4.3 XML Topic Maps 77
To get this kind of list, one only needs to say that therdf:ParseTypeif the
property value isCollection. This is much simpler than using a container.
Summary
- RDF is a framework for representing explicit many-to-many relationships
(called properties) between web-based resources and data.
- The semantics of RDF is defined by RDF graphs.
- RDF has built-in inference rules for subclasses, subproperties, domains
and ranges.
- Inference is a powerful feature, but one must be careful when using it.
- Conversion from XML DTDs or schemas to RDF cannot be automated.
- Ordered structures can be defined using RDF containers and collections.
4.3 XML Topic Maps
The XML Topic Maps (XTM) language is another XML-based ontology lan-
guage that has a very different history and semantics than any of the other
XML-based ontology languages (XTM 2000). XTM provides a model and
grammar for representing the structure of information resources used to de-
fine topics, and the associations (relationships) between topics. Names, re-
sources, and relationships are characteristics of abstract subjects, which are
calledtopics. Topics have their characteristics within scopes, that is, the lim-
ited contexts within which the characteristics of topics apply.
Consider the Medline citation shown in figure 4.5. When written in XTM
it would look something like this:
<topic id="PMID10476541">
<instanceOf><topicRef xlink:href="#MedlineCitation"/></instanceOf>
<baseName>
<baseNameString>Breast cancer highlights</baseNameString>
</baseName>
<occurrence>
<instanceOf><topicRef xlink:href="#html-format"/></instanceOf>
<resourceRef
xlink:href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?..."/>
</occurrence>
</topic>
