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<h1 class="title">
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<img src="/2008/site/images/theme-web-semantics" alt="" />Inference</h1>
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<ul class="w3c_toc">
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<li class="toc_prefix">On this page → </li>
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<li><a href="#summary">what is inference</a>
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<span class="bullet">• </span>
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</li>
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<li><a href="#uses">what  inferece is used for</a>
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<h2 id="summary">What is Inference?</h2>
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<p>Broadly speaking, inference on the Semantic Web can be characterized by
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discovering new relationships. On the Semantic Web, data is modeled as a
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set of (named) relationships between resources. “Inference” means that
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automatic procedures can generate new relationships based on the data
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and based on some additional information in the form of a vocabulary, e.g., a
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set of rules. Whether the new relationships are explicitly added to the
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set of data, or are returned at query time, is an implementation
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issue.</p>
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<p>On the Semantic Web, the source of such extra information can be defined
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via <a href="ontology">vocabularies</a> or rule sets. Both of these approaches draw
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upon knowledge representation techniques. In
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general, ontologies concentrate on classification methods, putting an
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emphasis on defining 'classes', 'subclasses', on how individual
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resources can be associated to such classes, and characterizing the
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relationships among classes and their instances. Rules, on the other
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hand, concentrate on defining a general mechanism on discovering and
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generating new relationships based on existing ones, much like logic
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programs, like Prolog, do. In the family of Semantic Web related W3C
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Recommendations RDFS, OWL, or SKOS are the tools of choice to define ontologies, whereas
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RIF has been developed to cover rule based approaches.</p>
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<h2 id="uses">What Inference is Used For?</h2>
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<p>Inference on the Semantic Web is one of the tools of choice to
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improve the quality of data integration on the Web, by discovering
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new relationships, automatically analysing the content
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of the data, or managing knowledge on the Web in general. Inference
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based techniques are also important in discovering
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possible inconsistencies in the (integrated) data.</p>
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<h2 id="examples">Examples</h2>
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<p>A simple example may help. The data set to be considered may include the
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relationship <tt>(Flipper isA Dolphin)</tt>. An ontology may declare that “every
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Dolphin is also a Mammal”. That means that a Semantic Web program
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understanding the notion of “X is also Y” can add
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the statement <tt>(Flipper isA Mammal)</tt> to the set of
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relationships, although that was not part of the original data. One can also say that the new relationship
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was “discovered”. Another example is to express that fact that “if two
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persons have the same name, home page, and email address, then they are
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identical”. In this case, the “identity” of two resources can be
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discovered via inferencing.</p>
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<p>Usage and techniques of ontologies and rules largely overlap. Very
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broadly speaking, ontologies optimize for taxonomic reasoning problems,
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and rule based systems optimize for reasoning problems within the data.
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The difference is largely a matter of style, and criteria like available
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expertise, ease of adapting to existing data, tooling support, maturity
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and costs, etc., should be considered as far more important when trying
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to choose.</p>
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<h2 id="learnmore">Learn More</h2>
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<p>The Semantic Web community maintains a <a href="http://esw.w3.org/topic/SwBooks">list of books</a>
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on a W3C Wiki page. Some of those books
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are introductory in nature while others are conference proceedings or
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textbook that address more advanced topics.
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Details of <a href="http://www.w3.org/2007/11/Talks/Semantic_Web.html">recent and upcoming
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Semantic Web related talks</a>, given by the <a href="http://www.w3.org/People/">W3C Staff</a>,
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the <a href="http://www.w3.org/Consortium/Offices/">staff of the W3C Offices</a>,
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and members of the W3C Working Groups are available separately; the slides
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are usually publicly available. The
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W3C also maintains a <a href="http://www.w3.org/2001/sw/sweo/public/UseCases/">collection of Semantic
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Web Case Studies and Use Cases</a> that
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show how Semantic Web technologies, including inference, is used in
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practice. Finally, the <a href="/2001/sw/SW-FAQ">Semantic Web FAQ</a> may also be of help
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in understanding the various concepts.</p>
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<div id="pressreleases"></div>
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<div id="recentpress"><!-- end generated recent press --></div>
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<h2 id="specifications">Current Status of Specifications</h2>
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<p>Learn more about the current status of specifications related
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to:
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<a href="http://www.w3.org/2005/rules/wg.html">Rule Interchange Format Working Group</a>
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<a href="http://www.w3.org/2007/OWL/">OWL Working Group</a>
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<a href="http://www.w3.org/2001/sw/interest/">Semantic Web Interest Group</a>
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<a href="/standards/techs/rif">RIF Rule Interchange Format</a>
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