
the class that has instances of the specified property, the 
values of the property are all members of the class indicated by the
<tt>owl:allValuesFrom</tt> clause.
</p>
<pre>
&lt;owl:Class rdf:ID="Wine"&gt;
  &lt;rdfs:subClassOf rdf:resource="&amp;food;PotableLiquid" /&gt;
  ...
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#hasMaker" /&gt;
      &lt;owl:allValuesFrom rdf:resource="#Winery" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
  ...
&lt;/owl:Class&gt;
</pre>

<p>
The maker of a <tt>Wine</tt> must be a <tt>Winery</tt>.
The <tt>allValuesFrom</tt> restriction is on the <tt>hasMaker</tt> property of
this <tt>Wine</tt> class <em>only</em>.  Makers of <tt>Cheese</tt> are
not constrained by this local restriction.
</p>

<p>
<a id="owl_someValuesFrom" name="owl_someValuesFrom"></a>
<tt>owl:someValuesFrom</tt> is similar.   If we
replaced <tt>owl:allValuesFrom</tt> with <tt>owl:someValuesFrom</tt>
in the example above, it would mean that at least <em>one</em> of the
<tt>hasMaker</tt> properties of a <tt>Wine</tt> must point to an
individual that is a <tt>Winery</tt>.  
</p>

<pre>
&lt;owl:Class rdf:ID="Wine"&gt;
  &lt;rdfs:subClassOf rdf:resource="&amp;food;PotableLiquid" /&gt;
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#hasMaker" /&gt;
      &lt;owl:someValuesFrom rdf:resource="#Winery" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
  ...
&lt;/owl:Class&gt;                                            <span class="red">&nbsp;&not;&nbsp;</span>
</pre>

<p>
The difference between the two formulations is the difference between
a universal and existential quantification.
</p>

<table class="propositions">
  <tbody>
<tr><th>Relation</th><th>Implications</th></tr>
<tr><td>allValuesFrom</td><td>For all wines, if they have
makers, all the makers are wineries.</td></tr>
<tr><td>someValuesFrom&nbsp;&nbsp;</td><td>For all wines, they have at least one maker that is a winery.</td></tr>
  </tbody>
</table>

<p>
The first does not require a wine to have a maker.  If it does have one or more, they
must all be wineries.  The second requires that there be at least one maker
that is a winery, but there may be makers that are not wineries.
</p>

<h3><a id="simpleCardinality" name="simpleCardinality">3.4.2. Cardinality</a></h3>

<p>
<a id="owl_cardinality" name="owl_cardinality"></a>
<a id="term_cardinality" name="term_cardinality"></a>
We have already seen examples of cardinality constraints.  To date, 
they have been assertions about minimum cardinality.  Even more
straight-forward is <tt>owl:cardinality</tt>, which permits the
specification of <em>exactly</em> the number of elements in a relation.
For example, we specify <tt>Vintage</tt> to be a class  with 
exactly one <tt>VintageYear</tt>. 
</p>

<pre>
&lt;owl:Class rdf:ID="Vintage"&gt; 
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#hasVintageYear"/&gt;  
      &lt;owl:cardinality rdf:datatype="&amp;xsd;nonNegativeInteger"&gt;1&lt;/owl:cardinality&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
&lt;/owl:Class&gt;
</pre>

<p>
We specified <tt>hasVintageYear</tt> to be a functional property, which 
is the same as saying that every Vintage has at most one VintageYear. 
This application of that property to <tt>Vintage</tt> using the
cardinality restriction asserts
something stronger, that <em>every</em> <tt>Vintage</tt> has
<em>exactly</em> one <tt>VintageYear</tt>.
</p>
<!--
<p>
As another example, the following asserts that a <tt>Meal</tt> has at least
two <tt>course</tt>s.
</p>
<pre>
&lt;owl:Class rdf:ID="Meal"&gt;
  &lt;rdfs:subClassOf rdf:resource="#ConsumableThing" /&gt;
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#course" /&gt;
      &lt;owl:minCardinality rdf:datatype="&amp;xsd;nonNegativeInteger"&gt;1&lt;/owl:minCardinality&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
  ...
&lt;/owl:Class&gt;
</pre>
-->
<p>
<a id="owl_minCardinality" name="owl_minCardinality"></a>
<a id="owl_maxCardinality" name="owl_maxCardinality"></a>
Cardinality expressions with values limited to 0 or 1 are part of OWL Lite.
This permits the user to indicate 'at least one', 'no more than one',
and 'exactly one'.
Positive integer values other than 0 and 1 are permitted in OWL DL.
<tt>owl:maxCardinality</tt> can be used to specify an <em>upper</em> bound. 
<tt>owl:minCardinality</tt> can be used to specify a <em>lower</em> bound. 
In combination, the two can be used to limit the property's cardinality to 
a numeric interval.
</p>

<!-- 
<p>
MinCardinality defaults to 0. 
There is no default value for cardinality or maxCardinality. 
</p>
-->

<h3><a id="hasValue" name="hasValue">3.4.3. hasValue</a> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h3>

<p>
<a id="owl_hasValue" name="owl_hasValue"></a>
<tt>hasValue</tt> allows us to specify classes based on the
existence of <em>particular</em> property values. Hence,
an individual will be a member of such a class whenever at least <em>one</em>
of its property values is equal to the hasValue resource.
</p>

<pre>
&lt;owl:Class rdf:ID="Burgundy"&gt;
  ...
  &lt;rdfs:subClassOf&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#hasSugar" /&gt;
      &lt;owl:hasValue rdf:resource="#Dry" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/rdfs:subClassOf&gt;
&lt;/owl:Class&gt;
</pre>

<p>
Here we declare that all <tt>Burgundy</tt> wines are dry.  That is, their
<tt>hasSugar</tt> property must have at least one value that is equal
to <tt>Dry</tt>.
</p>

<p>
As for <tt>allValuesFrom</tt> and
<tt>someValuesFrom</tt>, this is a local restriction.  It holds for
<tt>hasSugar</tt> as applied to <tt>Burgundy</tt>.
</p>

<h1><a name="OntologyMapping">4. Ontology Mapping </a></h1>

<p>
In order for ontologies to have the maximum impact, they need to be
widely shared.  In order to minimize the intellectual effort involved
in developing an ontology they need to be re-used.  In the best of all
possible worlds they need to be composed.  For example, you might adopt
a date ontology from one source and a physical location ontology from
another and then extend the notion of location to include the time
period during which it holds.
</p>
<p>
It is important to realize that much of the effort of developing an
ontology is devoted to hooking together classes and properties in
ways that maximize implications.  We want simple assertions about
class membership to
have broad and useful implications.  This is the hardest part of
ontology development.  If you can find an existing ontology that has
already undergone extensive use and refinement, it makes sense to
adopt it.
</p>
<p>
It will be challenging to merge a collection of ontologies.  Tool
support will almost certainly be required to maintain consistency.
</p>

<h2><a id="equivalentClass1" name="equivalentClass1">
4.1. Equivalence between Classes and Properties<br />
<tt>equivalentClass</tt>, <tt>equivalentProperty</tt></a></h2>

<p>To tie together a set of component ontologies as part of a
third it is frequently useful to be able to indicate that a particular
class or property in one ontology is equivalent to a class or property
in a second
ontology.  This capability must be used with care.
If the combined ontologies are contradictory (all A's
are B's vs. all A's are not B's) there will be no extension (no
individuals and relations) that satisfies the resulting combination.
</p>


<p>
<a id="owl_equivalentClass" name="owl_equivalentClass"></a>
<a id="owl_sameClassAs" name="owl_sameClassAs"></a>
In the food ontology we want to link wine features in the descriptions
of dining courses back to the wine ontology.  One way to do this is by
defining a class in the food ontology (&amp;food;Wine) and then 
declaring it equivalent to an existing wine class in the wine ontology.
</p>
<pre>
&lt;owl:Class rdf:ID="Wine"&gt;
  &lt;owl:equivalentClass rdf:resource="&amp;vin;Wine"/&gt;
&lt;/owl:Class&gt;
</pre>
<p>
The property <tt>owl:equivalentClass</tt> is used to indicate that two classes have
precisely the same instances.  Note that in OWL DL, classes simply denote sets
of individuals, and are not individuals themselves.  In OWL Full, however, 
we can use <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_sameAs"><tt>owl:sameAs</tt></a> 
between two classes to indicate that
they are identical in every way.
</p>

<p>
Of course the example above is somewhat contrived, since we can always
use <tt>&amp;vin;Wine</tt> anywhere we would use <tt>#Wine</tt> and get
the same effect without redefinition.  A more likely use would be in a
case were we depend on two independently developed ontologies, and
note that they use the URI's <tt>O1:foo</tt> and <tt>O2:bar</tt> to
reference the same class.  <tt>owl:equivalentClass</tt> could be used to
collapse these together so that the entailments from the two
ontologies are combined.
</p>

<p>
We have already seen that class expressions can be the targets
of <tt>rdfs:subClassOf</tt> constructors.  They can also be the target of
<tt>owl:equivalentClass</tt>.  Again, this avoids the need to
contrive names for every class expression and provides a powerful
definitional capability based on satisfaction of a property.  
</p>
<pre>
&lt;owl:Class rdf:ID="TexasThings"&gt; 
  &lt;owl:equivalentClass&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#locatedIn" /&gt;
      &lt;owl:someValuesFrom rdf:resource="#TexasRegion" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/owl:equivalentClass&gt;
&lt;/owl:Class&gt;                                               <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>

<tt>TexasThings</tt> are <em>exactly</em> those things located in the
Texas region.  The difference between using <tt>owl:equivalentClass</tt> here
and using <tt>rdfs:subClassOf</tt> is the difference between a necessary
condition and a necessary and sufficient condition.  With
<tt>subClassOf</tt>, things that are located in Texas are not
necessarily <tt>TexasThings</tt>.  But, using <tt>owl:equivalentClass</tt>, if
something is located in Texas, then it must be in the class of
<tt>TexasThings</tt>.
</p>
<table class="propositions">
  <tbody>
<tr><th>Relation</th><th>Implications</th></tr>
<tr><td>subClassOf</td><td>TexasThings(x) implies locatedIn(x,y) and TexasRegion(y)</td></tr>
<tr><td>equivalentClass&nbsp;&nbsp;</td><td>TexasThings(x) implies
locatedIn(x,y) and TexasRegion(y)<br />locatedIn(x,y) and
TexasRegion(y) implies TexasThings(x)</td></tr>
  </tbody>
</table>

<p>
<a id="owl_equivalentProperty" name="owl_equivalentProperty"></a>
<a id="owl_samePropertyAs" name="owl_samePropertyAs"></a>
To tie together properties in a similar fashion, we use
<tt>owl:equivalentProperty</tt>.
</p>

<h2>
<a id="owl_sameAs" name="owl_sameAs"></a>
<a id="sameAs" name="sameAs">
4.2. Identity between Individuals<br />
<tt>sameAs</tt></a></h2>

<p>This mechanism is similar to that for classes, but declares two
individuals to be identical.  An example would be:
</p>
<pre>
&lt;Wine rdf:ID="MikesFavoriteWine"&gt; 
  &lt;owl:sameAs rdf:resource="#StGenevieveTexasWhite" /&gt; 
&lt;/Wine&gt;                                                 <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>
This example does not have great utility.  About all we learn from this is
that Mike likes an inexpensive local wine.  A more typical use of
<tt>sameAs</tt> would be to equate individuals defined in
different documents to one another, as part of unifying two ontologies.
</p>

<p>
This brings up an important point.  OWL does not have a 
<a id="term_uniqueName" name="term_uniqueName"></a><em>unique
name</em> assumption.  Just because two names are different does not
mean they refer to different individuals.  
</p>

<p>
In the example above, we <em>asserted</em> identity between two distinct
names.  But it is just as possible for this sort of identity to be
inferred.
Remember the implications that can be derived from a functional
property.  Given that <tt>hasMaker</tt> is functional, the following
is not necessarily a conflict.   
</p>
<pre>
&lt;owl:Thing rdf:about="#BancroftChardonnay"&gt;
  &lt;hasMaker rdf:resource="#Bancroft" /&gt;
  &lt;hasMaker rdf:resource="#Beringer" /&gt;
&lt;/owl:Thing&gt;                                            <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>
Unless this conflicts with other information in our ontology, it simply means
that <tt>Bancroft</tt> = <tt>Beringer</tt>.
</p>

<p>
Note that using <tt>sameAs</tt> to equate two classes
is <b>not</b> the same as equating them with <tt>equivalentClass</tt>; instead, it causes the 
the classes to be interpreted as individuals, and is therefore sufficient 
to categorize an ontology as OWL Full.
In OWL Full <tt>sameAs</tt> may be used to equate 
anything: a class and an individual, a property and a class, etc., and causes both
arguments to be interpreted as individuals.
</p>

<h2><a name="differentFrom">4.3. Different Individuals<br />
<tt>differentFrom</tt>, <tt>AllDifferent</tt></a></h2>

<p>
<a id="owl_differentFrom" name="owl_differentFrom"></a>
This mechanism provides the opposite effect from sameAs.
</p>
<pre>
&lt;WineSugar rdf:ID="Dry" /&gt;

&lt;WineSugar rdf:ID="Sweet"&gt;  
  &lt;owl:differentFrom rdf:resource="#Dry"/&gt;  
&lt;/WineSugar&gt; 

&lt;WineSugar rdf:ID="OffDry"&gt;
  &lt;owl:differentFrom rdf:resource="#Dry"/&gt; 
  &lt;owl:differentFrom rdf:resource="#Sweet"/&gt; 
&lt;/WineSugar&gt;
</pre> 

<p>
This is one way to assert that these three values are mutually distinct.
There will be cases where it is important to ensure such distinct
identities.  Without these assertions we could describe a wine that was
both <tt>Dry</tt> and <tt>Sweet</tt>.  We have
stated that the <tt>hasSugar</tt> property applied to a wine has no more than
one value.  If we erred, and asserted that a wine was both <tt>Dry</tt> and
<tt>Sweet</tt>, without the <tt>differentFrom</tt> elements above,
this would imply that <tt>Dry</tt> and <tt>Sweet</tt> are identical.
With the elements above, we would instead get a contradiction.
</p>

<p>
<a id="owl_AllDifferent" name="owl_AllDifferent"></a>
<a id="owl_distinctMembers" name="owl_distinctMembers"></a>
A more convenient mechanism exists to define a set of mutually
distinct individuals.  The following asserts that <tt>Red</tt>,
<tt>White</tt>, and <tt>Rose</tt> are pairwise distinct.
</p>
<pre>
&lt;owl:AllDifferent&gt;
  &lt;owl:distinctMembers rdf:parseType="Collection"&gt;
    &lt;vin:WineColor rdf:about="#Red" /&gt;
    &lt;vin:WineColor rdf:about="#White" /&gt;
    &lt;vin:WineColor rdf:about="#Rose" /&gt;
  &lt;/owl:distinctMembers&gt;
&lt;/owl:AllDifferent&gt;
</pre>
<p>Note that <tt>owl:distinctMembers</tt> can only be used 
in combination with <tt>owl:AllDifferent</tt>
</p>
<p>
In the wine ontology we provide an <tt>owl:AllDifferent</tt> assertion
for all of the <tt>WineDescriptor</tt>s.  We also state that 
the <tt>Winery</tt>s are all different.  If we wanted to add a new
winery in some other ontology and assert that it was disjoint from all
of those that have already been defined, we would need to cut and
paste the original <tt>owl:AllDifferent</tt> assertion and add the new
maker to the list.  There is not a simpler way to extend an
<tt>owl:AllDifferent</tt> collection in OWL DL.  In OWL Full, using
RDF triples and the rdf:List constructs, other approaches are possible.
</p>

<hr />

<h1><a name="ComplexClasses">5. Complex Classes</a>
 <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h1>
    
<p>
OWL provides additional constructors with which to form classes. These
constructors can be used to create so-called <em>class
expressions</em>. OWL supports the basic set operations, namely
union, intersection and complement.  These are named 
<tt>owl:unionOf</tt>, <tt>owl:intersectionOf</tt>, and <tt>owl:complementOf</tt>, 
respectively. Additionally, classes can be 
<a id="term_enumerated" name="term_enumerated"></a><em>enumerated</em>.  
Class extensions can be stated explicitly by means of the
<tt>oneOf</tt> constructor.  
And it is possible to assert that class extensions must be disjoint.
</p>

<p>
Note that Class expressions can be nested without requiring the creation
of names for every intermediate class.  
This allows the use of set operations to build up complex classes
from anonymous classes or classes with value restrictions.  
</p>


<h2><a id="SetOperators" name="SetOperators">5.1. Set Operators</a><br />
<tt>intersectionOf, unionOf, complementOf</tt>
</h2>

<p>
Remember that OWL class extensions are sets consisting of the individuals
that are members of the class. OWL provides the means to
manipulate class extensions using basic set operators.
</p>

<h3><a id="owl_intersectionOf" name="owl_intersectionOf">5.1.1. Intersection</a>
 <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[some uses of OWL DL]</a></h3>

<p>

The following examples demonstrate the use of the
<a id="term_intersection" name="term_intersection"></a><em>intersectionOf</em> construct.  
</p>
<pre>
&lt;owl:Class rdf:ID="WhiteWine"&gt;
  &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#Wine" /&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#hasColor" /&gt;
      &lt;owl:hasValue rdf:resource="#White" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/owl:intersectionOf&gt;
&lt;/owl:Class&gt;
</pre>
<p>
Classes constructed using the set operations are more like
definitions than anything we have seen to date. 
The members of the class are completely specified by
the set operation.
The construction above states that <tt>WhiteWine</tt> is <em>exactly</em> the
intersection of the class <tt>Wine</tt> and the set of things that are
white in color.  This means that if something is white and a wine,
then it is an instance of <tt>WhiteWine</tt>.  Without such a definition
we can know that white wines are wines and white, but not vice-versa.
This is an important tool for categorizing individuals.
(Note that 'rdf:parseType="Collection"' is a required syntactic element.)

</p>
<pre>
&lt;owl:Class rdf:about="#Burgundy"&gt;
  &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#Wine" /&gt;
    &lt;owl:Restriction&gt;
      &lt;owl:onProperty rdf:resource="#locatedIn" /&gt;
      &lt;owl:hasValue rdf:resource="#BourgogneRegion" /&gt;
    &lt;/owl:Restriction&gt;
  &lt;/owl:intersectionOf&gt;
&lt;/owl:Class&gt;
</pre>

<p>
Here we define <tt>Burgundy</tt> to include exactly those wines that have
at least one <tt>locatedIn</tt> relation to the Bourgogne Region.  
We could have declared a new class
<tt>ThingsFromBourgogneRegion</tt> and used it as a class in the
<tt>owl:intersectionOf</tt> construct.  Since we do not have any other
use for <tt>ThingsFromBourgogneRegion</tt>, the declaration above is
shorter, clearer and doesn't require the creation of a contrived name.
</p>

<pre>
&lt;owl:Class rdf:ID="WhiteBurgundy"&gt;
  &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#Burgundy" /&gt;
    &lt;owl:Class rdf:about="#WhiteWine" /&gt;
  &lt;/owl:intersectionOf&gt; 
&lt;/owl:Class&gt;
</pre>
<p>
Finally, the class <tt>WhiteBurgundy</tt> is exactly the intersection of 
white wines and Burgundies.  Burgundies in turn are grown in the
French region of Bourgogne and are dry wines.  Accordingly all
individual wines that meet these criteria are part of the class
extension of <tt>WhiteBurgundy</tt>.
</p>

<h3><a id="owl_unionOf" name="owl_unionOf">5.1.2. Union</a> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h3>

<p>

The following example demonstrates the use of the
<a id="term_union" name="term_union"></a><em>unionOf</em> construct. It is used exactly like the
<em>intersectionOf</em> construct:
</p>

<pre>
&lt;owl:Class rdf:ID="Fruit"&gt;
  &lt;owl:unionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#SweetFruit" /&gt;
    &lt;owl:Class rdf:about="#NonSweetFruit" /&gt;
  &lt;/owl:unionOf&gt;
&lt;/owl:Class&gt;
</pre> 

<p>
The class <tt>Fruit</tt> includes <em>both</em>
the extension of <tt>SweetFruit</tt> and the extension of 
<tt>NonSweetFruit</tt>. 
</p>

<p>
Note how completely different this union type construct is from the following.
</p>

<pre>
&lt;owl:Class rdf:ID="Fruit"&gt;
  &lt;rdfs:subClassOf rdf:resource="#SweetFruit" /&gt;
  &lt;rdfs:subClassOf rdf:resource="#NonSweetFruit" /&gt;
&lt;/owl:Class&gt;                                            <span class="red">&nbsp;&not;&nbsp;</span>
</pre> 

<p>
This says that the instances of <tt>Fruit</tt> are a subset of the
<em>intersection</em> of sweet and non-sweet fruit, which we would
expect to be the empty set.
</p>

<h3><a id="owl_complementOf" name="owl_complementOf">
5.1.3. Complement</a> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h3>

<p>
The <a id="term_complement" name="term_complement"></a><em>complementOf</em> construct selects all individuals from
the domain of discourse that do not belong to a certain
class. Usually this refers to a very large set of individuals:
</p>
<pre>
  &lt;owl:Class rdf:ID="ConsumableThing" /&gt;

  &lt;owl:Class rdf:ID="NonConsumableThing"&gt;
    &lt;owl:complementOf rdf:resource="#ConsumableThing" /&gt;
  &lt;/owl:Class&gt;
</pre>

<p>
The class of <tt>NonConsumableThing</tt> includes as its members
all individuals that do not belong to the extension
of <tt>ConsumableThing</tt>.  This set includes all
<tt>Wine</tt>s, <tt>Region</tt>s, etc.  It is literally the set
difference between <tt>owl:Thing</tt> and  <tt>ConsumableThing</tt>. 
Therefore, a typical usage pattern for
<em>complementOf</em> is in combination with other set
operators:
</p>
<pre>
&lt;owl:Class rdf:ID="NonFrenchWine"&gt;
  &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#Wine"/&gt;
    &lt;owl:Class&gt;
      &lt;owl:complementOf&gt;
        &lt;owl:Restriction&gt;
          &lt;owl:onProperty rdf:resource="#locatedIn" /&gt;
          &lt;owl:hasValue rdf:resource="#FrenchRegion" /&gt;
        &lt;/owl:Restriction&gt;
      &lt;/owl:complementOf&gt;
    &lt;/owl:Class&gt;
  &lt;/owl:intersectionOf&gt;
&lt;/owl:Class&gt;                                            <span class="red">&nbsp;&not;&nbsp;</span>
</pre> 

<p>
<!-- From Guide comments:
The example at the end is very complex because it uses the 
TransitiveProperty feature of locatedIn for warranting that whatever 
is declared to be in, say, Bourgogne, will also be locatedIn 
FrenchRegion. I could add a couple of sentences to explain it.
-->

This defines the class <tt>NonFrenchWine</tt> to be the
intersection of <tt>Wine</tt> with the set of all
things <em>not</em> located in France.
</p>

<h2><a name="EnumeratedClasses">5.2. Enumerated Classes</a><br />
<tt>oneOf</tt> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h2>

<p>
OWL provides the means to specify a class via a direct enumeration of its
members. This is done using the <em>oneOf</em> construct. Notably,
this definition completely specifies the class extension, so that no other
individuals can be declared to belong to the class.
</p>

<p>
<a id="owl_oneOf" name="owl_oneOf"></a>
The following defines a class <tt>WineColor</tt> whose
members are the individuals <tt>White</tt>, <tt>Rose</tt>, and
<tt>Red</tt>.
</p>

<pre>
&lt;owl:Class rdf:ID="WineColor"&gt;
  &lt;rdfs:subClassOf rdf:resource="#WineDescriptor"/&gt;
  &lt;owl:oneOf rdf:parseType="Collection"&gt;
    &lt;owl:Thing rdf:about="#White"/&gt;
    &lt;owl:Thing rdf:about="#Rose"/&gt;
    &lt;owl:Thing rdf:about="#Red"/&gt;
  &lt;/owl:oneOf&gt;
&lt;/owl:Class&gt;
</pre> 

<p>
The first thing to understand here is that no other individuals can be
a valid <tt>WineColor</tt> since the class has been defined by
enumeration.
</p>

<p>
Each element of the <tt>oneOf</tt> construct must be a validly declared
individual. An individual has to belong to some class. In the above
example, each individual was referenced by name.  We used
<tt>owl:Thing</tt> as a simple clich&eacute; to introduce the reference.
Alternatively, we could have referenced the elements of the set
according to their specific type, <tt>WineColor</tt>, by:
</p>

<pre>
&lt;owl:Class rdf:ID="WineColor"&gt;
  &lt;rdfs:subClassOf rdf:resource="#WineDescriptor"/&gt;
  &lt;owl:oneOf rdf:parseType="Collection"&gt;
    &lt;WineColor rdf:about="#White" /&gt;
    &lt;WineColor rdf:about="#Rose" /&gt;
    &lt;WineColor rdf:about="#Red" /&gt;
  &lt;/owl:oneOf&gt;
&lt;/owl:Class&gt;
</pre>

<p>
Other, more complex descriptions of individuals are also valid
elements of the <em>oneOf</em> construct, for example:
</p>

<pre>
&lt;WineColor rdf:about="#White"&gt;
  &lt;rdfs:label&gt;White&lt;/rdfs:label&gt;
&lt;/WineColor&gt;                                            <span class="red">&nbsp;&not;&nbsp;</span>
</pre>

<p>
For additional examples of the use of <tt>oneOf</tt>, see the 
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#EnumeratedDatatype">
Reference</a>.
</p>

<h2><a id="DisjointClasses" name="DisjointClasses">5.3. Disjoint Classes</a> <br />
<tt>disjointWith</tt> <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OWL_DL_tag">[OWL DL]</a></h2>

<p>
<a id="owl_disjointWith" name="owl_disjointWith"></a>
The disjointness of a set of classes can be expressed using the
<tt>owl:disjointWith</tt> constructor. It guarantees that an
individual that is a member of one class cannot simultaneously be an
instance of a specified other class.  
</p>

<pre>
&lt;owl:Class rdf:ID="Pasta"&gt;
  &lt;rdfs:subClassOf rdf:resource="#EdibleThing"/&gt;
  &lt;owl:disjointWith rdf:resource="#Meat"/&gt;
  &lt;owl:disjointWith rdf:resource="#Fowl"/&gt;
  &lt;owl:disjointWith rdf:resource="#Seafood"/&gt;
  &lt;owl:disjointWith rdf:resource="#Dessert"/&gt;
  &lt;owl:disjointWith rdf:resource="#Fruit"/&gt;
&lt;/owl:Class&gt;
</pre>

<p>
The <tt>Pasta</tt> example demonstrates multiple disjoint classes.
Note that this only asserts that <tt>Pasta</tt> is disjoint from all
of these other classes.  It does not assert, for example, that
<tt>Meat</tt> and <tt>Fruit</tt> are disjoint.  In order to assert
that a set of classes is mutually disjoint, there must be an
<tt>owl:disjointWith</tt> assertion for every pair.
</p>

<p>
A common requirement is to define
a class as the union of a set of mutually disjoint subclasses.
</p>
<pre>
&lt;owl:Class rdf:ID="SweetFruit"&gt;
  &lt;rdfs:subClassOf rdf:resource="#EdibleThing" /&gt;
&lt;/owl:Class&gt;

&lt;owl:Class rdf:ID="NonSweetFruit"&gt;
  &lt;rdfs:subClassOf rdf:resource="#EdibleThing" /&gt;
  &lt;owl:disjointWith rdf:resource="#SweetFruit" /&gt;
&lt;/owl:Class&gt;

&lt;owl:Class rdf:ID="Fruit"&gt;
  &lt;owl:unionOf rdf:parseType="Collection"&gt;
    &lt;owl:Class rdf:about="#SweetFruit" /&gt;
    &lt;owl:Class rdf:about="#NonSweetFruit" /&gt;
  &lt;/owl:unionOf&gt;
&lt;/owl:Class&gt;
</pre>

<p>
Here we define <tt>Fruit</tt> to be exactly the union of
<tt>SweetFruit</tt> and <tt>NonSweetFruit</tt>.  And we know that
these subclasses exactly partition <tt>Fruit</tt> into two distinct subclasses
because they are disjoint.  
As the number of mutually disjoint classes
grows, the number of disjointness assertions grows proportionally to
n<sup>2</sup>.  However, in the use cases we have seen, n is typically
small.
</p>
<p>
When n is large, alternate approaches can be used to avoid quadratic
growth in the number of assertions.  One such method is illustrated in
the
<a href="http://www.w3.org/TR/2004/REC-owl-test-20040210/byIssue#I5.21-002">
OWL test suite
</a>
</p>
<p>
The illustrated method works as follows.  We describe a parent class
whose elements have a property with cardinality equal to one.  That
is, each instance must have one and only one value for this property.
Then, for every subclass of the parent we require that its instances
must have a particular unique value for the property.  In which case
none of the distinct subclasses can have members in common.
</p>

<hr />

<h1><a id="OntologyVersioning" name="OntologyVersioning"></a>
<a id="term_version" name="term_version"></a>
6. Ontology Versioning</h1>

<p>
<a id="owl_priorVersion" name="owl_priorVersion"></a>
Ontologies are like software, they will be maintained and thus will change 
over time.  
Within an <tt>owl:Ontology</tt> element
(discussed <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OntologyHeaders">above</a>), it is possible to link to a previous
version of the ontology being defined.  The <tt>owl:priorVersion</tt> property
is intended to provide this link, and can be used to track the
version history of an ontology.
</p>
<pre>
&lt;owl:Ontology rdf:about=""&gt; 
  ...
  &lt;owl:priorVersion rdf:resource="http://www.w3.org/TR/2003/CR-owl-guide-20030818/wine"/&gt; 
  ...
&lt;/owl:Ontology&gt;
</pre>
<p>
The indicated ontology is a previous version of the one being defined.  
</p>

<p>
<a id="owl_backwardCompatibleWith" name="owl_backwardCompatibleWith"></a>
<a id="owl_incompatibleWith" name="owl_incompatibleWith"></a>
Ontology versions may not be compatible with each other.  For example, a 
prior version of an ontology may contain statements that contradict the current
version.    Within an <tt>owl:Ontology</tt> element, 
we use the tags <tt>owl:backwardCompatibleWith</tt>
and <tt>owl:incompatibleWith</tt> to indicate compatibility or the
lack thereof with previous ontology versions.  
If <tt>owl:backwardCompatibleWith</tt> is not declared, then
compatibility should not be assumed.   
<a id="owl_versionInfo" name="owl_versionInfo"></a>
In addition, <tt>owl:versionInfo</tt> 
provides a hook suitable for use by versioning systems.  As opposed to the previous three tags, 
the object of <tt>owl:versionInfo</tt> is a literal and the tag can be used 
to annotate classes and properties in addition to ontologies.
</p>
<p>
<a id="owl_DeprecatedClass" name="owl_DeprecatedClass"></a>
<a id="owl_DeprecatedProperty" name="owl_DeprecatedProperty"></a>
For many purposes, doing version tracking at the granularity of
an entire ontology is not enough.  Maintainers may wish to keep
version information for classes, properties, and individuals - and 
even that may not be sufficient.  The incremental nature of class expressions
in OWL implies that one ontology may add restrictions to a (named) class defined
in another ontology, and 
these additional restrictions themselves may require version information.
</p>
<p>
OWL Full provides the expressive power to make any sort of assertion about a class,
i.e. that it is an instance of another class, or that it (and not its instances) has
a property and a value for that property.  This framework can be used
to build an ontology of classes and properties for tracking version information.
The OWL namespace includes two pre-defined classes that can be used for this purpose:
<tt>owl:DeprecatedClass</tt>
and <tt>owl:DeprecatedProperty</tt>.
They are intended to indicate that the class or property will likely be changing in an
incompatible manner in a forthcoming release:
</p>
<pre>
...
  &lt;owl:DeprecatedClass rdf:ID="&amp;vin;JugWine" /&gt;
  &lt;owl:DeprecatedProperty rdf:ID="&amp;vin;hasSeeds" /&gt;
...                                                           <span class="red">&nbsp;&not;&nbsp;</span>
</pre>
<p>
It is important to note that <tt>owl:DeprecatedClass</tt>
and <tt>owl:DeprecatedProperty</tt>
have no additional semantics and it is up to tool
developers and OWL users to ensure they are used as intended.
</p>

<!--
<li>They should provide a useful starting point for defining a more
extensive ontology of versioning properties and classes.</li>

<li>Using these classes in an ontology makes it an OWL Full ontology.
However, users who need versioning and who wish their ontologies to
remain in OWL DL or OWL Lite can do so by separating these versioning
statements into another ontology that imports the one for which
versioning information is needed.</li> 
</ul>
-->

<hr />


<h1><a id="Usage" name="Usage">7. Usage Examples</a></h1>

<p>
Once an initial domain ontology is available, a 
large number of applications can be developed that exploit the
ontology.  In this section, we describe some
sample uses in the domain of wines.  

</p>

<h2><a id="WinePortal" name="WinePortal">7.1. Wine Portal</a></h2>

<p>
A number of sites exist today that call themselves wine portals.
Google for example, provides 152,000 matches for the query "wine
portal".  One of the top matches, a site called 
<a href="http://www.wine-portal.com/">"Wine-Portal.com"</a>,
provides access to a number of sites.  Many sites
claiming to be wine portals are mostly informational sites.  For
example, wine-portal.com's first featured site, called 'cork cuisine'
(<a href="http://www.corkcuisine.com/">www.corkcuisine.com/</a>),
provides information about matching
wines and foods, wines as gifts, etc.
</p>

<p>
Perusing any of the topic areas, one finds a collection of pages
containing information and sometimes services related to the topic.
For example, 'accessories and gifts' contains information about what to
look for when buying particular wine items and also contains a
significant number of online retailers.  Another top level area called
'shopping' has a subarea called 'wine shopping' from which a user can find
online (or 'street shopping') stores (categorized by country).
These two sites are just two of the many examples
today and are representative of the general notion of a wine portal providing
a collection of information and services connected to a particular topic
area.
</p>
<p>
When looking at these sites in some detail, it is not clear how much
they depend on ontologies today.  For example, viewing the source
for the html does not reveal evidence of ontological usage.  However,
it is clear that the sites could exploit ontologies had some wine ontologies
been available.
</p>
<p>
One simple use of ontologies in portal sites is for organization and
browsing.  The listing of categories above could be generated from
the top few levels of wine related classes.  Queries could exploit
wine ontologies to <i>retrieve</i> wine relevant information. 
If one did a search for a term contained in the ontology, the query could
be expanded with subclass information in order to find more relevant answers. 

Portals could be made to automatically update themselves with (candidate) information
in topic areas.  With very powerful reasoning 
capabilities they could even identify likely wine sales sites and
negotiate to include them as part of the portal.

</p>


<h2><a id="WineAgent" name="WineAgent">7.2. Wine Agent</a></h2>

<p>
We have started a <a href="http://www.ksl.stanford.edu/people/dlm/webont/wineAgent/">
wine agent</a> for expository purposes. In our initial design,
the wine agent's goal is to recommend wines to accompany meal courses.
This application exploits the ontology used as the basis of this guide. 
This wine ontology is available in the DAML ontology library and is entitled
<a href="http://www.daml.org/ontologies/76">wines.</a>
</p>

<p>A personalized wine agent can provide a number of services for a human.
<br />The agent may be used to recommend wines given a set of constraints
(such as a meal being served),  the agent may find information about
a particular wine or a particular class of wines, it may look for appropriate
accessories for a wine (such as a particular kind of glass suited for that
wine varietal, etc.).
</p>

<p>Below, we describe an example in a simple prototype system that is being
written as a student project.
</p>

<p>Consider the following scenario:<br /><br />
Someone is planning a dinner party and at least one of the guests is
wine knowledgeable.  The host would like to serve wine that is well
matched to the course(s) on the menu.  The host would also like to
appear knowledgeable about the wines served at the event.  The host
would also like to have appropriate accessories at the dinner. The host
may have decided to serve a special tomato based pasta sauce with fresh
pasta as the main course.
</p>

<p>In order to serve wines appropriate to the meal, the host needs information
concerning wine and food pairings.  In order to appear knowledgeable
about wines, the host would benefit from having access to wine information
relevant to the event.  In order to have appropriate wine accessories,
the host would need to have information about what accessories are relevant
to the situation (and are within the host's price range).
</p>

<p>
With a background wine ontology, given a description of a meal, a wine
agent can suggest the type of wine to serve with the meal.  The wine
agent may suggest a zinfandel as the varietal of choice for the meal. 
Additionally, given a background ontology, the wine agent may suggest a
particular zinfandel, possibly Marietta Zinfandel. Given the information
that the wine should be a zinfandel, a wine agent may look for a place
to acquire either a selection of zinfandels or it may look for a particular
zinfandel wine, such as Marietta.  Given a background ontology containing
appropriate sources for wine purchases (possibly filtered by the location
of the host and the location of the wine seller), the wine agent could
go to a site such as <a href="http://www.wine.com/">wine.com</a> and do
a search for 'zinfandels' returning a listing
of zinfandels for sale on that site.  The wine agent could attempt
to find <a href="http://www.b-21.com/marietta/">Marietta</a> <a href="http://www.mariettacellars.com/welcome.html">Zinfandel</a>
either from the winery itself or from other resellers.  It could,
for example, find (by a search on Google or a structured search of selected
Web sites) that winelibrary.com has a sale on Marietta Zinfandel 1999 vintage
for a discounted price of $13.99.    The wine agent could
use additional filtering information such as price ranges provided either
by the consumer or as suggestions based on varietal.
</p>

<p>
The wine agent may now attempt to provide information concerning
zinfandel in general or Marietta Zinfandel in particular.  It could
use a background ontology of wine sites to find information about
particular wines.  For example, the winery <a href="http://www.mariettacellars.com/welcome.html">description</a> of
their most recent Zinfandel may be of use.  
Additionally reviews from respected sources such as the <a
href="http://www.winespectator.com/Wine/Home">Wine Spectator</a> may
be of use.  If no review of Marietta Zinfandel is available on a
favorite wine review site, it may be useful to look for related
information such as reviews on zinfandels from the same region, in
this case zinfandels from Sonoma County, California.
</p>

<p>
General background information may also be of use.  The host may
also want to do some reading and may be interested in books on wine in
general or zinfandels in particular.  For example, the host may be
interested in the books that Amazon.com has for <a href="http://www.amazon.com/exec/obidos/search-handle-url/index=books&amp;field-keywords=zinfandel&amp;search-type=ss&amp;bq=1/103-2905386-5649420">sale</a>
on zinfandel.   The host may also be interested in information
concerning wines from the same region, and thus may be interested in Sonoma
zinfandels.  A wine agent may have typical background information
available that is related to its main knowledge areas.  For example,
this wine agent is concerned with matching foods and wines, so it may have
both free and purchasable information on this topic such as the Wine Spectator's
article on <a href="http://www.winespectator.com/Wine/Wine_Basics/Wine_Basics_Template/0,1199,17,00.html">matching
food and wine</a>.
</p>

<p>
The dinner host  may also want to acquire appropriate wine accessories
prior to the event.  Wine is served in wine glasses and different
wine varietals are best served in different kinds of glasses.  For
example, if the host has chosen a meal course  for which a zinfandel
is appropriate, the host may want to know that <a href="http://www.riedelcrystal.com/index.htm">Riedel</a>
is a well-known manufacturer of wine glassware.  The host may also
want to be linked to the Wine Enthusiast (a well respected supplier of
wine merchandise) and be told that the Wine Enthusiast has <a href="http://www.wineenthusiast.com/shopping/prod_detail/main.asp?cat=GW&amp;catID=2&amp;sl=0&amp;productID=4099&amp;uid=8E539ACF-42AF-4EE4-BB3E-5BB42C28A8BC">Riedel's
Vinum Zinfandel glass</a> for sale as a set of 4 for $63.95 (with a discount
to $59.95 if you buy two sets of 4 glasses).   The host may also
be interested to know that Amazon.com has <a href="http://www.amazon.com/exec/obidos/tg/detail/-/B00006E9SS/qid=1033070213/sr=8-2/ref=sr_8_2/103-2905386-5649420?v=glance&amp;s=home-garden&amp;n=507846">Reidel's
Sommelier Zinfandel single stem glass</a> available for $49.99 (and claims
a list price of $65.00).    Amazon also has the same Vinum
glass for sale in sets of 6 (instead of 4 on the wine enthusiast) for $79.99
(and claims a list price of $119.40).  A wine agent could provide
a comparison listing of glassware that is matched to the meal (i.e., is
appropriate to be used to serve zinfandel) and then is compared by price
or other criteria chosen from a list of properties in the ontology.
</p>

<p>
The dinner host may want to consider other wine accessories.  From
the ontology, we know that corkscrews are wine accessories.  The background
ontology may encode subclasses of corkscrews or such information could
be found from relevant wine sites as well.     The
Wine Enthusiast has a set of <a href="http://www.wineenthusiast.com/content/gateway/gateway.asp?cat=CS&amp;uid=8E539ACF-42AF-4EE4-BB3E-5BB42C28A8BC">corkscrews</a>
they <a href="http://www.wineenthusiast.com/templates/recommend.asp?cat=EE&amp;uid=8E539ACF-42AF-4EE4-BB3E-5BB42C28A8BC">recommend</a>
(with descriptions of the types and price ranges).  They also distinguish
corkscrews by type (level, waiter, stationary, twist, and pump) and the
dinner host may want to get information about those styles.
</p>

<p>
The wine agent may be taken to many levels of sophistication depending
upon background ontology knowledge of the domain and information and services
sites.    In this example, we only exploited information
concerning wines, varietal type, food and wine combinations, some wine
accessories and their related properties.  We could of course expand
this to include more information and more constraints by the customer.
</p> 

<p>An evolving example of this wine agent is <a href="http://www.ksl.stanford.edu/people/dlm/webont/wineAgent/">available.</a>
</p>

<hr />

<h1><a id="Acknowledgements" name="Acknowledgements"></a>
Acknowledgements
</h1>

    <p>
      This document is the result of extensive discussions within
      the <a href="http://www.w3.org/2001/sw/WebOnt/">Web Ontology
      Working Group</a> as a whole. The participants in this
      Working Group included: Yasser alSafadi, Jean-Fran&#231;ois
      Baget, James Barnette, Sean Bechhofer, Jonathan Borden,
      Frederik Brysse, Stephen Buswell, Jeremy Carroll, Dan
      Connolly, Peter Crowther, Jonathan Dale, Jos De Roo, David De
      Roure, Mike Dean, Larry Eshelman, J&#233;r&#244;me Euzenat,
      Tim Finin, Nicholas Gibbins, Sandro Hawke, Patrick Hayes,
      Jeff Heflin, Ziv Hellman, James Hendler, Bernard Horan,
      Masahiro Hori, Ian Horrocks, Jane Hunter, Francesco
      Iannuzzelli, R&#252;diger Klein, Natasha Kravtsova, Ora
      Lassila, Massimo Marchiori, Deborah McGuinness, Enrico Motta,
      Leo Obrst, Mehrdad Omidvari, Martin Pike, Marwan Sabbouh,
      Guus Schreiber, Noboru Shimizu, Michael Sintek, Michael K.
      Smith, John Stanton, Lynn Andrea Stein, Herman ter Horst,
      David Trastour, Frank van Harmelen, Bernard Vatant, Raphael
      Volz, Evan Wallace, Christopher Welty, Charles White, and
      John Yanosy.
    </p>

<p> 
Some critical early text on complex restrictions was written by 
<a href="http://www.aifb.uni-karlsruhe.de/WBS/rvo/">Raphael Volz</a>, 
Forschungszentrum Informatik (FZI).
Substantial insight was provided by the 
<a href="http://www.w3.org/TR/daml+oil-walkthru/"><em>DAML+OIL Walkthru</em></a>. 
Jeremy Carroll, Jerome Euzenat, Jeff Heflin, Kevin Page and 
Peter F. Patel-Schneider provided extensive reviews. 
At the WG Face to Face, 8 October 2002, Stephen Buswell, 
Ruediger Klein, Enrico Motta, and Evan Wallace provided a detailed review of the 
ontology resulting in substantial changes. 
At the WG Face to Face, 10 January 2003, Jonathan Dale, Bernard Horan, 
Guus Schreiber, and Jeff Heflin provided detailed reviews of the 
Guide resulting in changes.
The 
<a href="http://lists.w3.org/Archives/Public/public-webont-comments/">
public reviews
</a>
provided numerous helpful suggestions and corrections.
</p>

<!--
<h1><a id="Notes" name="Notes">Notes</a></h1>

<dl>
  <dt><a id="Note-1" name="Note-1"></a>Note 1</dt>
  <dd>Text.</dd>

</dl>

<hr />
-->

<hr />

<h1><a id="Glossary" name="Glossary"></a>
<a id="OWLGlossary" name="OWLGlossary">OWL Glossary</a></h1>

<dl>

<dt>Attribute</dt><dd>as in XML</dd>
<dt>Class Definition</dt><dd>informal term for an owl:Class element</dd>
<dt>Class Description</dt><dd>describes an OWL class, either by a class name or
by specifying a class extension of an unnamed anonymous class
</dd>
<dt>Class name</dt><dd>informal term for an owl:Class rdf:ID attribute value.</dd>
<dt>Class</dt><dd>as in RDF</dd>
<dt>Component</dt><dd>for parts of a definition e.g. the arguments to intersection-of in a class definition</dd>
<dt>Concept</dt><dd>informal term for the abstractions "in the world" that ontologies describe</dd>
<dt>Constraint</dt><dd>informal term for discussing the effect of a restriction</dd>
<dt>Data-valued Property</dt><dd>alternative term for DataType Property</dd>
<dt>Datatype Property</dt><dd>an OWL property that relates individuals to data values</dd>
<dt>Datatype</dt><dd>an RDFS datatype, almost always one of the built-in non-list XML Schema datatypes </dd>
<dt>Element</dt><dd>(1) as in XML</dd><dd>(2) an element of a set</dd>
<dt>Entity</dt><dd>as in XML</dd>
<dt>Imports Closure</dt><dd>the information in an ontology document, plus the information in the imports closure of ontology documents that are imported by the document</dd>
<dt>Individual-valued Property</dt><dd>alternative term for Object Property </dd>
<dt>Individual</dt><dd>an instance of an OWL class, i.e., a resource that belongs to the class extension of an OWL class</dd>
<dt>Instance Of</dt><dd>the relation between an individual and a class</dd>
<dt>Instance</dt><dd>a member of the class extension of an OWL class</dd>
<dt>Name</dt><dd>as in XML Namespaces</dd>
<dt>Named Class</dt><dd>an OWL class with an associated identifier</dd>
<dt>Node</dt><dd>as in RDF Graphs</dd>
<dt>OWL Class</dt><dd>an RDFS class that belongs to the class extension of owl:Class</dd>
<dt>Object Property</dt><dd>an OWL property that relates individuals to other individuals</dd>
<dt>Object</dt><dd>(1) the object of an RDF triple</dd> <dd>(2) an alternative term for individual (used for historical reasons)</dd>
<dt>Ontology Document</dt><dd>a Web document that contains an ontology, generally indicated by the presence of an owl:Ontology element in the document</dd>
<dt>Ontology</dt><dd>(1) collection of information, generally including information about classes and properties</dd><dd>(2) the information contained in an ontology document </dd>
<dt>Property Definition</dt><dd>informal term for an
owl:ObjectProperty element and or owl:DatatypeProperty element </dd>
<dt>Resource</dt><dd>an element of the RDF domain of discourse</dd>
<dt>Restriction, global</dt><dd>reserved for discussions of the <tt>domain</tt> and <tt>range</tt> of properties</dd>
<dt>Restriction, local</dt><dd>[see above]</dd>
<dt>Restriction</dt><dd>usually a piece of a class expression, a statement that expresses a constraint, local by default</dd>
<dt>Set</dt><dd>a mathematical set</dd>
<dt>Statement</dt><dd>as in RDF Graphs</dd>
<dt>Type</dt><dd>as in RDF (rdf:type)</dd>
<dt>URI reference</dt><dd>as in RDF </dd>
<dt>Unnamed Class</dt><dd>an OWL class without an associated identifier, normally components of restrictions.</dd>
<dt>Vocabulary</dt><dd>a set of URI references</dd>

</dl>

<br /><br />

<hr />

<h1><a id="TermIndexAndCrossReference" name="TermIndexAndCrossReference">
Term Index and Cross Reference</a></h1>

<h2><a id="TermIndex" name="TermIndex">Term Index</a></h2>

<table width="50%">
  <tbody>
<tr><th>Term</th><th>Section</th></tr>

<tr><td class="index">anonymous class</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_anonymousClass">3.2.1. </a></td></tr>
<tr><td class="index">class</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_class">3.1.3. </a></td></tr>
<tr><td class="index">cardinality</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_cardinality">3.4.2. </a></td></tr>
<tr><td class="index">complement</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_complement">5.1.3. </a></td></tr>
<tr><td class="index">datatype</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_datatype">3.2.1. </a></td></tr>
<tr><td class="index">datatype property</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_datatypeproperties">3.2.1. </a></td></tr>
<tr><td class="index">domain</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_domain">3.2.1. </a></td></tr>
<tr><td class="index">entailed</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_entailed">1. </a></td></tr>
<tr><td class="index">enumerated</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_enumerated">5. </a></td></tr>
<tr><td class="index">extension</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_extension">3.1. </a></td></tr>
<tr><td class="index">instance of</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_instance">3.1.3. </a></td></tr>
<tr><td class="index">intersectionOf</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_intersection">5.1.1. </a></td></tr>
<tr><td class="index">imports</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_import">2.2. </a></td></tr>
<tr><td class="index">individual</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_individual">3.1.3. </a></td></tr>
<tr><td class="index">instance</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_instanceOf">3.1.3. </a></td></tr>
<tr><td class="index">monotonic</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_monotonic">2. </a></td></tr>
<tr><td class="index">object properties</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_objectproperties">3.2.1. </a></td></tr>
<tr><td class="index">ontology</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_ontology">1. </a></td></tr>
<tr><td class="index">open world</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_openworld">2. </a></td></tr>
<tr><td class="index">OWL DL</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_OWLDL">1.1. </a></td></tr>
<tr><td class="index">OWL Full</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_OWLFull">1.1. </a></td></tr>
<tr><td class="index">OWL Lite</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_OWLLite">1.1. </a></td></tr>
<tr><td class="index">property</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_Properties">3.2.1. </a></td></tr>
<tr><td class="index">range</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_range">3.2.1. </a></td></tr>

<tr><td class="index">restriction class</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_restriction_class">3.4.1. </a></td></tr>

<tr><td class="index">union</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_union">5.1.2. </a></td></tr>
<tr><td class="index">unique names</td>
    <td class="index"><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#term_uniqueName">4.2. </a></td></tr>
  </tbody>
</table>
<br /><br />

<h2><a id="CrossReference" name="CrossReference">
Guide, Reference and Semantics Cross Reference</a>
</h2>

<table>
  <tbody>
<tr><th>OWL Guide</th><th>OWL Reference</th><th>OWL Semantics</th></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_AllDifferent">owl:AllDifferent / 4.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#AllDifferent-def">owl:AllDifferent</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#owl_AllDifferent_rdf">owl:AllDifferent</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_allValuesFrom">owl:allValuesFrom / 3.4.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#allValuesFrom-def">owl:allValuesFrom</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_allValuesFrom_semantics">owl:allValuesFrom</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_AnnotationProperty">owl:AnnotationProperty / 2.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#AnnotationProperty-def">owl:AnnotationProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_AnnotationProperty_semantics">owl:AnnotationProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_backwardCompatibleWith">owl:backwardCompatibleWith / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#backwardCompatibleWith-def">owl:backwardCompatibleWith</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#owl_backwardCompatibleWith_mapping">owl:backwardCompatibleWith</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_cardinality">owl:cardinality / 3.4.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#cardinality-def">owl:cardinality</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_cardinality_semantics">owl:cardinality</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Class">owl:Class / 3.1.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#Class-def">owl:Class</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_Class_semantics">owl:Class</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_complementOf">owl:complementOf / 5.1.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#complementOf-def">owl:complementOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_complementOf_semantics">owl:complementOf</a></td></tr>

<tr>
<td class="index">&nbsp;</td>
<td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#EnumeratedDatatype">owl:DataRange</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_DataRange_semantics">owl:DataRange</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_DatatypeProperty">owl:DatatypeProperty / 3.2.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#DatatypeProperty-def">owl:DatatypeProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_DatatypeProperty_semantics">owl:DatatypeProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_DeprecatedClass">owl:DeprecatedClass / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#DeprecatedClass-def">owl:DeprecatedClass</a></td><td class="index">
&nbsp;</td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_DeprecatedProperty">owl:DeprecatedProperty / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#DeprecatedProperty-def">owl:DeprecatedProperty</a></td><td class="index">
&nbsp;</td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_differentFrom">owl:differentFrom / 4.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#differentFrom-def">owl:differentFrom</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_differentFrom_semantics">owl:differentFrom</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_disjointWith">owl:disjointWith / 5.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#disjointWith-def">owl:disjointWith</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_disjointWith_semantics">owl:disjointWith</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_distinctMembers">owl:distinctMembers / 4.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#distinctMembers-def">owl:distinctMembers</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#owl_distinctMembers_rdf">owl:distinctMembers</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_equivalentClass">owl:equivalentClass / 4.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#equivalentClass-def">owl:equivalentClass</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_equivalentClass_semantics">owl:equivalentClass</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_equivalentProperty">owl:equivalentProperty / 4.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#equivalentProperty-def">owl:equivalentProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_equivalentProperty_semantics">owl:equivalentProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_FunctionalProperty">owl:FunctionalProperty / 3.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#FunctionalProperty-def">owl:FunctionalProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_FunctionalProperty_semantics">owl:FunctionalProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_hasValue">owl:hasValue / 3.4.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#hasValue-def">owl:hasValue</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_hasValue_semantics">owl:hasValue</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_imports">owl:imports / 2.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#imports-def">owl:imports</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_imports_semantics">owl:imports</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_incompatibleWith">owl:incompatibleWith / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#incompatibleWith-def">owl:incompatibleWith</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#owl_incompatibleWith_mapping">owl:incompatibleWith</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_intersectionOf">owl:intersectionOf / 5.1.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#intersectionOf-def">owl:intersectionOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_intersectionOf_semantics">owl:intersectionOf</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_InverseFunctionalProperty">owl:InverseFunctionalProperty / 3.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#InverseFunctionalProperty-def">owl:InverseFunctionalProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_InverseFunctionalProperty_semantics">owl:InverseFunctionalProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_inverseOf">owl:inverseOf / 3.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#inverseOf-def">owl:inverseOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_inverseOf_semantics">owl:inverseOf</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_maxCardinality">owl:maxCardinality / 3.4.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#maxCardinality-def">owl:maxCardinality</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_maxCardinality_semantics">owl:maxCardinality</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_minCardinality">owl:minCardinality / 3.4.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#minCardinality-def">owl:minCardinality</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_minCardinality_semantics">owl:minCardinality</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Nothing">owl:Nothing / 3.1.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#Nothing-def">owl:Nothing</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_Nothing_semantics">owl:Nothing</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_ObjectProperty">owl:ObjectProperty / 3.2.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#ObjectProperty-def">owl:ObjectProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_ObjectProperty_semantics">owl:ObjectProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_oneOf">owl:oneOf / 5.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#oneOf-def">owl:oneOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_oneOf_semantics">owl:oneOf</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_onProperty">owl:onProperty / 3.4. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#onProperty-def">owl:onProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_onProperty_semantics">owl:onProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Ontology">owl:Ontology / 2.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#Ontology-def">owl:Ontology</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_Ontology_semantics">owl:Ontology</a></td></tr>

<tr><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#OntologyProperty-def">owl:OntologyProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_OntologyProperty_semantics">owl:OntologyProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_priorVersion">owl:priorVersion / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#priorVersion-def">owl:priorVersion</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#owl_priorVersion_mapping">owl:priorVersion</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Restriction">owl:Restriction / 3.4. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#Restriction-def">owl:Restriction</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_Restriction_semantics">owl:Restriction</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_sameAs">owl:sameAs / 4.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#sameAs-def">owl:sameAs</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_sameAs_semantics">owl:sameAs</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_someValuesFrom">owl:someValuesFrom / 3.4.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#someValuesFrom-def">owl:someValuesFrom</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_someValuesFrom_semantics">owl:someValuesFrom</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_SymmetricProperty">owl:SymmetricProperty / 3.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#SymmetricProperty-def">owl:SymmetricProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_SymmetricProperty_semantics">owl:SymmetricProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_Thing">owl:Thing / 3.1.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#Thing-def">owl:Thing</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_Thing_semantics">owl:Thing</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_TransitiveProperty">owl:TransitiveProperty / 3.3. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#TransitiveProperty-def">owl:TransitiveProperty</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_TransitiveProperty_semantics">owl:TransitiveProperty</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_unionOf">owl:unionOf / 5.1.2. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#unionOf-def">owl:unionOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#owl_unionOf_semantics">owl:unionOf</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#owl_versionInfo">owl:versionInfo / 6. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#versionInfo-def">owl:versionInfo</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#owl_versionInfo_mapping">owl:versionInfo</a></td></tr>

<tr><td class="index">
&nbsp;</td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#rdf_List_rdf">rdf:List</a></td></tr>

<tr><td class="index">
&nbsp;</td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#rdf_nil_rdf">rdf:nil</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdf_type">rdf:type</a></td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#rdf_type_semantics">rdf:type</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_comment">rdfs:comment / 2.2. </a></td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#rdfs_comment_mapping">rdfs:comment</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_Datatype">rdfs:Datatype / 3.2.2. </a></td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#rdfs_Datatype_rdf">rdfs:Datatype</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_domain">rdfs:domain / 3.2.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#domain-def">rdfs:domain</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#rdfs_domain_semantics">rdfs:domain</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_label">rdfs:label / 3.1.1. </a></td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/mapping.html#rdfs_label_mapping">rdfs:label</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_Literal">rdfs:Literal / 3.3. </a></td><td class="index">
&nbsp;</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#rdfs_Literal_rdf">rdfs:Literal</a></td></tr>

<!--
<tr><td class="index">
rdf:Property</td><td class="index">
rdf:Property</td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html#owl_Property_rdf">rdf:Property</a></td></tr>
-->
<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_range">rdfs:range / 3.2.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#range-def">rdfs:range</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#rdfs_range_semantics">rdfs:range</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_subClassOf">rdfs:subClassOf / 3.1.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#subClassOf-def">rdfs:subClassOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#rdfs_subClassOf_semantics">rdfs:subClassOf</a></td></tr>

<tr><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#rdfs_subPropertyOf">rdfs:subPropertyOf / 3.2.1. </a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/#subPropertyOf-def">rdfs:subPropertyOf</a></td><td class="index">
<a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#rdfs_subPropertyOf_semantics">rdfs:subPropertyOf</a></td></tr>
  </tbody>
</table>

<hr />

<h1><a name="References">References</a></h1>
  
<h2><a name="RelatedOWL">OWL</a></h2>

<dl>
  <dt><a id="FormalModel" name="FormalModel">[OWL Semantics and Abstract Syntax]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-owl-semantics-20040210/">
     <cite>OWL Web Ontology Language Semantics and Abstract Syntax</cite>
   </a>, 
   Peter F. Patel-Schneider, Patrick Hayes, and Ian Horrocks, Editors.
   W3C Recommendation, 10 February 2004,<br />
   http://www.w3.org/TR/2004/REC-owl-semantics-20040210/.<br />
   <a href="http://www.w3.org/TR/owl-semantics/">Latest version</a>
   available at http://www.w3.org/TR/owl-semantics/.
 </dd>

  <dt><a id="FeatureList" name="FeatureList">[OWL Overview]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-owl-features-20040210/">
      <cite>OWL Web Ontology Language Overview</cite>
    </a>, 
    Deborah L. McGuinness and Frank van Harmelen, Editors.
    W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-owl-features-20040210/. 
    <br />
    <a href="http://www.w3.org/TR/owl-features/">Latest version</a>
    available at http://www.w3.org/TR/owl-features/.
    <br />
  </dd> 

  <dt><a name="Reference" id="Reference">[OWL Reference]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-owl-ref-20040210/">
      <cite>OWL Web Ontology Language Reference</cite>
    </a>,  
    Mike Dean and Guus Schreiber, Editors.
    W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-owl-ref-20040210/.<br />
    <a href="http://www.w3.org/TR/owl-ref/">Latest version</a>
    available at http://www.w3.org/TR/owl-ref/.
    <br />
  </dd> 

  <dt><a id="Requirements" name="Requirements">[OWL Requirements]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-webont-req-20040210/">
    <cite>OWL Web Ontology Language Use Cases and Requirements</cite>
    </a>,
    Jeff Heflin, Editor.
    W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-webont-req-20040210/.<br />
    <a href="http://www.w3.org/TR/webont-req/">Latest version</a>
    available at http://www.w3.org/TR/webont-req/.
    <br /> 
  </dd> 

  <dt><a id="TestCases" name="TestCases">[OWL Test Cases]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-owl-test-20040210/">
      <cite>OWL Web Ontology Language Test Cases</cite>
    </a>, 
    Jeremy J. Carroll and Jos De Roo, Editors.
    W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-owl-test-20040210/.<br />
    <a href="http://www.w3.org/TR/owl-test/">Latest version</a>
    available at http://www.w3.org/TR/owl-test/.
  </dd>

</dl>

<h2><a name="RelatedStandards">Related W3C Standards</a></h2>
    
<dl>
 
  <dt><a id="RDF1" name="RDF1">[RDF]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/">
      <cite>Resource Description Framework (RDF) Model and Syntax Specification</cite>
    </a>, 
    Ora Lassila, Ralph R. Swick, Editors.
    World Wide Web Consortium Recommendation, 1999, <br />
    http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/.<br />
    <a href="http://www.w3.org/TR/REC-rdf-syntax/">Latest version</a>
    available at http://www.w3.org/TR/REC-rdf-syntax/.
  </dd>
 
  <dt>
    <a id="RDFS" name="RDFS">[RDFS]</a>
  </dt>
  <dd>
      <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210/">
        <cite>RDF Vocabulary Description Language 1.0: RDF Schema</cite>
      </a>,
      Dan Brickley and R.V. Guha, Editors.
      W3C Recommendation, 10 February 2004,<br />
      http://www.w3.org/TR/2004/REC-rdf-schema-20040210/ .<br />
      <a href="http://www.w3.org/TR/rdf-schema/">Latest version</a>
      available at http://www.w3.org/TR/rdf-schema/.
    </dd>

    <dt><a id="ref-rdf-concepts" name="ref-rdf-concepts">[RDF Concepts]</a></dt>
    <dd><cite>
      <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/">
      Resource Description Framework (RDF):  Concepts and Abstract Syntax</a></cite>,
      Graham Klyne and Jeremy J. Carroll, Editors.
      W3C Recommendation, 10 February 2004,<br />
      http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/.<br />
      <a href="http://www.w3.org/TR/rdf-concepts/">Latest version</a>
      available at http://www.w3.org/TR/rdf-concepts/.
    </dd>

  <dt><a id="RDFSemantics" name="RDFSemantics">[RDF Semantics]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-rdf-mt-20040210/">
      <cite>RDF Semantics</cite>
    </a>,
    Patrick Hayes, Editor.
W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-rdf-mt-20040210/. <br />
    <a href="http://www.w3.org/TR/rdf-mt/">Latest version</a>
    available at http://www.w3.org/TR/rdf-mt/.

</dd>
 
  <dt><a id="RDFSyntax" name="RDFSyntax">[RDF Syntax]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/">
      <cite>RDF/XML Syntax Specification (Revised)</cite>
    </a>,
    Dave Beckett, Editor.
    W3C Recommendation, 10 February 2004,<br />
    http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/.<br />
    <a href="http://www.w3.org/TR/rdf-syntax-grammar/">Latest version</a>
    available at http://www.w3.org/TR/rdf-syntax-grammar.
  </dd>


  <dt><a id="URI1" name="URI1">[URI]</a></dt>
  <dd>
    <a href="http://www.ietf.org/rfc/rfc2396.txt">
      <cite>Uniform Resource Identifiers (URI): Generic Syntax</cite>
    </a>,
    T. Berners-Lee, R. Fielding, and L. Masinter,
    IETF Draft Standard August, 1998 (RFC 2396).
  </dd>

  <dt><a id="XMLBase" name="XMLBase">[XML Base]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/xmlbase/">XML Base</a>,
    Jonathan Marsh, Editor. W3C Recommendation, 27 June 2001,<br />
    http://www.w3.org/TR/2001/REC-xmlbase-20010627/.<br />
    <a href="http://www.w3.org/TR/xmlbase/">Latest version</a>
    available at http://www.w3.org/TR/xmlbase/.
  </dd>

  <dt>
  <a id="XMLNS" name="XMLNS">[XML Namespaces]</a></dt>
  <dd>
    <a href="http://www.w3.org/TR/1999/REC-xml-names-19990114/"> 
      <cite>Namespaces in XML</cite>
    </a>,
    Tim Bray, Dave Hollander, Andrew Layman, Editors.
    W3C Recommendation, Jan 1999, <br />
    http://www.w3.org/TR/1999/REC-xml-names-19990114/.<br />
    <a href="http://www.w3.org/TR/REC-xml-names/">Latest version</a>
    available at http://www.w3.org/TR/REC-xml-names.
  </dd>

  <dt>
    <a id="XML1" name="XML1">[XML]</a>
  </dt>
  <dd>
    <a href="http://www.w3.org/TR/1998/REC-xml-19980210">
      <cite>Extensible Markup Language (XML) 1.0</cite>
    </a>,
    Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, Editors.
    W3C Recommendation, 10 February 1998,<br />
    http://www.w3.org/TR/1998/REC-xml-19980210.<br />
    <a href="http://www.w3.org/TR/REC-xml">Latest version</a>
    available at http://www.w3.org/TR/REC-xml.
  </dd>
  
  <dt>
    <a id="XMLSCHEMA-1" name="XMLSCHEMA-2">[XML Schema 1]</a>
  </dt>
  <dd>
    <a href="http://www.w3.org/TR/xmlschema-1/">
      <cite>XML Schema Part 1: Structures</cite></a>,
      Henry S. Thompson, David Beech, Murray Maloney, and Noah Mendelsohn, Editors.
      W3C Recommendation, 2 May 2001, <br />
      http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/.<br />
      <a href="http://www.w3.org/TR/xmlschema-1/">Latest version</a> available at 
      http://www.w3.org/TR/xmlschema-1/.
  </dd>
  <dt>
    <a id="XMLSCHEMA-2" name="XMLSCHEMA-2">[XML Schema 2]</a>
  </dt>
  <dd>
    <a href="http://www.w3.org/TR/xmlschema-2/">
      <cite>XML Schema Part 2: Datatypes</cite></a>,
      Paul V. Biron, Ashok Malhotra, Editors.
      W3C Recommendation, 2 May 2001, <br />
      http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/.<br />
      <a href="http://www.w3.org/TR/xmlschema-2/">Latest version</a> available at 
      http://www.w3.org/TR/xmlschema-2/.
  </dd>

</dl>
<br />


<h2>
  <a id="SampleOntology" name="SampleOntology">
  Sample Ontologies and Applications
  </a>
</h2>

<dl>
  <dt>
    <a id="IntegratingApplications"
    name="IntegratingApplications">[Integrating Applications]</a>
  </dt>
  <dd>
    <a href="http://www.w3.org/2002/07/swint">
      <cite> Integrating Applications on the Semantic Web</cite>
    </a>, James Hendler, Tim Berners-Lee, and Eric Miller.
    <em>Journal of the Institute of
    Electrical Engineers of Japan</em>, Vol 122(10), October, 2002, p. 676-680.
  </dd>

  <dt><a id="VerticalNet" name="VerticalNet">[VerticalNet]</a></dt>
  <dd>
    <a href="http://www.ksl.stanford.edu/people/dlm/papers/ontologyBuilderVerticalNet-abstract.html">
      <cite>Industrial Strength Ontology Management</cite>
    </a>,
    Aseem Das, Wei Wu, and
    Deborah L. McGuinness. Stanford Knowledge Systems Laboratory Technical
    Report KSL-01-09 2001. In the <em>Proceedings of the International
    Semantic Web Working Symposium</em>, Stanford, CA, July 2001.
  </dd>

  <dt><a id="wine1" name="wine1">[Wine Ontology From Daml.org]</a></dt>
  <dd>
    <a href="http://www.daml.org/ontologies/76">http://www.daml.org/ontologies/76</a>
  </dd>

  <dt><a id="wine4" name="wine4">[Wine Ontology / CLASSIC Tutorial]</a></dt>
  <dd>
    <a href="http://www.bell-labs.com/project/classic/papers/ClassTut/ClassTut.html">
      <cite>Classic Knowledge Representation System Tutorial</cite>
    </a>,
    Deborah L. McGuinness, Peter F. Patel-Schneider, Richmond
    H. Thomason, Merryll K. Abrahams, Lori Alperin Resnick, 
    Violetta Cavalli-Sforza, and Cristina Conati.
    AT&amp;T Bell Laboratories and University of Pittsburgh, 1994.
  </dd>

  <dt><a id="wine2" name="wine2">[Wine Ontology Tutorial]</a></dt>
  <dd>
    <a href="http://www.ksl.stanford.edu/people/dlm/papers/ontology-tutorial-noy-mcguinness-abstract.html">
      <cite>Ontology Development 101: A Guide to Creating Your First Ontology</cite>,
    </a>
    Natalya Fridman Noy and Deborah L. McGuinness.
    Stanford Knowledge Systems Laboratory Technical
    Report KSL-01-05 and Stanford Medical Informatics Technical Report
    SMI-2001-0880, March 2001.
  </dd>

  <dt><a id="wine3" name="wine3">[Wine Ontology in CLASSIC]</a></dt>
  <dd>
    <a href="http://www.ksl.stanford.edu/people/dlm/papers/living-with-classic-abstract.html">
      <cite> Living with CLASSIC: When and How to Use a KL-ONE-Like Language</cite>
    </a>, Ronald J. Brachman, Deborah L. McGuinness , Peter
    F. Patel-Schneider , Lori Alperin Resnick , and Alex
    Borgida. In 
    <em>Principles of Semantic Networks: Explorations in the
    representation of knowledge</em>, John Sowa, Editor.
    Morgan-Kaufmann, San Mateo, California, 1991, pages 401--456.
  </dd>

</dl>

<br />

<h2><a name="RelatedKR">Related KR Language Research</a></h2>

<dl>
  <dt><a id="DAMLPlusOIL" name="DAMLPlusOIL">[DAML+OIL]</a></dt>
  <dd>
    <a id="DAMLPlusOIL-submission" name="DAMLPlusOIL-submission" />
    <a href="http://www.w3.org/Submission/2001/12/">DAML+OIL W3C
    Submission</a>, Includes reference description, both model theoretic
    and axiomatic semantics, annotated walkthrough and examples.
  </dd>
  <dd> 
    <a id="DAMLPlusOIL-walkthrough" name="DAMLPlusOIL-walkthrough" />
    <a href="http://www.w3.org/TR/daml+oil-walkthru/">
      <cite>Annotated DAML+OIL Ontology Markup</cite>
    </a>,
    Dan Connolly, Frank van Harmelen, Ian Horrocks, Deborah McGuinness,
    Peter F. Patel-Schneider, Lynn Andrea Stein. December 2001.  
  </dd>

  <dt>
    <a id="DAML-ONT" name="DAML-ONT">[DAML-ONT]</a>
  </dt>
  <dd>
    <a href="http://www.daml.org/2000/10/daml-ont.html">DAML-ONT initial release</a>
    at http://www.daml.org/2000/10/daml-ont.html.
  </dd>

  <dt><a id="DAML-ONT-KIF" name="DAML-ONT-KIF">[DAML-ONT KIF]</a></dt>
  <dd>
    <a href="http://www.daml.org/2000/10/DAML-Ont-kif-axioms-001107.html">
    Partial DAML-ONT axiomatization
    </a>
    at http://www.daml.org/2000/10/DAML-Ont-kif-axioms-001107.html.<br />
    Defined in <a href="http://logic.stanford.edu/kif/kif.html">KIF</a>
    (http://logic.stanford.edu/kif/kif.html).
  </dd>

  
  <dt>
    <a id="DescriptionLogics" name="DescriptionLogics">[Description
    Logics]</a>
  </dt>
  <dd>
    <a id="dl1" name="dl1"></a>
    <a href="http://titles.cambridge.org/catalogue.asp?isbn=0521781760">
      <cite>
      The Description Logic Handbook: Theory, Implementation and
      Application
      </cite>,
    </a>
    Franz Baader, Diego Calvanese, Deborah
    L. McGuinness, Daniele Nardi, and Peter F. Patel-Schneider, Editors.
    Cambridge University Press, 2002.
  </dd>

  <dt><a id="MCF" name="MCF">[MCF]</a></dt>

  <dd>
    <a href="http://www.w3.org/TR/NOTE-MCF-XML/">
    Meta Content Framework Using XML
    </a>,
    R.V. Guha and Tim Bray. Netscape Communications, 6 June 1997.
  </dd>

  <dt><a id="PartWhole" name="PartWhole">[Part Whole]</a></dt>
  <dd>
  A Taxonomy of Part-Whole
  Relations. M. Winston, R. Chaffin &amp; D. Herrmann. 
    <em>Cognitive Science</em>,
    11:417-444, 1987.
  </dd>

  <dt><a id="XOL" name="XOL">[XOL]</a></dt>
  <dd> 
    <a href="http://www.ai.sri.com/pubs/full.php?id=676">XOL: An XML-Based
    Ontology Exchange Language</a>,
    Peter D. Karp, Vinay K. Chaudhri, and Jerome F. Thomere.
    Technical Report 559. AI Center, SRI 
    International, 333 Ravenswood Ave., Menlo Park, CA 94025, Jul 1999. 
  </dd>

</dl>

<h2><a id="General" name="General">Background Information and Home Pages</a></h2>

<dl> 
  <dt><a id="DublinCore" name="DublinCore">[Dublin Core]</a></dt>
  <dd>
    <a href="http://dublincore.org/">Dublin Core
    Metadata</a> at home page, http://dublincore.org/.
  </dd>

  <dt><a id="DublinCoreXML" name="DublinCoreXML">[Dublin Core XML]</a></dt>
  <dd>
    <a href="http://dublincore.org/documents/2001/11/28/dcmes-xml/">
      <cite>Expressing Dublin Core in RDF/XML</cite>,
    </a>
    Dave Beckett, Eric Brickley, and Dan Brickley.<br />
    Dublin Core Metadata Initiative. July 31, 2002, <br />
    http://dublincore.org/documents/2001/11/28/dcmes-xml/.
  </dd>

  <dt><a id="KAON" name="KAON">[KAON]</a></dt>
  <dd>
    <a href="http://kaon.semanticweb.org/">
    The Karlsruhe Ontology and Semantic Web Tool Suite
    </a>
    at http://kaon.semanticweb.org.
  </dd>

  <dt><a id="OIL" name="OIL">[OIL]</a></dt>
  <dd>
    <a href="http://oil.semanticweb.org/">OIL Home Page</a> at http://oil.semanticweb.org/.
  </dd>

  <dt><a id="Ontobroker" name="Ontobroker">[Ontobroker]</a></dt>
  <dd><a href="http://ontobroker.aifb.uni-karlsruhe.de/index_ob.html">The
  Ontobroker home page</a> at http://ontobroker.aifb.uni-karlsruhe.de/index_ob.html.<br />
  Institute AIFB, University of Karlsruhe.
  </dd>

  <dt><a id="Ontoknowledge" name="Ontoknowledge">[Ontoknowledge]</a></dt>
  <dd>
    <a href="http://www.ontoknowledge.org/">
    Ontoknowledge Home Page
    </a> at http://www.ontoknowledge.org/.
  </dd>

 <dt><a id="RDFHome" name="RDFHome">[RDF Home]</a></dt>
 <dd>
    <a href="http://www.w3.org/RDF/">RDF: Resource Description Framework</a>. 
    Background information at http://www.w3.org/RDF/. 
  </dd>
 
  <dt><a id="SHOE" name="SHOE">[SHOE]</a></dt>
  <dd>
    <a href="http://www.cs.umd.edu/projects/plus/SHOE/">
    Simple HTML Ontology Extensions (SHOE) home page
    </a>
    at http://www.cs.umd.edu/projects/plus/SHOE/.
    University of Maryland.
  </dd>

  <dt><a id="KR" name="KR">[KR]</a></dt>
  <dd>
    <a href="http://kr.org/">KR Home Page</a> at http://kr.org/.
  </dd>

</dl>

<br />  
<hr />
  
<h1><a id="AppendixA" name="AppendixA">Appendix A</a>: XML + RDF Basics</h1>
  
<div class="description">
    This appendix provides links to introductions to the standards that
    OWL depends on.</div>
  
<p>
    To fully understand the OWL syntax and semantics you should be
    familiar with the basics of the  related W3C and IETF standards listed
    below. A minimal guide to XML and RDF is provided by the first two
    links below.
</p>
  
<ul>
  <li><a href="http://www.daml.org/2001/03/daml+oil-walkthru.html#xml-guide"> 
        Appendix</a> to the <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DAMLPlusOIL-walkthrough">
      <em>DAML+OIL Walkthru</em></a><br /><br /></li>
  
  <li><a href="http://www.ietf.org/rfc/rfc2396.txt">URI - Uniform Resource Identifier</a> </li>
  <li><a href="http://www.w3.org/XML/">XML - eXtensible Markup Language</a></li>
  <li><a href="http://www.w3.org/TR/REC-xml-names/">XML Namespaces</a> </li>
  <li><a href="http://www.w3.org/XML/Schema">XML Schema</a></li>
  <li><a href="http://www.w3.org/TR/REC-rdf-syntax/">RDF - Resource Description Framework</a> </li>
  <li><a href="http://www.w3.org/TR/rdf-schema/">RDF Schema</a> </li>
</ul>

<hr />

<h1><a id="AppendixB" name="AppendixB">Appendix B</a>: History</h1>

<p>
<a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#RDF1">The Resource Description Framework (RDF)</a> was the
first language specified by the W3C for representing semantic
information about arbitrary resources.  <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#RDFS">RDF Schema
(RDFS)</a> is a W3C candidate recommendation for an extension to RDF
to describe RDF vocabularies.  RDFS can be used to create ontologies,
but it is purposefully lightweight, with less expressive power than
OWL.  
</p>

<p>
Like OWL, RDFS includes classes and properties, as well as range and
domain constraints on properties.  It provides inheritance hierarchies
for both classes and properties.  Upon its release users began
requesting additional features, including data types, enumerations and
the ability to define properties more rigorously.
</p>

<p>
Other efforts in the research community were already examining exactly
these sorts of features.  For those who wish to delve more deeply into
this background, a partial list of projects and languages includes:
</p>

<ul>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DAMLPlusOIL">DAML - DARPA Agent Markup Language</a></li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DAML-ONT">DAML-ONT</a>  </li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#MCF">MCF - Meta Content Framework</a>.</li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Ontobroker">Ontobroker</a></li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#Ontoknowledge">On-To-Knowledge</a></li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#OIL">OIL - Ontology Inference Layer</a></li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#SHOE">SHOE - Simple HTML Ontology Extensions</a></li>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#XOL">XOL</a></li>
</ul>

<p>
Instead of continuing with separate ontology languages for the
Semantic Web, a group of researchers, including many of the main
participants in both the OIL and DAML-ONT efforts, got together in the
<a href="http://www.daml.org/committee/">Joint US/EU ad hoc Agent
Markup Language Committee</a> to create a new Web ontology language.
This language <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DAMLPlusOIL">DAML+OIL</a> built on both OIL and
DAML-ONT, was <a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#DAMLPlusOIL-submission">submitted</a> to the
W3C as a proposed basis for OWL, and was subsequently selected as the
starting point for OWL.
</p>

<p>
In addition to ontology languages, various taxonomies and existing
ontologies are already in use commercially. In
e-Commerce sites they facilitate machine-based
communication between buyer and seller, enable vertical integration of
markets and allow descriptions to be reused in different marketplaces.
Examples of sites that are actually making commercial use ontologies
include:
</p>

<ul>
<li><a href="http://www.w3.org/TR/2004/REC-owl-guide-20040210/#VerticalNet">VerticalNet</a>
     Vertical Net currently hosts 59 industry-specific e-marketplaces
     that span diverse industries such as manufacturing,
     communications, energy, and healthcare.</li>
</ul>

<p>
Various medical or drug-related ontologies have been developed to help
manage the overwhelming mass of current medical and biochemical research data
that can be difficult to tie together into a cohesive whole.
One major resource is the <a href="http://www.geneontology.org/">Gene
Ontology Consortium</a> which is defining ontologies for
</p>

<ul>
<li>Molecular Function,</li>
<li>Biological Process, and</li>
<li>Cellular Components.</li>
</ul>

<p>
That site also has pointers to ontologies for
</p>

<ul>
<li> sequence attributes, </li>
<li> gene product attributes, </li>
<li> chemical substances,</li>
<li> pathways, </li>
<li> anatomies, </li>
<li> pathology, </li>
<li> physical characteristics, </li>
<li> experiment attributes, </li>
<li> classification, and </li>
<li> pathology. </li>
</ul>

<p> There exist large taxonomies in use today that would be ripe for
extension into the OWL space.  For example, the North American
Industry Classification System (NAICS) defines a hierarchy of over
1900 items that identify industry types.  
NAICS is also tied to the International Standard Industrial
Classification System (ISIC, Revision 3), developed and maintained by
the United Nations. 
</p>

<hr />

<h1>
<a id="changes-since-PR" name="changes-since-PR">
Appendix C: Change Log Since Proposed Recommendation, 15 December 2003
</a>
</h1>

<ul>
 <li>Corrected a typo (allValuesFrom to someValuesFrom) in the TexasThings example in 4.1.</li>
 <li>Added anchor for owl:AnnotationProperty.</li>
 <li>In 3.1.1. added explicit ontology prefix for 'about' syntax example.</li>
 <li>Added a cross reference to the description of the use of <tt>owl:oneOf</tt> in the
     <i>Reference</i> at the end of 5.2.</li>
 <li>Made a number of minor corrections suggested by
     a <a href="http://lists.w3.org/Archives/Public/public-webont-comments/2004Jan/0011.html">
     message</a> to public-webont-comments.
  </li>
 <li>Modified citations for consistency with other OWL documents.</li>
 <li>Fixed typos related to numbering in namespace references.</li>
</ul>

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