Re: same-syntax extensions to RDF

From: Sandro Hawke <sandro@w3.org>
Subject: Re: same-syntax extensions to RDF 
Date: Sun, 19 Dec 2004 21:20:10 -0500

> 
> "Peter F. Patel-Schneider" <pfps@research.bell-labs.com> writes:
> > My understanding of the problem was to write extra semantic conditions on
> > RDF(S) interpretations, and thus generate an embedding/encoding of binary
> > first-order logic into a semantic extension of RDF(S).  You can't extend
> > the syntax at the same time, however, which means that you have to encode
> > formulae as triples somehow, and these triples retain their RDF(S) meaning.
> > 
> > However, it doesn't seem to me that Sandro has the same understanding.
> 
> No, that's exactly what I want, too.

OK.  However, the (best) part of FOL is entailment.  If you haven't
captured that, then you havn't captured FOL, and it didn't seem as if that
is what you were goind.

> I would also like the whole exercise to be, in the end, simple enough
> that the community interested in rule languages and RDF can be
> comfortably with the results.  I keep hearing about projects using RDF
> encodings of Horn or FOL, and they turn out to have either unclear or
> inconsistent semantics.  If we're going to move to a standard here, it
> would help to clear up whether it is possible to do this kind of
> encoding properly.  I can't imagine, for instance, that the approach
> taken by SWRL 0.6 would ever be approved in a W3C Recommendation, for
> the reasons I outlined in the team comment [1].

Well, here we have a distinct disagreement.  My view is that even if you
actually succeed, the result will not be worthwhile.  

Consider the case of OWL.  Through much effort, OWL is a same-syntax
extension of RDFS.  However, there are differences between this version of
OWL and the DL (i.e., more-or-less FOL) version of OWL, which is not great.
I expect that even a (mostly) successful effort of encoding FOL in RDF will
have similar divergences from "the one true FOL".

Further, writing parsers for the RDF/XML syntax of OWL is a royal pain.
(Yes, I did say parser.  An RDF/XML system is really only a tokenizer for
OWL.)  Having to write such parsers eliminates any potential benefit
associated with having one Semantic Web "language".

> If Peter can convince me that it's not possible to write the desired
> semantic condition, I can help him convince others that a different
> path needs to be taken for rule languages.  If I can convince Peter it
> *is* possible (and we figure out how onerous it is), then a standard
> can use it (or not, but because the difficulty has been actually
> weighed).
> 
> Unfortunately, I can't just hand Peter the desired semantic
> conditions.  I don't really know how to write them in the formalism of
> RDF Semantics [2].  My understanding is that Peter doesn't either and
> suspects it's not possible to write them.

Well, I at least worry that it is not possible to do this extending in a
reasonable manner.  (I certainly don't view using strings to encode
sentences as being in a reasonable manner.)

[...]

>        -- sandro

[...]

peter

Received on Monday, 20 December 2004 13:29:50 UTC