[sc34wg3] TMCL 6.7 Overlap Declaration, Global Validation Rule
Lars Marius Garshol
larsga at garshol.priv.no
Sat Jun 20 04:03:16 EDT 2009
* Patrick Durusau
> Err, but isn't the "overlap" of a supertype/subtype relationship
> two topics different from say the overlap of a topic being of type
> father and also of type employee?
It's different, but the two are related.
> That is to say that shouldn't I be able to distinguish between saying
> that t2 may be a subtype of t1 versus t2 may overlap with t1?
You are able to distinguish, of course, because they are different
association types. So there's no confusion of the two.
> As I read the declaration and global validation rule, those two cases
> are being treated as the same?
No, what the rule is saying is that the following (assuming it's a
complete topic map) is not OK:
lmg isa person; isa creature.
Because unless explicitly declared to be OK, two topic types are not
allowed to overlap.
However, the following *is* allowed:
person ako creature.
lmg isa person.
Even though by the semantics of supertype-subtype (ako) lmg is now
both a person *and* a creature.
The reason we have that extra check in the global validation rule is
that supertype-subtype states not just that the sets of instances
overlap, but that in fact one is a subset of the other. (Every person
is a creature, is what the subtyping is saying.)
So you could say that supertype-subtype implies an overlap, but has
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