[topicmapmail] Reification and Type Instance

[Steve Pepper]

| * Robert Cerny
| >
| > I have a question regarding the TMDM: If i reify a typed statement,
| > is the resulting topic an instance of the type of the statement?

* Lars Marius Garshol
| 
| This came up a couple of times in ISO meetings, but was never really
| resolved, partly because in the contexts where it came up, it didn't
| need to be.
| 
| ...
| 
| I can't really find any good reason why it shouldn't be the same
| type. If anyone can I'd be interested to hear it. (Borislav?)

I certainly can't, but...

I have long felt this to be an unresolved issue that ought to be addressed,
and I was hoping that the "correct" answer would fall out of the work on the
mapping from the TMDM to the TMRM.

I agree with Lars Marius that both the association and the topic that reify
it represent the same thing and should therefore be instances of the same
class. The only thing that worries me is the possible implications for
existing tools and applications.

Assuming we decide to state explicitly that the type of the association
becomes the topic of the reifying topic, a number of questions arise:

* Does the inverse apply? That is, does the topic type of the reifying
  topic become the association type of the association? If so, what
  happens if the topic is an instance of multiple types (since an
  association type cannot have multiple types)? In particular, what
  happens when there are type hierarchies? (Note: I would have a lot
  of use for the equivalent of rdfs:subpropertyOf.)

* Is the topic map author required to express the type-instance
  association, between the "association type topic" (e.g. employed-by)
  and the reifying topic, explicitly? (This would break backward
  compatibility with existing documents.)

* Is a Topic Maps processor required to instantiate the (implicit)
  type-instance association explicitly? (This would break backward
  compatibility with existing processors.)

* Do TMQL and TMCL processors have to infer the association? (This
  needs to be resolved PDQ, before these standards go to FCD.)

Steve