Re: Urgent! Semantic question about rdfs:domain.

From: pat hayes (
Date: 04/25/01

>On April 25, pat hayes writes:
> > >Pat, I believe the current semantics are correct. The RDF Schema Spec
> > >(sect. 3.1.4) says that rdfs:domain is "used to indicate the class(es)
> > >on whose members a property can be used." To me, this indicates that an
> > >instance of the class does not have to have a value for that property,
> > >i.e., that there could be some Animals for which there is no hasParent
> > >property, but any thing with a hasParent property must be an Animal.
> >
> > Interesting. To me, that form of words suggests the oppposite
> > interpretation. (If a property has no value for some individual then
> > it cannot be "used" on that individual, surely? If it gets used, what
> > is the value of the property?)
> >
> > The real moral is that vaguely worded specifications are worse 
>than useless.
> > OK, but I will take your advice. My problem now is that I don't feel
> > competent to rewrite the walkthru explanations, as I no longer feel
> > that I really follow the intended interpretation of properties and
> > domains. As far as I can see, with this interpretation, there is
> > never any point in declaring a domain or a range. Those statements
> > have no utility, since they do not allow a reasoner to draw any
> > conclusions.
>I don't quite understand this. If Range(P,C) and P(x,y) then the
>reasoner can infer C(y) - and similarly for Domain.

Yes, true. I spoke carelessly. I should have said that they do not 
allow a reasoner to draw any conclusions about the classes, ie other 
than by mentioning individuals. I was thinking of the fact that if 
one were to alter all domains and ranges to Thing, everything would 
stay true.

>As I said in my
>other email on this subject, range and domain can simply be seen as
>syntactic sugar for inclusion axioms.

Yes, that is a very helpful way of explaining them, thanks.

>This kind of axiom can (as Jeff
>also pointed out) be used to state either/both the universal and
>existential forms of restriction. They offer just as much/little
>potential for inference as any other kind of axiom, don't they?

I suspect that my initial failure to grasp this arises from a 
difference in cognitive style between class/property thinking and 
traditional logical thinking. I see now that I have been consistently 
thinking in terms based on old intuitions which I learned originally 
from category theory, so that I have been thinking of a property as a 
kind of morphism. That is not the right way to think here.

OK, thanks for the input. I also see that there are a lot more 
conceptual safety guards that need to be put into the walkthrough, 
and will try again to write them up.


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