[sc34wg3] RM4TM issue : is role player always a set?

Jan Algermissen sc34wg3@isotopicmaps.org
Sat, 23 Nov 2002 15:16:09 +0100

Lars Marius Garshol wrote:

> * Bernard Vatant
> |
> | Otherwise, what are the role players in the set-member assertion? We
> | have a recursivity problem here ...
> * Steven R. Newcomb
> |
> | How is there a recursivity problem?  Can't a set be a set of sets?
> Sure, but if role players must always be sets and sets are composed
> from assertions you never get to the actual role players because a
> recursive infinity of sets containing more sets gets in the way.

The RM does not say that role players must always be sets. In terms of the
RM role players are subjects, nothing more. Whether those subjects are 'individuals'
or sets is entirely in the realm of the governing TM application. 

So, if you 'lookup' the player P of the Role R in an assertion of type T, you might
wonder: How do I know (in terms of the 'world outside the RM', not at the RM level)
if P is what I want or if P is actually a set of role players and I need to lookup the
members of that set to get to the sujects that play the role in 'my' world ?

The answer to this is in the semantics of the assertion type.

(Example: Is the player of the role class in an XTM 1.0 class-instance association a set
 or is it an individual ?) 


> --
> Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
> ISO SC34/WG3, OASIS GeoLang TC        <URL: http://www.garshol.priv.no >
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Jan Algermissen
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