Re: Asserting subclasses of open ranges or domains

Hi Heiko

 Indeed, but this is exactly what is *not* wanted. We don't want to
> *restrict* the range to those classes, only explicitly *allow* them.
>
> I do not quite get this point. If the range is not restricted, then
> everything is implicitly allowed.
>

Yes, it is in the current state of affairs. But as DC comments puts it, the
range is not restricted not because it is by nature completely open, but
because DC doesn't know what the restrictions should be. So it's open
default of better definition.

What extra information is provided by explicitly allowing something?
> Consider the two statements "Books can be about every topic" and "Books can
> be about every topic and about dinosaurs" - aren't they equivalent? Or did I
> miss something here?
>

Yes, in the current stae of affairs, you're right, from a purely logical
viewpoint, nothing is added by specifying subclasses of the range.  Let me
take another example. Suppose you want to set an ontology of home
appliances. You define a class "Home" and a property "hasAppliance".

Of course you can define the range of this property as "DomesticAppliance",
but you don't give any necessary condition for this class, because you don't
want to preclude any kind of stuff one can invent there. So this class has a
quasi tautological definition, it is the range of "hasAppliance". No more,
no less.

Now I can, not restrict this class, but say which kind of stuff is currently
considered as domestic appliance. So I will define "WashingMachine",
"HomeCinema", "BathTub" and whatever you like as subclasses of
"DomesticAppliance". In short I have a list of sufficient conditions for
this class, but no proper necessary conditions, beyond the tautological fact
of being the value of "hasAppliance". Sure enough, if the ontology had been
set a century ago, new subclasses would have emerge since, and an ontology
set today does not want to preclude whatever the 21st century will bring
about in this domain.

We could as well define a tautological class dcterms:Topic as the range of
dcterms:Subject, and assert only subclasses.

Is that clearer?

Bernard

-- 
Bernard Vatant
Senior Consultant
Vocabulary & Data Engineering
Tel:       +33 (0) 971 488 459
Mail:     bernard.vatant@mondeca.com
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