Re: Where DAML+OIL deviates from the RDF-Schema spec.

>On Mon, 5 Mar 2001, Peter F. Patel-Schneider wrote:
>
> > Sorry I should have made my comments more precise.
> >
> > However, I think that my point still stands.  There is no statement in RDFS
> > that subClassOf is < (strict subset) and not <= (non-strict subset).  In
> > the absence of such a statement, I think that the reading for subClassOf
> > should be taken to be permissive.
>
>No, they don't say that subClassOf implies strict subset. But they say the
>everything else, and the interpretation is quite clear to me.

You seem to have an ability to interpret texts which rises above mere 
mathematical competence.

> > It turns out, of course, that RDF and RDFS have no means of creating two
> > classes that are equivalent, aside from subClassOf cycles, so, perhaps, the
> > prohibition on cycles could be inferred to mean strict subset.
>
>The spec says that
>
>	"rdfs:subClassOf property is transitive"

SubClass is transitive whether it is understood inclusively or 
narrowly (ie as < or <=), so this doesn't help.

>and a line or so below that they continue
>
>	"A class can never be declared to be a subclass of itself, nor
>	of any of its own subclasses. Note that this constraint is not
>	expressible using the RDF Schema constraint facilities
>	provided below, and so does not appear in the RDF version of
>	this specification given in Appendix A"
>
>It is obvious for me what this means, and why it is there.

It is not obvious to me. If subclass is understood narrowly (<) then 
it would be nonsensical to assert that a class was subclass of 
itself. If it is understood widely (<=) then it would be vacuous to 
assert that a class was a subclass of itself. Either way, it would be 
rational to prohibit the declaration. So nothing whatever can be 
clearly inferred from this part of the spec (like a good deal of the 
rest of it.)

> > However, this is, in my opinion, ``reading between the lines'', and
> > any clarification would be a change.
>
>Well, we agree on one thing, namely that this could have been
>formulated more clearly. Anyway, only a negligible amount of reading
>between the lines is required to spot the difference between daml and
>rdfs in this respect. As a first approximation I'd say that this
>amount could be regarded as zero.

By documentation standards I am used to, the amount of "reading 
between the lines" that is required is way too high. Which is a pity, 
as it is not really hard to make the meaning clear. For example, in 
order to say that X is the case, it is good practice to say that it 
is the case, rather than say that it is not kosher to say that it is 
not the case.

Pat Hayes

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Received on Monday, 5 March 2001 14:38:12 UTC