From: pat hayes ([email protected])
Date: 08/28/01
(Im sending this to the entire JC in case anyone has anything to say
about it. If you aren't interested, please ignore it, thanks.)
Re. today's telecon, I would like to bring up the question of the
connections (or lack) between the two issues of whether 'subclass' is
understood to mean proper subclass, and whether subclass loops should
be illegal. I confess to having conflated these in my mind, largely I
suppose because I couldn't imagine any reason to forbid subclass
loops other than because 'subclassOf' is understood to hold only
between proper subclasses.
Since Peter, Ian and others all joined in a chorus of dismay when I
said this, and since this assumption is currently embedded in the
draft RDF/S model theory, I would like to pursue it a little more.
1. What reason can there be to forbid subclass loops, other than
subClassOf being understood to mean proper subclass?
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?
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.
Pat
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