[sc34wg3] Association items

Murray Altheim sc34wg3@isotopicmaps.org
Sun, 12 Jun 2005 20:48:19 +0100

Nikita Ogievetsky wrote:
> But it is not clear from the historical use of associations, especially
> the way that they were meant to replace facets.

There's a number of opinions on this, depending on who you talk to.
If I remember correctly, Steve Newcomb recounts some of this in his
chapter in the XML Topic Maps book, then I also seem to remember
having a conversation with Martin Bryan about it. It wasn't so much
that associations were "meant to replace" facets as it was (to my
memory) that associations are able to model what facets were meant
to provide. That is, in the simplified model of "facets" as defined
(minimally) in ISO 13250:2000.

> I wonder if facets should be considered to be brought back into XTM.

If you mean modify the XTM syntax to provide for them, I must agree
with the above-stated sentiments that there's no need. From the simple
facets-as-properties perspective, you can do anything ISO 13250 facets
can do with the current syntax. If you mean more of the complexities
of a different definition of facets, as perhaps in Faceted Classification,
you can do any of this using the current syntax and a PSI set. I'm doing
that now in Ceryle, for example (and in fact use it quite extensively as
both part of my base ontology and functionally within the software too).

I seem to remember that Lars Marius, myself and a few others had an
extended discussion of this a few months ago on either this or the
topicmapmail list.

> On the other hand, even "monadic" associations (re: Murray's posts on the
> other sub-thread) have a few topics related - if you count association type
> and scope.

As I mentioned in one of my previous posts, this is determined by
whether you want to bring the things in the model you're discussing
up to the full status of "entity" (Topic), or if they should be
modeled as properties (Topic characteristics). Association type
and scope are not full entities (Topics) in XTM, though they do
potentially link to them, as you say. These are, however, both
optional in XTM 1.0. I realize that Lars Marius has argued that
association type (along with other things) should not be optional
in XTM, whereas I would suggest that XTM be left alone and push
this kind of thing into a proper constraint language operating at
a higher schema level -- the XTM DTD is really only meant to
express syntax-level constraints.


Murray Altheim                          http://www.altheim.com/murray/
Strategic and Services Development
The Open University Library
The Open University, Milton Keynes, Bucks, MK7 6AA, UK               .

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