[sc34wg3] Topic names and occurrences in the TMDM

Lars Marius Garshol sc34wg3@isotopicmaps.org
Fri, 30 Sep 2005 11:53:08 +0200

* Jan Algermissen
| Since TMDM suggested practice seems to be to express attributes of
| subjects (age, height, eye-color, department number etc.) as
| occurrences [...]

This has been the practice in the Topic Maps community ever since XTM
1.0 was published in 2001, and was why internal occurrences were
introduced in the first place. XTM 1.0 even contains an example of
such use in 3.9.1:

  <URL: http://www.topicmaps.org/xtm/1.0/#elt-occurrence >

This is not a TMDM innovation.

| Subject Indicators and Subject Address are then, BTW, also just
| occurrences.

No, they are not. TMDM is very clear that occurrences are statements
about the subject, but these two are not. (And it's subject locator.)
They are also structurally different (they cannot be scoped, and they
cannot be reified).

| I have allways wondered what the benefit of four constructs for
| things that are just semantic variations of a basic functinality
| could be....seems awkward to have to implement basically the same
| thing four times....

Who says you have to implement it four times? Your internal model can
be simpler if you want it to be. Look at TMRM, or Q. The point is
that, as Kal says, the *semantics* matter.

Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no >