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RE: DDTF/layering: weak class theory seems good enough (5.3, 5.10)

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 29 May 2002 08:29:11 -0400
To: jjc@hplb.hpl.hp.com
Cc: connolly@w3.org, www-webont-wg@w3.org
Message-Id: <20020529082911L.pfps@research.bell-labs.com>

From: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Subject: RE: DDTF/layering: weak class theory seems good enough (5.3, 5.10)
Date: Wed, 29 May 2002 13:06:07 +0100

> - the layer cake diagram of Tim BL is a vision that we should not even
> attempt to take as constraining (i.e. there is no requirement for a
> clean, monotonic layering of ontology over RDFS)

I disagree with this characterisation of the majority view.  The problem is
that a same-syntax extension is not possible, unless the upper layers are
non-standard, and probably non-standard in a way different from any ever
devised before.  

> - layerings on top of RDF that do not respect RDF Model Theory are in
> anyway desirable (even if OWL didn't need it)

RDF has some very odd constructions.  Changing these constructions is
indeed desirable, in my view.  They impeed progress towards the upper
levels of the layer cake.

> I think there are two proposals that I think we can be confident would
> work: one in which all the ontology stuff is dark, and one in which no
> sets necessarily exist.

The first definitely works.  There is not yet an existence proof that the
second does indeed work, at least as an extension of the RDF model theory.

> I am worried that the position of the twenty is actually backing a
> research option - i.e. neither of those extremes is desirable. Pat seems
> to say only the lists need to be dark, Peter only seems to need the
> restrictions to be dark ... but I don't believe there have been
> proposals that have sufficient content to articulate clearly either of
> these.

I have only said that the restrictions need to be dark, not that only the
restrictions need to be dark.  It may be possible to have some of the
ontology portion be non-dark, but, again, an existence proof has not yet
been put forward, at least to my knowledge.

> In OWL1 we can choose to:
> A: not get all the set theoretic entailments we would like, but get the
> layering right
> B: get the set theoretic entailments we would like, but screw the
> layering
> C: take enough time to make a better job on the layering and get all the
> set theoretic entailments
> D: take even longer and get both the layering and the set theoretic
> entailments right.
> I think both the last two (C and D) can be postponed until OWL2 (after
> this working group).
> I personally prefer prioritizing the layering (A), since set theory is
> easier.
> Jeremy

The question is what is the correct layering.  If you mean a same-syntax
extension, then, again, that is impossible for the uppper layers without
going to a very non-standard logic.  If, however, you allow syntax
extensions, and I see absolutely no reason not to allow syntax extensions,
then the situation changes completely.  (Of course, you are still left with
dealing with the odd parts of RDF.)

Received on Wednesday, 29 May 2002 08:29:57 UTC

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