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        <title>Semantic Web Frequently Asked Questions</title>
        <link>http://www.w3.org/2001/sw/SW-FAQ</link>
        <description>Semantic Web Frequently Asked Questions</description>
        <dc:source>http://www.w3.org/2001/sw/SW-FAQ</dc:source>
        <dc:date>2009-04-28T00:00+00:00</dc:date>
 
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:rights>Copyright © 2009 World Wide Web Consortium (W3C)</dc:rights>

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    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#swgoals">
        <title>How would you define the main goals of the Semantic Web?</title>
        <dc:subject>How would you define the main goals of the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#swgoals</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				
            <p>The <em>Semantic Web is a Web of data</em>. There is a lot of data we all use every day, and it's not part of the Web. For example, I can see my bank statements on the web, and my photographs, and I can see my appointments in a calendar. But can I see my photos in a calendar to see what I was doing when I took them? Can I see bank statement lines in a calendar? Why not? Because we don't have a web of data. Because data is controlled by applications, and each application keeps it to itself.
				</p>
			
			  
            <p>
				The vision of the Semantic Web is to extend principles of the Web from documents to data. Data should be accessed using the general Web architecture using, e.g., URI-s; data should be related to one another just as documents (or portions of documents) are already. This also means creation of a common framework that allows data to be shared and reused across application, enterprise, and community boundaries, to be processed automatically by tools as well as manually, including revealing possible new relationships among pieces of data. 
			  </p>
			  	
			  
            <p>
				Semantic Web technologies can be used in a variety of application areas; for example:
				in <em>data integration</em>, whereby data in various locations and various formats can
				be integrated in one, seamless application; in <em>resource discovery and
				classification</em> to provide better, domain specific search engine capabilities; in
				<em>cataloging</em> for describing the content and content relationships available at a
				particular Web site, page, or digital library; by <em>intelligent software agents</em>
				to facilitate knowledge sharing and exchange; in <em>content rating</em>; in describing
				<em>collections</em> of pages that represent a single logical “document”; for
				describing <em>intellectual property rights</em> of Web pages (see, eg, the <a href="http://creativecommons.org/technology/usingmarkup" shape="rect">Creative Commons</a>), and in many
				others.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#othersw">
        <title>Are there any other definitions or thought of Semantic Web, if any?</title>
        <dc:subject>Are there any other definitions or thought of Semantic Web, if any?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#othersw</link>
        <dc:date>2008-06-27T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				No <em>formal</em> definitions, but of course there are different approaches. Indeed, the complexity and variety of applications referring to the Semantic Web is increasing every day, which means that various application areas, implementers, developers, etc, would emphasize different aspects of Semantic Web technologies. This wide range of applications include data integration, knowledge representation and analysis, cataloguing services, improving search algorithms and methods, social networks, etc. 
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whatarebuildingblocks">
        <title>What are the major building blocks of the Semantic Web?</title>
        <dc:subject>What are the major building blocks of the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whatarebuildingblocks</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				In order to achieve the goals <a href="#swgoals" shape="rect">described above</a>, the most
				important is to be able to define and describe the relations among data (i.e.,
				resources) on the Web. This is not unlike the usage of hyperlinks on the current Web
				that connect the current page with another one: the hyperlinks defines a relationship
				between the current page and the target. One major difference is that, on the Semantic
				Web, such relationships can be established between <em>any</em> two resources, there is
				no notion of “current” page. Another major difference is that the relationship
				(i.e, the link) itself is <em>named</em>, whereas the link used by a human on the
				(traditional) Web is not and their role is deduced by the human reader. The definition
				of those relations allow for a better and automatic interchange of data. <a href="#whrdf" shape="rect">RDF</a>, which is one of the fundamental building blocks of the Semantic Web,
				gives a formal definition for that interchange.
			  </p>
			  
            <p>
				On that basis, additional building blocks are built around this central notion. Some
				examples are:
			  </p>
			  
            <ul>
				
               <li>Tools to query information described through such relationships (eg, SPARQL)
				</li>
				
               <li>Tools to have a finer and more detailed classification and characterization of
				those relationships as well as the resources being characterized. This ensures interoperability,
				more complex automatic behaviors. For example, a community can agree what name to use for a relationship
				connecting a page to one’s calendar; this name can then be used by a large number of
				users and applications without the necessity to redefine such names every time. 
				(E.g., RDF Schemas, OWL, SKOS)
				</li>
				
               <li>For more complex cases, tools are available to define logical relationships among
				resources and their relationships (for example, if a relationships binds a person to
				his/her email address, it is feasible to declare that the email address is unique, ie,
				the address is not shared by several persons). Tools based on this level (e.g., OWL, Rules) can ensure
				more interoperability, can reveal inconsistencies and find new relationships. 
				</li>
				
               <li>Tools to extract from, and to bind to traditional data sources to ensure their
				interchange with data from other sources. (E.g., GRDDL, RDFa)
				</li>
			  
            </ul>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whatarekillerapps">
        <title>What is the “killer application” for the Semantic Web?</title>
        <dc:subject>What is the “killer application” for the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whatarekillerapps</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				It is difficult to predict what a “killer application” is for a specific
				technology, and the prediction is often erroneous. That said, the integration of
				currently unbound and independent “silos” of data in a coherent application is
				certainly a good candidate. Specific examples are currently explored in areas like
				<a href="http://esw.w3.org/topic/SemanticWebForLifeSciences" shape="rect">Health Care and Life
				Sciences</a>, <a href="http://www.swed.org.uk" shape="rect">Public Administration</a>, <a href="http://www.swop-project.eu/" shape="rect">Engineering</a>, etc.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#swonbrowser">
        <title>Will I “see” the Semantic Web in my everyday browser?</title>
        <dc:subject>Will I “see” the Semantic Web in my everyday browser?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#swonbrowser</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Not necessarily, at least not directly. The Semantic Web technologies may act behind
				the scenes, resulting in a better user experience, rather than directly influencing the
				“look” on the browser. This is already happening: there are Web Sites (e.g.,
				Sun’s <a href="http://www.sun.com/servers/wp.html/" shape="rect">white paper collection site</a>,
				or Nokia’s <a href="http://www.forum.nokia.com/" shape="rect">support portal for their S60 series
				device</a>, <a href="http://pressroom.oracle.com/" shape="rect">Oracle’s virtual press room</a>,
				<a href="http://www.harpers.org/" shape="rect">Harper’s online magazine</a>, or 
				<a href="http://finance.yahoo.com" shape="rect">Yahoo!’s Finance portal</a>) that use Semantic Web
				technologies in the background.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#isthisresearch">
        <title>Is the Semantic Web just research, or does it have industrial applications?</title>
        <dc:subject>Is the Semantic Web just research, or does it have industrial applications?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#isthisresearch</link>
        <dc:date>2007-07-29T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				As all innovative technologies, the Semantic Web underwent an evolution starting at
				research labs, being then picked up by the Open Source community, then by small and
				specialized startups and finally by business in general. Remember: the Web was
				originally developed in a High Energy Physics center!
			  </p>
			  
            <p>
				At present, the Semantic Web is increasingly used by small and large business. <a href="http://www.oracle.com/technology/tech/semantic_technologies/index.html" shape="rect">Oracle</a>,
				<a href="http://www.alphaworks.ibm.com/tech/semanticstk" shape="rect">IBM</a>, <a href="http://www.adobe.com/products/xmp/index.html" shape="rect">Adobe</a>, <a href="http://www.softwareag.com/corporate/news/pressroom/pressreleases/20050309_enterprise_information_integration_page.asp" shape="rect">
				Software AG</a>, or <a href="http://www.yahoo.com" shape="rect">Yahoo!</a> are only some of the large corporations that have picked up this technology
				already and are selling tools as well as complete business solutions. Large application
				areas, like the <a href="http://esw.w3.org/topic/SemanticWebForLifeSciences" shape="rect">Health
				Care and Life Sciences</a>, look at the data integration possibilities of the Semantic
				Web as one of the technologies that might offer significant help in solving their
				R&amp;D problems.
			  </p>
			  
            <p>It is worth consulting the list of <a href="http://www.w3.org/2001/sw/sweo/public/UseCases/" shape="rect">Semantic Web Case Studies and Use Cases</a>; it gives a good overview of existing applications. Note that the list is often updated, when new application examples come in.</p>		  
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#complication">
        <title>Does one have to understand the theory of formal ontologies and logic to use the Semantic Web?</title>
        <dc:subject>Does one have to understand the theory of formal ontologies and logic to use the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#complication</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				First of all, <a href="#whmustont" shape="rect">as pointed out elsewhere in this document</a>, one
				can develop Semantic Web applications without using ontologies. Very useful
				applications can be built without those, relying on the most fundamental, and simple
				concept of the Semantic Web. However, even if ontologies, rules, reasoners, etc, are
				used, the average user should not care about the complexities of, say, the details of
				reasoning. All this is done “under the hood”. What the developer needs to operate
				with are usually simple logical patterns of the sort “Given that
				<code>(Flipper isA Dolphin)</code> and <code>(Dolphin isAlso Mammal)</code>, one
				can conclude that <code>(Flipper isA Mammal)</code>".
			  </p>
			  
            <p>
				Compare it to SQL. The official SQL standards, the formal semantics of SQL, and indeed
				its implementations, are extremely complex and understood by a few specialists only.
				Nevertheless, a large number of users use SQL in practice, without caring about the
				underlying complexities.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relateweb">
        <title>How is the Semantic Web related to the existing Web?</title>
        <dc:subject>How is the Semantic Web related to the existing Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relateweb</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The Semantic Web is an <em>extension</em> of the current Web and not its replacement.
				Islands of RDF and possibly related ontologies can be developed incrementally. Major
				application areas (like Health Care and Life Sciences) may choose to “locally”
				adopt Semantic Web technologies, and this can then spread over the Web in general. In
				other words, one should not think in terms of “rebuilding” the Web.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#datacopyright">
        <title>Aren't there major copyright questions if the data in an integration process are cached?</title>
        <dc:subject>Aren't there major copyright questions if the data in an integration process are cached?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#datacopyright</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  There are and there aren't. There is just the way the Web raises this issue already;
			  after all, documents browsed by a traditional browser are usually cached on the client
			  side. And there aren't, because this does not seem to have created major problems on the
			  Web so far, and the Semantic Web is not fundamentally different in this respect.
			</div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#swactivity">
        <title>What is the Semantic Web activity at W3C?</title>
        <dc:subject>What is the Semantic Web activity at W3C?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#swactivity</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>WhatIsTheSW</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The <a href="/2001/sw/" shape="rect">Semantic Web Activity</a> at W3C groups together all the
				Working and Interest Groups whose goals are to improve the current Semantic Web
				technologies or to contribute to their wider adoption. The <a href="/2001/sw/" shape="rect">activity
				home page</a> gives an up-to-date list of the current work at W3C.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relAI">
        <title>… Artificial Intelligence?</title>
        <dc:subject>… Artificial Intelligence?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relAI</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Some parts of the Semantic Web technologies are based on results of Artificial
				Intelligence research, like knowledge representation (e.g., for ontologies), model
				theory (e.g., for the precise semantics of RDF and RDF Schemas), or various types of
				logic (e.g., for rules). However, it must be noted that Artificial Intelligence has a
				number of research areas (e.g., image recognition) that are completely orthogonal to
				the Semantic Web.
			  </p>
			  
            <p>
				It is also true that the development of the Semantic Web brought some new perspectives
				to the Artificial Intelligence community: the “Web effect”, i.e., the merge of
				knowledge coming from different sources, usage of URIs, the necessity to reason with
				incomplete data; etc.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relDL">
        <title>… Description Logic?</title>
        <dc:subject>… Description Logic?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relDL</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Description Logic is the mathematical theory (stemming from knowledge representation)
				that is at the basis of some of the technologies defined on the Semantic Web: OWL-DL
				and OWL-Lite.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relXML">
        <title>… XML? When should I use RDF and when should I use XML?</title>
        <dc:subject>… XML? When should I use RDF and when should I use XML?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relXML</link>
        <dc:date>2008-01-31T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Both formalisms have their strengths and weaknesses; their area of usage is different.
				The two data models serve different constituencies and the choice really depends on the
				application. There is no better or worse; only different.
			  </p>
			  
            <p>
				One of XML’s strengths is its ability to describe strict hierarchies. Applications
				may rely on and indeed exploit the position of an element in a hierarchy: for example,
				most browsers provide a different rendering of HTML’s <code>li</code> element
				depending on how “deep” the enclosing list is. XML makes it easy to control the
				content via XML Schemas and combine XML data that abide to the same Schema or DTD.
			  </p>
			  
            <p>
				However, combining <em>different</em> XML hierarchies (technically, DOM trees) within
				the same application may become very complex. XML is not an easy tool for <em>data
				integration</em>. On the other hand, RDF consists of a very loose set of relations
				(triples). Due to its <a href="#weburi" shape="rect">usage of URIs</a> it is very easy to seamlessly
				merge triple sets, ie, data described in RDF within the same application; it is
				therefore ideal for the integration of possibly heterogenous information on the Web.
				But this has its price: reconstructing hierarchies from RDF may become quite complex.
				As an example, it would be fairly complicated (and unnecessary) to describe, eg, vector
				graphics, using RDF; use <a href="http://www.w3.org/Graphics/SVG/" shape="rect">SVG</a> instead!
			  </p>
			  
            <p>For existing XML-based vocabularies, one can develop an
				<a href="http://www.w3.org/TR/grddl-primer/" shape="rect">GRDDL transformation</a> to RDF
				using a language such as XSLT and then use the power of RDF to merge
				your pre-existing XML formats. For new vocabularies, this technique	
				allows you to use both XML and RDF-based versions of your vocabulary,
				gaining the advantages of both.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relXMLS">
        <title>… XML Schemas? What do ontologies buy me that XML and XML Schema don't?</title>
        <dc:subject>… XML Schemas? What do ontologies buy me that XML and XML Schema don't?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relXMLS</link>
        <dc:date>2008-01-31T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				This issue is also related to the issue of using XML or RDF, addressed in a <a href="#relXML" shape="rect">previous question</a>. First of all, let us quote from the <a href="/TR/owl-guide/" shape="rect">OWL Guide recommendation</a>:
			  </p>
			  
            <blockquote>
				
               <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 <code>PurchaseOrder</code>
				  message, transfer <code>Amount</code> dollars from <code>AccountFrom</code> to <code>
					AccountTo</code> and ship <code>Product</code>.” 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
					<code>Product</code> is a type of <code>Chardonnay</code> it must also be a white
					wine.
				  </li>
				  
                  <li>One advantage of OWL ontologies will be the availability of tools that can reason
				  about them. Tools will provide generic 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. […] 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.
				  </li>
				
               </ul>
			  
            </blockquote>
			  
            <p>
				Also, XML data is very sensitive to the XML Schema it refers to. If the XML Schema
				changes, the <em>same</em> XML data may become invalid, i.e., being rejected by
				Schema-aware parsers. Somewhat similar dependence on RDF Schemas and Ontologies exist
				for RDF data, too: if the RDF Schema or OWL Ontology changes, the inferences drawn from
				the RDF data may change. However, the core RDF data is still usable, there is no notion
				of the data being “rejected” by, e.g., a parser due to a Schema/Ontology change. In
				general, RDF is more robust against changing of Schemas and Ontologies than XML is
				versus Schemas. Note that a GRDDL transformation from XML to RDF may be given by an XML Schema as
				<a href="http://www.w3.org/TR/grddl/#ns-bind" shape="rect">described in the GRDDL
				specification</a>. This allows any XML document that validates according
				to the XML Schema given at the namespace URI of the XML vocabulary to be
				converted to RDF.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relHTMLMeta">
        <title>… HTML meta headers?</title>
        <dc:subject>… HTML meta headers?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relHTMLMeta</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The <code>meta</code> and <code>link</code> elements in HTML can be used to add
				metadata to an HTML page. In Semantic Web terms, this is equivalent to the process of
				defining RDF relationships for that page as a “source”. Note, however, that these
				elements can be used to define relationships for the enclosing HTML file only, whereas
				the Semantic Web allows the definition of relationships on <em>any</em> resource on the
				Web. That also means that the <code>meta</code> and <code>link</code> elements can be
				used <em>by the author of the document only</em>, whereas, on the Semantic Web, anybody
				could publish metadata concerning that page. GRDDL allows easy and automatic extraction of meta header
				data, such as that given by Dublin Core, to RDF.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#reltag">
        <title>… tagging, folksonomies</title>
        <dc:subject>… tagging, folksonomies</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#reltag</link>
        <dc:date>2007-11-27T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Tagging has emerged as a popular method of categorizing content. Users are allowed to
				attach arbitrary strings to their data items (for example, blog entries and
				photographs). 
				While tagging is easy and useful, it often discards a lot of
				the semantics of the data. A folksonomy tag is typically 2/3 of an RDF
				triple. The subject is known: e.g., the URL for the flickr image being
				tagged, or the URL being bookmarked in delicious. The object is known:
				e.g.,  <code>http://flickr.com/photos/tags/cats</code> or
				<code>http://del.icio.us/tag/cats</code>. But the predicate to connect them is
				often missing. <a href="http://www.flickr.com/groups/api/discuss/72157594497877875/" shape="rect">Machine-tags</a>
				lend themselves to RDF more since they better capture the relationship between the subject 
				and the object. Folksonomy providers are encouraged to capture or infer the semantics
				around their tags and to leverage semantic web technologies such as
				RDF and SKOS to publish machine readable versions of their concept
				schemes.
			  </p>
			  
            <p>Another issue arising with tags is that the number of different tags meaning the same things but differing in spelling, lower or upper case, usage of space or underscore characters etc., may create major obstacles to them being used on a larger scale. There are a number of initiatives, start-up companies, projects, etc., that aim at combining the two approaches, providing a little bit of extra rigour using Semantic Web techniques to create new type of applications (<a shape="rect" hreflang="http://www.opencalais.com/">Reuters’ Open Calais service</a>, <a shape="rect" hreflang="http://www.twine.com">Radar Networks’ Twine</a>, the <a href="http://moat-project.org/" shape="rect">MOAT initiative</a>, <a href="http://tagcommons.org/" shape="rect">Tag Commons</a>, etc.).</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relmf">
        <title>… microformats</title>
        <dc:subject>… microformats</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relmf</link>
        <dc:date>2008-01-31T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Microformats are usually relatively small and simple sets of terms agreed upon by a
				community. Data models developed within the framework of the Semantic Web have the
				potential to be more expressive, rigorous, and formal (and are usually larger). Both
				can be used to express structured data within web pages. In some cases, microformats
				are appropriate because the extra features provided by Semantic Web technologies are
				not necessary. Other cases requiring more rigor will not be able to use microformats.
			  </p>
			  
            <p>
				Data described in microformats each address a <em>specific</em> problem area. One has
				to develop a program well-adapted to a particular microformat, to the way it uses, say,
				the class and property="dc:date" content attributes. It also becomes difficult (though possible) to combine
				different microformats. In contrast, RDF can represent <em>any</em>
				information—including that extracted from microformats present on the page. This is
				where microformats can benefit from RDF—the generality of the Semantic Web tools
				makes it easier to reuse existing tools, eg, a query language and combining statements
				from different origins easily belongs to the very essence of the Semantic Web.
			  </p>
			  
            <p>
				
               <a href="http://www.w3.org/2001/sw/grddl-wg/" shape="rect">GRDDL</a> is a “bridge” to the
				microformats approach; it defines a general procedure whereby
				microformats stored in an XHTML file can be transformed into RDF
				on–the–fly. A list of microformat to RDF vocabulary can be found on
				<a href="http://esw.w3.org/topic/CustomRdfDialects" shape="rect">on the ESW Wiki</a>. 
				Another technology is <a href="http://www.w3.org/TR/rdfa-syntax" shape="rect">RDFa</a> that defines an XHTML1.1 module that gives the possibility to use virtually any RDF vocabulary as annotations of the XHTML
				content; a bit like microformats with somewhat more rigor and a better way of
				<em>integrating</em> different vocabularies within the same document. Finally, <a href="http://research.talis.com/2005/erdf/wiki/Main/RdfInHtml" shape="rect">eRDF</a> (developed by Talis)
				offers a formalism somewhere between the two: one can add general RDF data to an
				(X)HTML page without the need for a new module, although with restrictions on the type
				of RDF vocabularies that can be used.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#relweb2">
        <title>… Web 2.0?</title>
        <dc:subject>… Web 2.0?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#relweb2</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoesTheSWRelatesTo</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				One aspect of Web 2.0, beyond the exciting new interfaces and the usage of a common intelligence, is that it pushes
				intelligence and active agents from the server to the client, more specifically the
				browser. Development of active client-side application also means that these
				applications use all kinds of <strong>data</strong>; data that are on the Web
				somewhere, or data that is embedded in the page though not necessarily visible on the
				screen. Examples are microformats type annotation of the page, calendar data on the
				Web, tagged images or links stored on a web site, etc. This aspect of Web 2.0, ie, that
				applications are based on <em>combining</em> various types of data (“mashing up”
				the data) that are spread all around on the Web coincides with the very essence of the
				Semantic Web. What the Semantic Web provides is a more consistent model and tools for
				the definition and the usage of qualified relationships among data on the Web. I.e.,
				both technologies focus on intelligent data sharing. A number of typical Web 2.0
				demonstrations and applications emerge that, in the background, use Semantic Web tools
				combined with AJAX and other, exciting user interface approaches.
			  </p>
			  
            <p>
				In many cases, using RDF-based techniques makes the mashing up process easier, mainly
				when data collected by one application is reused by another one somewhere down the
				line. The general nature of RDF makes this “mashup chaining” straightforward, which
				is not always the case for simpler Web 2.0 applications.
			  </p>
			  
            <p>Trying to present these two approaches as alternatives, or even claiming folksonomies to be superior to the Semantic Web approach, has been a topic of the blogosphere and various publications for a while, but both communities realize these days that these two techniques are complementary rather than competitive. </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#Manual">
        <title>Does the Semantic Web require me to manually markup all the existing web-pages, or to convert all the data in relational databases into RDF?</title>
        <dc:subject>Does the Semantic Web require me to manually markup all the existing web-pages, or to convert all the data in relational databases into RDF?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#Manual</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The Semantic Web is about a web of data. The data itself can reside in databases,
				spreadsheets, Wiki pages, or indeed traditional web pages.
			  </p>
			  
            <p>
				The challenge is to develop tools that can “export” these data into RDF form: RDF
				plays the role of a common model, as a kind of a “glue” to integrate the data. That
				does <em>not</em> mean that the data must be <em>physically converted</em> into RDF
				form and stored in, say, RDF/XML. Instead, automatic procedures, for example <a href="http://esw.w3.org/topic/RdfAndSql" shape="rect">SQL to RDF converters</a> for relational databases,
				<a href="grddl-wg/" shape="rect">GRDDL</a> processors for XHTML files with <a href="http://en.wikipedia.org/wiki/Microformats" shape="rect">microformats</a>, <a href="http://www.w3.org/TR/rdfa-syntax" shape="rect">RDFa</a>, etc, can produce RDF data
				on-the-fly as an answer to, eg, queries. RDF data may also be included in the data via
				other tools (e.g, <a href="http://www.adobe.com/products/xmp/index.html" shape="rect">Adobe’s
				XMP</a> data that gets automatically added to JPEG images by Photoshop). Authoring
				tools also exist to develop, eg, ontologies on a high level instead of editing the
				ontology files directly. Of course, direct editing of RDF data is sometimes necessary,
				but it can be expected to become less and less prevalent as smarter editors come to the
				fore.
			  </p>
			  
            <p>
				Clearly, lots of development is still to be done in this area, and it is a subject of
				active Research and Development. The goal is to reuse, as much as possible,
				<em>existing</em> data in its <em>existing</em> form, and minimize the RDF data that
				has to be created manually.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#publd">
        <title>Does the Semantic Web require me to put all my data into the public domain? What about my sensitive data?</title>
        <dc:subject>Does the Semantic Web require me to put all my data into the public domain? What about my sensitive data?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#publd</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The Semantic Web provides an application framework that <em>extends</em> the current
				Web, does not replace it. That also means that the current infrastructure of firewalls,
				various levels of protections, encryption, etc, remain in place. If, for whatever
				reason (privacy, business, etc), the data should be kept behind the firewall on the
				Intranet, rather than being in the open, this just means that that particular Semantic
				Web application operates on the Intranet. This is not unlike the development of the
				traditional Web, the usage of Web Services, etc: a number of applications were
				developed to be used behind corporate firewalls; some of them migrated later to the
				full Web, some other stayed behind the firewall. The same is valid for Semantic Web
				applications.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#tools">
        <title>Where do I find tools for Semantic Web development?</title>
        <dc:subject>Where do I find tools for Semantic Web development?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#tools</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				There are several lists on the Web that give a more-or-less comprehensive overview of
				the various available tools. There is a <a href="http://esw.w3.org/topic/SemanticWebTools" shape="rect">Wiki page</a> on the W3C ESW Wiki site that
				is maintained by the W3C staff as well as the community at large. This page includes
				references to programming environments, validators that can be used to validate RDF/XML
				data or OWL ontologies, SPARQL endpoints, specialized editors or triple databases. It
				also includes references to other lists, like <a href="http://planetrdf.com/guide/" shape="rect">Dave Beckett's Resource Description Framework (RDF)
				Resource Guide</a> or the tool list <a href="http://www.wiwiss.fu-berlin.de/suhl/bizer/toolkits/index.htm" shape="rect">maintained at the <span>Freie Universität Berlin</span>
               </a>.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#toolqual">
        <title>Are the SW tools as robust and as ubiquitous as, say, the xerces XML parser?</title>
        <dc:subject>Are the SW tools as robust and as ubiquitous as, say, the xerces XML parser?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#toolqual</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				In general most of the tools are of a good quality already. On the open source domain
				<a href="http://jena.sourceforge.net" shape="rect">Jena</a>, <a href="http://sourceforge.net/projects/sesame/" shape="rect">Sesame</a>, or <a href="http://librdf.org/" shape="rect">Redland</a>, for example, can easily be compared to xerces in
				their widespread usage and richness of features; databases like <a href="http://mulgara.org/" shape="rect">Mulgara</a> or <a href="http://virtuoso.openlinksw.com/" shape="rect">Virtuoso</a> are 
				also in widespread use and have undergone a very thorough development in the past few years. There are more and more commercial tools, including editors, professional databases, content management
				systems, ontology creation and validation tools, etc. The <a href="http://esw.w3.org/topic/SemanticWebTools" shape="rect">Wiki page</a> on the W3C ESW Wiki site gives
				a good overview of most of those.
			  </p>
			  
            <p>
				Obviously, there is room for improvement. SW is a younger technology than XML and it
				still needs time to catch up and have tools of the same maturity and efficiency level
				than the XML World. However, huge improvements have already been made in the past few
				years in all areas, and large-scale enterprise deployment is also happening already. In
				general: availability of tools is not a reason any more for not developing Semantic Web
				applications…
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#rdfxhtml">
        <title>How do I put RDF into my (X)HTML Pages?</title>
        <dc:subject>How do I put RDF into my (X)HTML Pages?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#rdfxhtml</link>
        <dc:date>2008-06-27T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Until recently, it was not possible to incorporate full RDF into XHTML without
				violating the validity of the resulting XHTML, except for the usage of the
				<code>meta</code> and the <code>link</code> elements in the header.
				The best solution was to store the RDF separately and use the URIs to refer to the XHTML
				page and the <code>link</code> element in the XHTML page to refer to the RDF content.
				This technique is often called an RDF autodiscovery link and is used by a number of
				tools already.
			  </p>
			  
            <p>However, this has changed with the newer developements of GRDDL and of RDFa. The <a href="http://www.w3.org/TR/grddl-primer/" shape="rect">GRDDL</a> provides a “bridge” to the
				microformats approach while <a href="http://www.w3.org/TR/xhtml-rdfa-primer/" shape="rect">RDFa</a> provides an XHTML1.1 module that gives the possibility to use virtually any RDF vocabulary as annotations
				of the XHTML content, yielding RDF data.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#reldb">
        <title>How do I export my data from a Relational Database?</title>
        <dc:subject>How do I export my data from a Relational Database?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#reldb</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				This is one of the active areas of R&amp;D, and no final answer is yet available. In
				general, methods exist to convert RDF queries (e.g., in SPARQL) into SQL queries
				on-the-fly; ie, the RDB looks like an RDF store when queried by an RDF tool. The
				details of the mapping from Relational Tables to RDF notions is usually described for a
				specific database using either a small ontology and/or a set of rules; this is the only
				manual information to be generated for the conversion. General solutions begin to
				emerge, but work still has to be done (and is part of the future plans of W3C). See the
				<a href="http://esw.w3.org/topic/RdfAndSql" shape="rect">W3C Wiki page</a> for further details.
			  </p>
			  
            <p>Note that W3C has recently formed an <a shape="rect" hreflang="http://www.w3.org/2005/Incubator/rdb2rdf/">RDB2RDF</a> Incubator Group looking at this issue more closely. Results of the group should be available early 2009.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#learn">
        <title>How can I learn more about the Semantic Web?</title>
        <dc:subject>How can I learn more about the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#learn</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				
               <a href="http://planetrdf.com/guide/" shape="rect">Dave Beckett's Resource Description Framework
				(RDF) Resource Guide</a> gives a quite comprehensive list of references to Semantic Web
				related articles. The <a href="/2001/sw/" shape="rect">home page of the Semantic Web Activity</a>
				lists all the recommendations, gives references to some of the presentations, articles,
				etc, that have been given by the W3C staff or the members of the working groups on the
				subject. A <a href="http://www.w3.org/2001/sw/BestPractices/Tutorials" shape="rect">separate page
				lists</a> a number of tutorials that might be of interest.
			  </p>
			  
            <p>
				The (now defunct) <a href="http://www.w3.org/2001/sw/BestPractices" shape="rect">Semantic Web Best
				Practices and Deployment Working Group</a> has produced a number of notes that might be
				useful when developing ontologies, setting up servers to serve RDF data, using XML
				Schema datatypes with RDF, etc. 
			  </p>
			  
            <p>
				A number of books have also been published. A <a href="http://esw.w3.org/topic/SwBooks" shape="rect">list of books is given on W3C’s Wiki site</a>,
				comprising (at this moment) over 40 books in different languages, published by major
				publishers like O’Reilly, MIT Press, Cambridge University Press, Springer
				Verlag, …
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#papers">
        <title>Where can I find papers/publications about the Semantic Web?</title>
        <dc:subject>Where can I find papers/publications about the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#papers</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				There are a number of conference series that are either dedicated to the Semantic Web
				or which always have a significant Semantic Web track. The best known are:
			  </p>
			  
            <ul>
				
               <li>The “International Semantic Web Conference” series is a yearly event that
				publishes its proceedings by Springer (the proceedings are <a href="http://iswc2006.semanticweb.org/" shape="rect">online since 2006</a>). While these conferences
				typically circulate around the globe, the “European Semantic Web Conference” and
				the “Asian Semantic Web Conference” series are held somewhere in Europe,
				respectively in Asia.
				</li>
				
               <li>
				  
                  <a href="http://www.iw3c2.org/" shape="rect">The “International World Wide Web
				  Conference”</a> is a major yearly conference on World Wide Web Technologies in general,
				  which always has a strong Semantic Web track both for the academic and the
				  developers’ communities. Look at the <a href="http://www.iw3c2.org" shape="rect">page of the
				  organizing committee</a> for further details on these conferences and links to their
				  proceedings.
				</li>
				
               <li>The yearly <a href="http://www.semantic-conference.com/" shape="rect">Semantic Technologies</a> conference has also become a major event. It is less focussed on the research aspects of the Semantic Web but concentrates rather on the industrial, business aspects, new applications and developments.</li>
			  
            </ul>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#findont">
        <title>Where do I find ontologies, terminologies, or datasets for my applications?</title>
        <dc:subject>Where do I find ontologies, terminologies, or datasets for my applications?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#findont</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				There are several portals that collect information on existing ontologies. A good
				example is <a href="http://www.schemaweb.info/" shape="rect">SchemaWeb</a>. Another one is the
				<a href="http://pingthesemanticweb.com/" shape="rect">“PingTheSemanticWeb”</a> service which
				collects information about new RDF documents on the Web based on “pings” sent by
				applications generating data and on RDF autodiscovery links found by people browsing
				the Web. It currently contains information about ~7 million RDF files. There are also
				search engines, like <a href="http://swoogle.umbc.edu/" shape="rect">Swoogle</a>, <a href="http://iws.seu.edu.cn/services/falcons/objectsearch/index.jsp" shape="rect">Falcon</a>, <a href="http://www.sindice.com/query/keyword" shape="rect">Sindice</a> and others (see the
				<a href="http://esw.w3.org/topic/SemanticWebTools#head-09ab45ef1fb5d28af30c2787c5ef6705329abc5d" shape="rect">separate section on the tool’s wiki page</a>) that specialize on searching Semantic Web documents.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#semwebdataview">
        <title>Can I see Semantic Web data directly in my browser?</title>
        <dc:subject>Can I see Semantic Web data directly in my browser?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#semwebdataview</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				You can have a human-readable display of RDF data by using RDF data browsers like
				<a href="http://dig.csail.mit.edu/2005/ajar/ajaw/tab.html" shape="rect">the Tabulator</a>, <a href="http://www4.wiwiss.fu-berlin.de/rdf_browser/" shape="rect">Disco</a>, or the <a href="http://demo.openlinksw.com/DAV/JS/rdfbrowser/index.html" shape="rect">OpenLink RDF Browser</a>, and
				web browser extensions like <a href="http://simile.mit.edu/wiki/Piggy_Bank" shape="rect">PiggyBank</a> or the <a href="http://sioc-project.org/firefox" shape="rect">Semantic Radar</a>. While end users will not have a
				need to see Semantic Web data (instead they will benefit from better information
				systems built on top of it) it may be helpful to developers to be aware of Semantic Web
				data directly so that they can use this information in their applications.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#community">
        <title>Is there a community of developers I can join?</title>
        <dc:subject>Is there a community of developers I can join?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#community</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The <a href="http://www.w3.org/2001/sw/interest/" shape="rect">W3C Semantic Web Interest Group</a>
				is one of those and probably the best place to join first. It is a public mailing list
				and is also active on the #swig IRC channel Freenode.
			  </p>
			  
            <p>
				There are also various grass-root communities that concentrate on some specific aspects
				or goal around the Semantic Web. Some examples:
			  </p>
			  
            <ul>
				
               <li>
				  
                  <a shape="rect" href="http://usefulinc.com/doap/">DOAP</a>: a
				  project to describe information about open-source software projects
				</li>
				
               <li>
				  
                  <a shape="rect" href="http://xmlns.com/foaf/0.1/">FOAF</a>: a project
				  to describe information about people and their social relations (see also the #foaf
				  IRC channel on Freenode)
				</li>
				
               <li>
				  
                  <a shape="rect" href="http://sioc-project.org/">SIOC</a>: a project to describe
				  information about online community sites (blogs, bulletin boards, …) and use this
				  information to connect these sites together.
				</li>
				
               <li>
				  
                  <a href="http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData" shape="rect">Linking
				  Open Data on the Semantic Web</a>: is project whose goal is to make various open data
				  sources available on the Web as RDF and to set RDF links between data items from
				  different data sources.
				</li>
			  
            </ul>
			  
            <p>
				Another source is the <a href="http://planetrdf.com" shape="rect">PlanetRDF Blog aggregator</a> that
				aggregates the blogs of a number active Semantic Web developers from around the World.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#logos">
        <title>Why has W3C developed the new cube logo?</title>
        <dc:subject>Why has W3C developed the new cube logo?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#logos</link>
        <dc:date>2007-10-21T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>HowDoIParticipate</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				The <a href="http://www.w3.org/2007/10/sw-logos.html" shape="rect">new logo</a> has been created as a high level 
				image to represent the Semantic Web, and the technology buttons have been 
				designed to create consistent branding for all of the standards that make up the Semantic Web.
				Going forwards we are planning to create pictograms for the standards for
				t-shirts, mugs, etc. In that context, you'll be seeing the familiar blue RDF triple again.
			</div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whrdf">
        <title>What is RDF?</title>
        <dc:subject>What is RDF?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whrdf</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				RDF—the <a href="/TR/REC-rdf-syntax" shape="rect">Resource Description Framework</a>—is a
				standard model for data interchange on the Web. RDF has features that facilitate data
				merging even if the underlying schemas differ, and it specifically supports the
				evolution of schemas over time without requiring all the data consumers to be changed.
			  </p>
			  
            <p>
				RDF extends the linking structure of the Web to use URIs to name the relationship
				between things as well as the two ends of the link (this is usually referred to as a
				“triple”). Using this simple model, it allows structured and semi-structured data
				to be mixed, exposed, and shared across different applications.
			  </p>
			  
            <p>
				This linking structure forms a directed, labelled graph, where the edges represent the
				named link between two resources, represented by the graph nodes. This <em>graph
				view</em> is the easiest possible mental model for RDF and is often used in
				easy-to-understand visual explanations.
			  </p>
			  
            <p>
				The <a href="http://www.w3.org/TR/rdf-primer/" shape="rect">“RDF Primer”</a> is a good material
				for further reading on RDF.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#serialization">
        <title>What formats can RDF be represented in?</title>
        <dc:subject>What formats can RDF be represented in?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#serialization</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				RDF statements (or triples) can be encoded in a number of different formats, whether
				XML based (e.g., <a href="http://www.w3.org/TR/rdf-syntax-grammar/" shape="rect">RDF/XML</a>) or not
				(<a href="http://www.w3.org/TeamSubmission/turtle/" shape="rect">Turtle</a>, <a href="http://www.w3.org/TR/rdf-testcases/#ntriples" shape="rect">N-triples</a>, …). In general it does
				not really matter which of these formats (or serializations) are used to express
				data—the information is represented in RDF triples and the particular format is only
				the “syntactic sugar”. Most RDF tools can parse several of these serialization
				formats.
			  </p>
			  
            <p>
				Compare to “numbers” as opposed to “numerals”. Numbers are mathematical
				concepts; <a href="http://en.wikipedia.org/wiki/Numeral" shape="rect">numerals</a> are a
				representation thereof using Roman, Arabic, hexadecimal, octal, etc, representations.
				Some of those representations (like Roman) may be very complicated, some of those may
				be simpler or more familiar, but they all represent the same abstract concept.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whrdfxml">
        <title>Isn’t RDF simply an XML application?</title>
        <dc:subject>Isn’t RDF simply an XML application?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whrdfxml</link>
        <dc:date>2008-01-31T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				No. The fundamental model of RDF is independent of XML. <a href="#whrdf" shape="rect">RDF</a> is a
				model describing qualified (or named) relationships between two (Web) resources, or
				between a Web resource and a literal. At that fundamental level, the only commonality
				between RDF and the XML World is the usage of the XML Schema datatypes to characterize
				literals in RDF. In fact, using <a href="http://www.w3.org/TR/grddl-primer/" shape="rect">GRDDL</a>, a way to automate 
				mappings from XML to RDF easily, many XML vocabularies can be considered applications of RDF.
			  </p>
			  
            <p>
				Note that <em>one</em> of the serialization formats of RDF is indeed based on XML
				(<a href="http://www.w3.org/TR/rdf-syntax-grammar/" shape="rect">RDF/XML</a>), and this is probably
				the most widely used format today. But others exist, see the <a href="#serialization" shape="rect">separate question on RDF representation</a>.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#weburi">
        <title>Where is the “Web” in the Semantic Web?</title>
        <dc:subject>Where is the “Web” in the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#weburi</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The Semantic Web standards follow the <a href="http://www.w3.org/TR/webarch/" shape="rect">design
				principles of the Web</a> in order to allow the growth of a planet-wide collection of
				semantically-rich data. The key element of this design is the use of Web addresses
				(URIs) to <em>name</em> things. Because the meaning of a term in a language without
				central control becomes established by its consistent use to achieve the same effect,
				and URIs are used around the World to access web pages, the Web is used to establish
				globally-shared meaning for URIs in the Semantic Web. (This is what people mean when
				they say RDF URIs are “grounded” in the Web.)
			  </p>
			  
            <p>
				As with the Web in general, this approach allows the Semantic Web to grow and evolve
				without any central control or authority, but while still maintaining as much
				consistency and authorial control as needed for particular applications or particular
				enterprises. The techniques for doing all this are still evolving, but ideally whenever
				anyone sees a Semantic Web URI they can use it in their browser and see authoritative
				documentation about its use. Moreover, whenever some software encounters a URI in a
				Semantic Web context, it can dereference it and find an ontology which precisely
				specifies how the term is related to other terms. The software may thus learn and
				exploit new terms which are synonymous with terms it already knows, or related in more
				complex and useful (but logically precise) ways.
			  </p>
			  
            <p>
				All this results in the ability to find and correctly merge data from multiple sources,
				sometimes even when they are provided with different ontologies.
			  </p>
			  
            <p>
				“In the Semantic Web, it is not the Semantic which is new, it is the Web which is
				new” Chris Welty, IBM
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whquery">
        <title>How can I query RDF data?</title>
        <dc:subject>How can I query RDF data?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whquery</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The <a href="http://www.w3.org/2001/sw/DataAccess/" shape="rect">W3C Data Access Working Group</a>
				has developed the <a href="http://www.w3.org/TR/rdf-sparql-query/" shape="rect">SPARQL Query
				Language</a>. SPARQL defines queries in terms of <em>graph patterns</em> that are
				matched against the <a href="#whrdf" shape="rect">directed graph</a> representing the RDF data.
				SPARQL contains capabilities for querying required and optional graph patterns along
				with their conjunctions and disjunctions. The result of the match can also be used to
				construct new RDF graphs using separate graph patterns.
			  </p>
			  
            <p>
				SPARQL can be used as part of a general programming environment, like Jena, but queries
				can also be sent as messages to a remote SPARQL endpoints using the companion
				technologies <a href="http://www.w3.org/TR/rdf-sparql-protocol/" shape="rect">SPARQL Protocol</a>
				and <a href="http://www.w3.org/TR/rdf-sparql-XMLres/" shape="rect">SPARQL Query Result in XML</a>.
				Using such SPARQL endpoints, applications can query remote RDF data and even construct
				new RDF graphs, without any local processing or programming burden. For more questions
				on SPARQL, see also the separate <a href="http://thefigtrees.net/lee/sw/sparql-faq" shape="rect">FAQ
				on SPARQL</a>.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#xquery">
        <title>Why not use SQL and/or XQuery to query RDF data? Why develop yet another query language?</title>
        <dc:subject>Why not use SQL and/or XQuery to query RDF data? Why develop yet another query language?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#xquery</link>
        <dc:date>2007-04-17T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				SPARQL is a query language developed for the RDF data model; queries themselves
				<em>look and act</em> like RDF. I.e., the queries are independent of the physical
				representation of the RDF data (the structure of the databases, their representation in
				an RDF/XML file, etc). If query was done via, for example, XQuery, the application
				would have to know how that particular RDF data exactly represented as RDF/XML (and
				RDF/XML is <a href="#whrdfxml" shape="rect">only one of the possible serialization</a> of the RDF
				data).
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#queryUpdate">
        <title>Can I use SPARQL to insert, delete, or update RDF data?</title>
        <dc:subject>Can I use SPARQL to insert, delete, or update RDF data?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#queryUpdate</link>
        <dc:date>2008-02-11T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>The current, standardized version of SPARQL deals only with retrieving selected data from RDF graphs. 
			  There is no equivalent of the SQL <tt>INSERT</tt>, <tt>UPDATE</tt>, or <tt>DELETE</tt> statements. 
			  Most RDF-based applications handle new, changing, and stale data directly via the APIs provided by 
			  <a href="http://esw.w3.org/topic/SemanticWebTools#head-805c63479c854babe4657d5184de605910f6d3e2" shape="rect">specific RDF storage systems</a>. 
			  Alternatively, RDF data can exist virtually (i.e. created on-demand in response to a SPARQL query). 
			  Also, there are systems which create RDF data from other forms of markup, such as 
			  <a href="http://wiki.ontoworld.org/index.php/Semantic_Wiki_State_Of_The_Art" shape="rect">Wiki markup</a> 
			  or <a href="http://wingerz.com/blog/?p=35" shape="rect">the Atom Syndication Format</a>.</p>
	
			
            <p>However, there is significant active work going on to extend SPARQL to
				support update operations. See the <a href="http://esw.w3.org/topic/SPARQL/Extensions/Update" shape="rect">SPARQL extension wiki
				page dealing with update</a> for more details. This feature is certainly one of the facilities frequently asked for
				in relation to a possible <a href="#sparql2" shape="rect">SPARQL “Next”</a> version.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#sparql2">
        <title>Will there be a SPARQL “Next”? When will feature X be standardized?</title>
        <dc:subject>Will there be a SPARQL “Next”? When will feature X be standardized?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#sparql2</link>
        <dc:date>2009-04-28T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				
            <p>The Working Group that defined SPARQL left behind <a href="http://www.w3.org/2001/sw/DataAccess/issues" shape="rect">twelve postponed
				issues</a>: potential SPARQL features that were not included in the SPARQL
				standard due to time constraints and lack of implementation experience.</p>
				
            <p>SPARQL users have asked for many extensions to the SPARQL query language.
				Some of these have been accomodated by SPARQL implementations. In an attempt
				to inform SPARQL users and to minimize implementation differences of
				non-standard SPARQL features a new 
				<a href="http://www.w3.org/2007/OWL/" shape="rect">SPARQL Working Group</a> has been set up early 2009.
				This group is busy defining the minimal number of extensions that can be done without
				backward incompatibilities and do not require a too large addition to the initial 
				version of SPARQL. The list of those features are planned to be final early summer 2009.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whontrole">
        <title>What role do ontologies and/or rules have on the Semantic Web?</title>
        <dc:subject>What role do ontologies and/or rules have on the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whontrole</link>
        <dc:date>2007-05-15T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				
            <p>On the Semantic Web both ontologies and rules are used to express extra constraints and 
				logical relationships among resources. An example for their usage is to help data integration 
				when, for example, different terms are used to describe the same thing in different data sets, or 
				when a bit of extra knowledge may lead to the discovery of new relationships.
				</p>
				
            <p>Ontologies and rules refer to two different traditions stemming from 
				logic, as developed in the past decades. Whereas ontologies are more 
				closely related to knowledge representation, and particularly to 
				description logic, rules rely more on the advances of logic programming 
				and rule based systems. 
				</p>
				
            <p>See the separate questions on <a href="#whont" shape="rect">Ontologies</a> and on <a href="#whrules" shape="rect">Rules</a>.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whont">
        <title>What are ontologies in the Semantic Web context?</title>
        <dc:subject>What are ontologies in the Semantic Web context?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whont</link>
        <dc:date>2007-05-15T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			 
            <p>
				Ontologies define the concepts and relationships used to describe and represent an area
				of knowledge. Ontologies are used to classify the terms used in a particular
				application, characterize possible relationships, and define possible constraints on
				using those relationships. In practice, ontologies can be very complex (with several
				thousands of terms) or very simple (describing one or two concepts only).
			  </p>
			
            <p>
				An example for the role of ontologies or rules on the Semantic Web is to help data
				integration when, for example, ambiguities may exist on the terms used in the different
				data sets, or when a bit of extra knowledge may lead to the discovery of new
				relationships.
			  </p>
			  
            <p>
				A general example may help. A bookseller may want to integrate data coming from
				different publishers. The data can be imported into
				a common RDF model, eg, by using converters to the publishers’ databases. However,
				one database may use the term “author”, whereas the other may use the  term
				“creator”. To make the integration complete,
				and extra “glue” should be added to the RDF data, describing the fact that the
				relationship described as “author” is the same as “creator”. This extra piece 
				of information is, in fact, an ontology,
				albeit an extremely simple one.
			  </p>
			  
            <p>Languages like RDF Schemas and various variants of OWL provide languages 
				to express ontologies in the Semantic Web context. These are stable 
				specifications, published in 2004. </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whrules">
        <title>What are rules on the Semantic Web?</title>
        <dc:subject>What are rules on the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whrules</link>
        <dc:date>2007-05-15T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				
            <p>      	
				The term “rules” in the context of 
				the Semantic Web refers to elements of logic programming and rule based 
				systems bound to Semantic Web data. Rules offer a way to express, for 
				example, constraints on the relationships defined by by RDF, or may be 
				used to discover new, implicit relationships. 
				</p>
				
            <p>
				Various rule systems (production rules, Prolog-like systems, etc) are 
				very different from one another, and it is not possible to define 
				<em>one</em> rule language to encompass them all. However, it is 
				possible to define a “core” that is essentially understood by all rule 
				systems. This core is based on restricted kind of rule, called a “Horn” 
				rule, which (like most rules) has the form “<strong>if</strong> 
				conditions <strong>then</strong> consequence”, but it places certain 
				restrictions on the kinds of conditions and consequences that can be 
				used. 
				</p>
				
            <p>
				A general example may help. While integrating data coming from different 
				sources, the data may include references to persons, their name, 
				homepage, email addresses, etc. However, the data does not say when two 
				persons should be considered as identical, although this is clearly 
				important for a full integration. An extra condition can be expressed 
				stating that “if two persons have the same name, home page, and email 
				address, then they are identical”. Such condition can be expressed with 
				Horn rules (though cannot be easily expressed by an ontology language 
				like OWL). 
				</p>
				
            <p>The <a href="/2005/rules/wg/" shape="rect">Rule Interchange Format (RIF) Working Group</a> is currently working on 
				a precise definition of this “core” Rule language, on ways to extend this rule language to various 
				variants (production rules, logic programming, etc), to exchange expression of rules among systems, 
				and to define the precise relationships of these relationships with OWL ontologies and their 
				usage with RDF triples.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#rulesandonts">
        <title>How do I know when to use OWL and when to Rules? How can I use them both together?</title>
        <dc:subject>How do I know when to use OWL and when to Rules? How can I use them both together?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#rulesandonts</link>
        <dc:date>2007-05-15T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				
            <p>RIF is not yet a W3C Recommendation (or even a Candidate Recommendation), so for now it should only be used on an experimental basis. As it proceeds to Recommendation status, however, it will be accompanied by an answer to this question, which the RIF Working Group is <a href="http://www.w3.org/2005/rules/wg/charter#owl_compat" shape="rect">chartered to produce</a>.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whinference">
        <title>What is “inference” on the Semantic Web?</title>
        <dc:subject>What is “inference” on the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whinference</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Broadly speaking, inference on the Semantic Web can be characterized by discovering new
				relationships. As <a href="#whrdf" shape="rect">described elsewhere in this FAQ</a>, the data is
				modeled as a set of (named) relationships between resources. “Inference” means that
				automatic procedures can generate new relationships based on the data and based on some
				additional information in the form of an ontology or a set of rules. Whether the new
				relationships are explicitly added to the set of data, or are returned at query time,
				is simply an implementation issue.
			  </p>
			  
            <p>
				A simple example may help. The data set to be considered may include the relationship
				<code>(Flipper isA Dolphin)</code>. An ontology may declare that “every
				<code>Dolphin</code> is also a <code>Mammal</code>”. That means that a Semantic Web
				program understanding the notion of “<code>X</code> is also <code>Y</code>” can add
				to the set of relationships the statement <code>(Flipper isA Mammal)</code>, although
				that was <em>not</em> part of the original data. One can also say that the new
				relationship was “discovered”.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whmustont">
        <title>Must I use ontologies for Semantic Web Applications?</title>
        <dc:subject>Must I use ontologies for Semantic Web Applications?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whmustont</link>
        <dc:date>2008-02-14T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				It depends on the application. <a href="#whinference" shape="rect">The answer on the role of
				ontologies and/or rules</a> includes a very simple ontology example. Some applications
				may decide not to use even such small ontologies, and rely on the logic of the
				application program. Some application may choose to use very simple ontologies like the
				one described, and let a general Semantic Web environment use that extra information to
				make the identification of the terms. Some applications need an agreement on common
				terminologies, without any rigor imposed by a logic system. Finally, some applications
				may need more complex ontologies with complex reasoning procedures. It all depends on
				the requirements and the goals of the applications.
			  </p>
			  
            <p>
				The current Semantic Web technologies offer a large palette of languages to describe
				simple or complex terminologies: <a href="http://www.w3.org/TR/rdf-schema/" shape="rect">RDF
				Schemas</a>, <a href="http://www.w3.org/TR/swbp-skos-core-guide" shape="rect">SKOS</a>, or various
				dialects of <a href="http://www.w3.org/TR/owl-ref/" shape="rect">OWL</a> (OWL Lite, OWL DL, OWL
				Full). 
				These technologies differ in expressiveness but also in complexity. Applications have a choice 
				along a range from RDF Schema for representing the simplest ontology level, to OWL Full for 
				maximum expressiveness. In addition semantic web users are encouraged to
				leverage existing ontologies where possible: e.g., SKOS for
				representing basic structures like thesauri, taxonomies or other
				controlled  vocabularies. Good places to look for existing ontologies
				are detailed <a href="#findont" shape="rect">elsewhere in this FAQ</a>.
				They also have a choice of not to use any of those; the usage of
				ontologies is <em>not</em> a requirement for Semantic Web applications.
			  </p>
			  
            <p>
				Note that there is an active area of development of defining other “profiles” of
				ontology languages targeting a minimal
				level of ontology that, in some cases, might be just a little bit more expressive than <a href="http://www.w3.org/TR/rdf-schema/" shape="rect">RDF Schemas</a>. This topic has also been taken up by
				the new <a href="http://www.w3.org/2007/OWL/" shape="rect">OWL Working group</a> (formed at the end of 2007)
				which has on its charter the development of such “profiles”.
				Also, the <a href="http://www.w3.org/2005/rules/" shape="rect">current work on rules at W3C</a> may lead, eventually,
				to the alternative of using some simple rules instead of (or as an extra to) ontologies.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whtopont">
        <title>Does the Semantic Web try to impose meaning from the top?</title>
        <dc:subject>Does the Semantic Web try to impose meaning from the top?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whtopont</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				No. What the Semantic Web technologies do is to define the “language” with well
				understood rules and internal semantics, ie, <a href="http://www.w3.org/TR/rdf-schema/" shape="rect">RDF Schemas</a>, various dialects of <a href="http://www.w3.org/TR/owl-ref/" shape="rect">OWL</a>, or <a href="http://www.w3.org/TR/swbp-skos-core-guide" shape="rect">SKOS</a>. Which of those formalisms are
				used (if any) and what is “expressed” in those language is entirely up to the
				applications. Ontologies may be developed by small communities, from “below”, so to
				say, and shared with other communities.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whgiantont">
        <title>Does the Semantic Web require everybody to subscribe to a single, predefined, giant ontology?</title>
        <dc:subject>Does the Semantic Web require everybody to subscribe to a single, predefined, giant ontology?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whgiantont</link>
        <dc:date>2008-01-22T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Obviously, that would not be feasible. If ontologies are used, they can come from
				anywhere and be mixed freely. In fact the “ethos” of the Semantic Web is to
				<em>share</em> and <em>reuse</em> as much as possible, and lot of work is done to
				semi-automatically bridge different vocabularies. Typical Semantic Web applications mix
				ontologies developed by different communities on the Web, like the <a href="http://dublincore.org/documents/dces/" shape="rect">Dublin Core metadata</a>, <a href="http://xmlns.com/foaf/0.1/" shape="rect">FOAF</a> (friend-of-a-friend) terms, etc.
			  </p>
			  
            <p>
				The Semantic Web’s attitude to ontologies is no more than a rationalization of actual
				data-sharing practice. Applications can and do interact without achieving or attempting
				to achieve global consistency and coverage. A system that presents a retailer’s wares
				to customers will harvest information from suppliers’ databases (themselves likely to
				use heterogeneous formats) and map it onto the retailer’s preferred data format for
				re-presentation. Automatic tax return software takes bank data, in the bank’s
				preferred format, and maps them onto the tax form. There is no requirement for global
				ontologies here. There isn’t even a requirement for agreement or global translations
				between the specific ontologies being used except in the subset of terms relevant for
				the particular transaction. Agreement need only be local, but adoption of vocabularies
				from existing ontologies facilitates data sharing and integration. Of course, some of the vocabularies
				may become more and more widely used and adopted, but the evolution is more bottom-up, rather than top-down.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#noTermAgreement">
        <title>People will never get common agreement on terms; won’t this lead to the failure of the Semantic Web?</title>
        <dc:subject>People will never get common agreement on terms; won’t this lead to the failure of the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#noTermAgreement</link>
        <dc:date>2008-01-22T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>The issue, referred to by this question, is that different people will not agree on exactly how 
			  to define all concepts.  Eg, while most  people have a fairly standard concept of a “dog” or a “cat”, not 
			  everyone can distinguish between a “scalar” and a “vector”, for instance.  Any computer application  
			  which tries to standardize its ontology will necessarily distort what at least some people are really 
			  trying to express; as a consequence, there will be ontological mismatches across parts of the Web designed by different people.
			  The issue is whether this may not ruin the very goals of the Semantic Web.</p>
			  
			  
            <p>However, the Semantic Web does <em>not</em> rely on having one, big, all-encompassing ontology. Instead, 
			  the Semantic Web is built up from small like-minded communities that can find agreement on terms amongst 
			  themselves. Applications, then, can and do interact without attempting to achieve global consensus.
			  There is no requirement for global ontologies: instead, an application need 
			  only map the terms relevant for a particular transaction into a common vocabulary. Of course, though 
			  agreement need only be local, adoption of existing vocabularies facilitates data sharing and integration.
			  </p>
			  
			  
            <p>Note that this issue is, essentially, the same as the one asking whether the Semantic Web requires 
			  everybody to subscribe to a single, predefined, giant ontology; see also the <a href="#whtopont" shape="rect">answer to that question</a>, 
			  including further examples.</p>
			 
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whontdev">
        <title>What is involved in developing an ontology using Semantic Web technologies?</title>
        <dc:subject>What is involved in developing an ontology using Semantic Web technologies?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whontdev</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				The real difficulty, when developing an ontology, is to <em>understand</em> the problem
				that has to be modeled and <em>find an agreement</em> on a community level. <a href="http://www.w3.org/TR/rdf-schema/" shape="rect">RDF Schemas</a> and/or <a href="http://www.w3.org/TR/owl-ref/" shape="rect">OWL</a> provide a framework to formalize those
				ontologies in a specific language; the time and energy needed to learn and use them is
				only a fraction of the time needed to develop an ontology itself, ie, understand the
				terms and the relationships of given area of knowledge and agree with your peers.
				Ontology development tools, like Protégé or SWOOP, hide most of the syntax complexity
				and let the user concentrate on the real representation issues.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#logicIncosistency">
        <title>Consequences of inconsistency in formal logic: doesn’t that ruin the Semantic Web?</title>
        <dc:subject>Consequences of inconsistency in formal logic: doesn’t that ruin the Semantic Web?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#logicIncosistency</link>
        <dc:date>2008-01-22T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>The problem referred to by this question is the fact that, in formal logic, if there 
			  is an inconsitency somewhere, then it is possible to draw <em>all</em> conclusions <em>and</em> their
			  negations. The issue is whether this would not create major difficulties on the Semantic Web.</p>
			  
			  
            <p>“Inference” in terms of the Semantic Web can be characterized by discovering 
			  new relationships (as explained <a href="#whinference" shape="rect">in the answer of another question</a>). These inferences are mostly done within a restricted, “guarded” subset of first order logic. Usually, reasoning on the Semantic Web does not use the full power of first order (or higher order) logic, and therefore avoids some of the dangerous issues that can come from an inferred inconsistency. In other words, in practice, no major difficulties can be expected.</p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whontstand">
        <title>Will W3C be standardizing any particular ontologies?</title>
        <dc:subject>Will W3C be standardizing any particular ontologies?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whontstand</link>
        <dc:date>2007-04-12T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				In general, ontologies should be created and maintained by various, specialized
				communities. The preference of W3C is to let these other communities develop their own
				ontologies; this is the case for well known ontologies like the <a href="http://dublincore.org/documents/dces/" shape="rect">Dublin Core</a>, <a href="http://xmlns.com/foaf/0.1/" shape="rect">FOAF</a>, <a href="http://usefulinc.com/doap" shape="rect">DOAP</a>,
				etc.
			  </p>
			  
            <p>
				There are cases, however, when ontologies are developed at W3C. This is the case when,
				for example, another W3C technology needs its own, specialized ontology (<a href="http://www.w3.org/TR/EARL10-Schema/" shape="rect">EARL</a> is a good example), when W3C feels that
				the existence of a particular ontology is crucial for the advancement of the Semantic
				Web, or when the community prefers to use, for example, the facilities offered by the
				<a href="http://www.w3.org/2005/Incubator/" shape="rect">Incubator Activity of W3C</a>.
			  </p>
			
         </div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#skos">
        <title>What is SKOS?</title>
        <dc:subject>What is SKOS?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#skos</link>
        <dc:date>2007-11-27T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
				The <a href="http://www.w3.org/TR/skos-reference" shape="rect">Simple Knowledge Organization System (SKOS)</a>
				is an ontology for expressing the basic structure and content of concept schemes such as thesauri,
				classification schemes, subject heading lists, taxonomies, glossaries,
				folksonomies, other types of controlled vocabularies. It provides a standard,
				low-cost way of migrating existing concept schemes to the Semantic Web, so that they can be 
				used as-is for the development of lightweight Semantic Web
				applications. SKOS is increasingly seen as a bridging technology, providing
				the missing link between the rigorous logical formalism of ontology languages
				such as OWL and the chaotic, informal and weakly-structured world of social
				approaches to information management, as exemplified by social tagging applications.         
			</div>]]></content:encoded>
    </item>
    <item rdf:about="http://www.w3.org/2001/sw/SW-FAQ#whpubldata">
        <title>Is there an uptake in public datasets for the Semantic Web? Are there major data published for the Semantic Web already?</title>
        <dc:subject>Is there an uptake in public datasets for the Semantic Web? Are there major data published for the Semantic Web already?</dc:subject>
        <link>http://www.w3.org/2001/sw/SW-FAQ#whpubldata</link>
        <dc:date>2007-11-26T00:00+00:00</dc:date>
        <dc:creator>Ivan Herman (ivan@w3.org)</dc:creator>
        <dc:author>Ivan Herman (ivan@w3.org)</dc:author>
        <dc:subject>TechieQuestions</dc:subject>
        <content:encoded><![CDATA[<div class="answer">
			  
            <p>
				Major datasets (or access to existing datasets) are created quite often these days.
				Just some examples:
			  </p>
			  
            <ul>
				
               <li>The <a href="http://dbpedia.org" shape="rect">DBpedia</a> community effort to query Wikipedia
				like a database (see also a <a href="http://www.mkbergman.com/?p=354" shape="rect">more detailed
				blog entry</a> on this project).</li>
				
               <li>
				  
                  <a href="http://www.ingentaconnect.com/" shape="rect">IngentaConnect</a> bibliographic metadata (around 200 million triples)</li>
				
               <li>
				  
                  <a href="http://www.w3.org/TR/wordnet-rdf/" shape="rect">RDF/OWL representation of Wordnet</a>
				
               </li>
				
               <li>eBusiness ontology for products and services: <a href="http://www.heppnetz.de/eclassowl" shape="rect">eClassOwl</a>
				
               </li>
				
               <li>the <a href="http://www.geneontology.org/" shape="rect">Gene Ontology</a>, to describe gene and
				gene products attributes in any organisms
				</li>
				
               <li>protein sequence and annotation data: <a href="http://www.isb-sib.ch/~ejain/rdf/" shape="rect">
				  UniProt</a>
				
               </li>
				
               <li>
				  
                  <a href="http://www.geonames.org/ontology/" shape="rect">Geonames Ontology and associated RDF
				  data</a>: geographical features (e.g., information on the city of Berlin) encoded in
				  RDF
				</li>
			  
            </ul>
			  
            <p>
				Note also that one of the <a href="http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData" shape="rect">“Community
				Projects”</a> sponsored by the <a href="sweo" shape="rect">W3C Semantic Web Education and Outreach
				Interest Group</a>, namely the <a href="http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData" shape="rect">“Linking
				Open Data on the Semantic Web” project</a>, aims at making various open data sources available 
				on the Web as RDF and to set RDF links between data items from different data sources. 
				Collectively, the datasets consist of over several billions RDF triples, which are interlinked by around 
				many millions of RDF links.</p>
			
         </div>]]></content:encoded>
    </item>
</rdf:RDF>