RE: Linkbases, Topic Maps,and RDF Knowledge Bases -- help me understand, please

[Michael Champion <mike.champion@softwareag-usa.com>]

Well, this has been an enlightening thread!

So, RDF is in some sense the most "low level," and there are well-respected
mappings from XTM to RDF and XLink to RDF.  So RDF is presumably rich enough
to cover the others, but we can certainly imagine XLink and/or XTM providing
more conveniently useful syntax/semantics for their more specialized
purposes.  Right?

So my next question is when one or  another is most useful/appropriate.
Does anyone have some use cases to illustrate when it makes more sense to
use XLink (with metadata, not as simple physical links) vs XTM vs raw RDF to
solve a real world problem?

Getting into dicier territory, I see that RDF and XTM, and RDF and XLink can
peacefully co-exist (or coop-etate, if that were a word) with one another.
How about XLink and XTM?  From John Cowan's reply it would seem as though
XLink+RDF covers the same territory as XTM:
> 2) XLink expresses *multi-way* relations (with role labels) between
> resources...
> 3) XTM expresses multi-way relations (with role labels) between
> *topics*, where topics represent subject matters, which may be either
> themselves resources or non-addressable objects (like people) who can
> be described by resources.

*if* RDF "resources" could be either "relations" or "topics", anyway.

So, does the world need all three?  Just RDF?  RDF+XLink? RDF+XTM?

Given the fragmentation of the XTM effort into TopicMaps.net and
TopicMaps.org (not to mention whatever ISO is doing), is there good reason
to believe that the various conceptions of XTM will interoperate? What's the
"executive summary" for why a real-world company would want to wade into
that mess *if* RDF+XLink can cover the same territory?

I know that some of these are probably stupid questions/observations, but I
think there are a lot of people just as confused about this stuff as I am,
so any clarification will be appreciated.