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

Bernard Vatant sc34wg3@isotopicmaps.org
Wed, 20 Nov 2002 14:43:55 +0100

A number of issues with RM4TM have been discussed lately in quite a disorder, and the
threads have become very difficult to follow. So I will start a few threads corresponding
to identified issues. This one is about role players as sets.

I will start from concerns expressed by Graham, that do no seem to have been addressed so

[Graham Moore]
> I appreciate that RM does not subscribe to any mathematical set model ...

Why so? My maths background tends to make me disagree with that.
I would like the RM to stand on a strong mathematical model, grounded in set theory.
That is the aim of the HG4TM proposal (see previous message)

> ... but i wonder about when do individuals become sets?

Hmm. Strange question indeed. Individuals do not "become" sets.
As I understand it, in RM4TM, it would be consistent for the role player to be *always* a
set, including the empty set, or a set with a single element.

> I'm not sure I found it but if I have two assertions in different maps where:

> graham worksfor empolis gmbh
> graham worksfor empolis uk

The role players of the "employer" role should be respectively in that case {empolis gmbh}
and {empolis uk}

> and I merge them what happens?

The new role player is the reunion of the two sets.

> is it now true that
> graham worksfor [empolis gmbh, empolis uk]

IMO yes, with correct set notation please :))
{empolis gmbh, empolis uk}

> How does this differ from the example bernard gave regarding his set of children?

Apparently no difference. I have to be resigned to be the father of a set of children.

That is the way I understand the logic of RM4TM. But if it is, we need a specific
representation of the set-member relationship.
Otherwise, what are the role players in the set-member assertion? We have a recursivity
problem here ...