Re: subclass loops, proper subclasses and so on

From: pat hayes (
Date: 08/29/01

> >
> > 1. What reason can there be to forbid subclass loops, other than
> > subClassOf being understood to mean proper subclass?
>There is a modelling issue here, one that has very little to do with
>semantics, and much more to do with pragmantics.  Consider it in the same
>class as forbidding incoherent class definitions.

OK, I get the point (and Mike's related points). Indeed I wasn't 
thinking pragmatically :-)

> > 2. Suppose Subclass is the subclass relation, Psubclass the
> > proper-subclass relation, and R is any binary irreflexive relation
> > between classes; then (R intersect Subclass) = (R intersect
> > PSubclass). From which is follows that if some formal relation symbol
> > on classes is loop-free, then if it can be interpreted as meaning
> > subclass then it can also be interpreted as meaning proper subclass,
> > without changing the truthvalues of any expressions in the language.
> > So, what justification can there be for asserting that
> > rdfs:subClassOf does *not* mean proper subclass?
>I don't see how this can be true.
>Suppose R is ``has a different ID than'',

That is not an irreflexive relation on classes, since the same class 
may have two distinct IDs (ie two IDs may denote the same class.)

> > Thanks for any input/feedback. As the RDFCore WG is on the very edge
> > of adopting the model theory as a working draft, i would greatly
> > appreciate any feedback asap, so we don't go public with a major bug.
>If RDF(S) was to exist in isolation then these issues would not matter
>nearly so much.  However, if RDF(S) is supposed to be *the* foundation for
>the semantic web it *must* be amenable to extension, and issues such as
>this have to be considered in the context of more-expressive formalisms.

Right, point taken and I (now) agree.


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