Re: presenting data models in RIF

> 
> Michael Kifer wrote:
> > Following up on the issue of whether RIF needs its own subclassOf thingie,
> > I would argue that in order to support exchange of data models (strongly
> > argued for by Gary and, as I understood at the last f2f, favored by
> > Christian)
> 
> and objected to by me as being out of scope of RIF

Not clear how you determined that. Others seem to feel it is not out of scope.

> > we also need a minimalistic way to specify domains and ranges.
> > Similar to RDF but, again, without RDFS's ad hoc assumptions (about
> > the globality of definitions, etc.).
> 
> They are not ad hoc (and continually sniping in this way is not 
> particularly helpful).
> 
> > As in the case of the rif:subclassOf relationship, RDFS and other systems
> > will be able to map their models into RIF and thus present (much of)
> > them for exchange.
> > 
> > What I have in mind is, again, minimalistic and shared by all languages
> > I know of. We need constructs like
> > 
> > abc[foo => xyz] or (abc[foo rif:hasType xyz], if you wish)
> > 
> > which say that class abc has a property foo. For any object in abc, the
> > value of this property must be a member of class xyz.
> > The semantics will support only the following axioms:
> > 
> > Inheritance:
> >     ?Cl[?Prop => ?Type] <- ?Cl rif:subclassOf ?SC and ?SC[?Prop =>?Type].
> > 
> > Relaxation:
> >     ?Cl[?Prop => ?Type] <-
> >                     ?SubType rif:subclassOf ?Type and ?Cl[?Prop =>?SubType].
> 
> No implied constraint checking?


Constraint checking is orthogonal to this.  We did not get to talk about
constraints yet.

In due time, I would have specified a simple model theory.  I would not
leave such things to be "implied" in RIF.


> > One of the problems in RDFS is that a statement like ``foo rdfs:range bar''
> > says that 'bar' is always the range of 'foo'. One cannot say that in one
> > class the range of foo is bar, but in some other class it is something else
> > (perhaps completely unrelated to bar). Ditto with rdfs:domain.
> 
> Of course you can express such "local" range axioms in OWL.

So what? OWL is not part of RIF and we have not even discussed on how to
deal with it in RIF.

This kind of approach will lead to a hodge-podge of techniques pulled out
of different languages and tied together with a rubber band.


> > Such global scoping is a no-no for OO languages. 
> 
> Given OWL then the global/local question is a non-issue.
> 
> I would have thought the more substantive difference is that in OO 
> languages these are purely schema constraints and don't sanction 
> inferences as they do in the ontology languages. Furthermore OO 
> languages make a disjointness assumption between non-inheriting classes 
> which makes such range declarations useful as constraints in a way that 
> they often aren't in ontologies.

I have not got to talk about the semantics of the type specifications.
True, in OWL these are not constraints, but people have also worked on
frameworks in which OWL axioms are used as constraints. So (unlike a few
months ago), I will not to push this point too far.

> > In particular, for PR
> > languages whose data model is based on Java. But with the above model, one
> > could state, say,
> > 
> > Person[name=>PersonName].
> > Dog[name=>String].
> > PersonName[first=>String, last=>String].
> > 
> > without problems. Here the range of name on objects in class Person is one
> > thing and on objects in class Dog some other thing.
> > 
> > 
> > RDFS and other systems can be directly mapped into the above model. To
> > capture RDFS semantics, one would add additional axioms. For instance, if
> > we add the class of everything, Object, then the globality of rdfs:range
> > and rdfs:domain are captured by these axioms:
> > 
> > Object[?P => ?T] <- ?P rdfs:range ?T.
> 
> But any system which implements your => by mapping this to OO style 
> constraints would be unable to implement such a rule.

I fail to understand you here.

> Furthermore your inheritance/relaxation semantics are not directly 
> sanctioned on rdfs:domain/range (though this would only be an issue if 
> the rdfs:range mapping were two way).

I thought it is. It is strange that this standard axiom of any type
theory is not part of the RDFS semantics.


	--michael  


> Dave
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Received on Thursday, 16 August 2007 21:22:55 UTC