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Re: LBase in the RDF Semantics Doc

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 15 May 2003 08:36:41 -0400 (EDT)
Message-Id: <20030515.083641.68937503.pfps@research.bell-labs.com>
To: sandro@w3.org
Cc: www-rdf-interest@w3.org

From: Sandro Hawke <sandro@w3.org>
Subject: Re: LBase in the RDF Semantics Doc 
Date: Thu, 15 May 2003 05:15:09 -0400

> 
> 
> > The RDF Semantics document specifies the formal semantics of RDF(S).  It 
> > includes an informative appendix
> > 
> >    http://www.w3.org/TR/rdf-mt/#Lbase
> > 
> > which restates the semantics in the form of a small set of axioms.  The 
> > intent is that this representation is easier to understand.
> > 
> > RDFCore have had a last call comment suggesting this appendix be removed:
> > 
> >    http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0092.html
> > 
> > It would be helpful in resolving this comment, for the WG to have feedback 
> > on whether or not folks find this appendix useful.
> 
> I found them fun and interesting, and I wrote an LBase parser partly
> so I could play with them.  More to the point, on some matters I find
> them the easiest-to-understand source.  I think Peter's comment above
> is a bit silly, since I can't imagine anyone who could understand the
> axioms who wouldn't assume the bit he suggests is missing.   
> 
>      -- sandro

Definitely something is missing, but which something?  There are many
somethings that could be added, including statements of the following sort:

1/ The translation preserves satisfibility in RDF/RDFS/D.
2/ The translation preserves RDF/RDFS/D entailment.
3/ There is a one-to-one correspondence between RDF/RDFS/D-models of RDF
   graphs and LBase models of the translation of the RDF graph plus the
   RDF/RDFS/D axioms.  
4/The correspondence in 3 preserves intended meaning (for some notion of
  intended meaning).

I'm pretty sure that neither 2 nor 3 is correct for any of RDF, RDFS, or D.
1 might be correct for RDF and RDFS, but I'm not even sure of that.  (I
could probably convince myself one way or the other with not too much
effort.)  However 1 is not very useful as satisfiability is not a
particularly useful notion in RDF.  4 is definitely incorrect for any
reasonable notion of intended meaning.

Peter F. Patel-Schneider
Bell Labs Research
Lucent Technologies
Received on Thursday, 15 May 2003 08:36:56 GMT

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