Topic Maps
I’ve been reading about Topic Maps, an ISO standard that has been augmented with an XML representation.
Topic maps are very similar to the RDF, in that they are all about graphs of topics (representing real-world subjects) connected with associations. The difference is that the Topic-maps paradigm seems easier to understand. Maybe its because they draw a distinction between the topics and the subjects they stand in for, whereas RDF tends to conflate the two. Or maybe its the way a few important relationships (like occurence and instanceOf) are treated specially in topic maps, which makes maps a little less bewilderingly generic.
Topic maps have a system of using
URIs
to stand in for particular abstract subjects.
Separate topic maps using the same URI
http://www.topicmaps.org/xtm/language.xtm#en
as the subject indicator for the English language
know they are referring to the same thing.
When they are merged, the corresponding topics will be combined
automatically. One of the activities of various topic-map
committees is creating published subject indicators for
various generically useful types of topic, in order to promote
interoperability between topic maps.
Other (meta)data systems use URIs to represent subjects:
RDF does (using a
weird convention where XML element-names turn in to URIs),
RSS 0.9x/2.0 does
(inasmuch as category names may be interpreted
relative to a domain specified by a URL). It would
be kind of cool if we could all agree to use the same
subject identifiers, so our various efforts interoperate as much
as possible.