I have been thinking about RDF support on Ontopedia PSI server for quite some time. Semantic Technology Conference that I attended this spring gave me some new ideas in this direction. I decided to follow recommendations from Eric Miller’s and David Wood’s presentation “Persistent Identifiers for the ‘Real Web'” regarding PURLs (Persistent Uniform Resource Locators). Ontopedia PSI server was extended to handle PURLs

Each Published Subject Identifier (PSI) on http://psi.ontopedia.net has an equivalent PURL on http://purl.ontopedia.net. For example, http://psi.ontopedia.net/TMRA_2008 has the corresponding PURL http://purl.ontopedia.net/TMRA_2008. What happens when we type in our browser PURL http://purl.ontopedia.net/TMRA_2008? Ontopedia PURL server returns HTTP code 303 “See Other” with “Location” header set to http://psi.ontopedia.net/TMRA_2008.

For RDF-based applications, code 303 is an indication that URI does not correspond to a “digital resource”. Web browsers will automatically jump to http://psi.ontopedia.net/TMRA_2008 which will provide nice subject/resource description.

When we need to export RDF assertions from Ontopedia, we can do something like this:

<rdf:Description rdf:about="http://purl.ontopedia.net/TMRA_2008">
      <rdfs:label>
           TMRA 2008 (Topic Maps Research and Applications  Conference)
      </rdfs:label>
      <rdfs:comment>
               Fourth International Conference on 
               Topic Maps Research and Applications
       </rdfs:comment>
       <rdf:type rdf:resource="http://purl.ontopedia.net/Conference"/>	
</Definition>	

In topic maps-based version we can have:

<topic id="id_98c49a0d3d87f067a4ba13b6d2f6d086">
	<subjectIdentifier href="http://psi.ontopedia.net/TMRA_2008"/>
	<instanceOf>
           <topicRef href="http://psi.ontopedia.net/Conference"/>
        </instanceOf>
	<name>
	   <value>
              TMRA 2008 (Topic Maps Research and Applications  Conference)
           </value>
	</name>
	<occurrence>
            <type>
	        <topicRef href="http://psi.ontopedia.net/Description"/>
            </type>
            <resourceData>
                      Fourth International Conference on 
                      Topic Maps Research and Applications
            </resourceData>
	</occurrence>
</topic>

RDF-based version uses PURLs and Topic Maps-based version uses PSIs for identification of subjects/resources.

Reference:

Persistent Identifiers for the ‘Real Web’, David Wood, Eric Miller, May 2008, PDF