From: pat hayes (phayes@ai.uwf.edu)
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. > >Agreed! > > > 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. Pat --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
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