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Re: Peter's objection to the RDF(S) rules

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 08 Oct 2003 10:40:48 -0400 (EDT)
Message-Id: <20031008.104048.42022689.pfps@research.bell-labs.com>
To: phayes@ihmc.us
Cc: w3c-rdfcore-wg@w3.org

From: pat hayes <phayes@ihmc.us>
Subject: Re: Peter's objection to the RDF(S) rules
Date: Wed, 8 Oct 2003 09:35:34 -0500

> >From: Dan Connolly <connolly@w3.org>
> >Subject: Re: Peter's objection to the RDF(S) rules
> >Date: Mon, 06 Oct 2003 19:20:32 -0500
> >
> >>  On Mon, 2003-10-06 at 19:03, pat hayes wrote:
> >>  [...]
> >>  > in our case,
> >>  > the RDF(S) rules transform RDF(S)-entailment into simple entailment,
> >>  > so that  S rdf-entails E iff you can derive an S' from S by using the
> >>  > rdf rules such that S' simply entails E; but we don't give rules for
> >>  > simple entailment itself.
> >>
> >>  Yup, that's how I understand it.
> >>
> >>  I had to scratch my head a bit the first time I thought
> >>  hard about this, but I'm quite content with it.
> >>
> >>  [...]
> >>
> >>  --
> >>  Dan Connolly, W3C http://www.w3.org/People/Connolly/
> >
> >If this was indeed the case then I would not be worrying so much about the
> >situation.  It appears to be the case for RDF entailment, but the RDFS
> >entailment rules are still incomplete.  The RDFS entailment rules fail to
> >reduce RDFS entailment to simple entailment.
> 
> Are you referring to the restriction to consistent antecedents? 

Yes.

> If 
> so, the quick-patch correction (ie the restatement of the lemma with 
> this restriction) was made a while back, and in response to your 
> recent suggestion for a test case I have added some more explanatory 
> prose drawing attention to the issue, with an example of a canonical 
> inconsistency.
> 
> The text of the paragraph is as follows (just after the statement of 
> the lemma in section 7.3) :
> 
> "
> The restriction to rdfs-consistent antecedents is required in order 
> to rule out cases where an rdfs-inconsistent set of graphs 
> rdfs-entails any graph, including graphs which are syntactically 
> unrelated to the antecedent. Those cases are not covered by this 
> lemma. In order to be complete in this case, a set of rules would 
> need a clear syntactic criterion for recognizing inconsistency, and a 
> rule which allowed the inference of any triple from a graph 
> containing such a contradiction. In the case of RDFS, the appropriate 
> syntactic signal of an inconsistency could be the derivation of a 
> graph containing the following triples:
> 
> xxx rdfs:subClassOf rdfs:Literal .
> aaa rdfs:range xxx .
> yyy aaa lll .
> 
> where lll is an ill-typed XML literal.
> "
> 
> The undesireability of having rules which generate arbitrary 
> conclusions is discussed elsewhere in the document.

I do not consider this to be an adequate description of how to recognize an
rdfs-inconsistent graph.  I have proposed what I consider to be adequate
coverage of this issue in a previous email.

> If you are referring to something else, can you elaborate? In 
> particular, if there is an RDFS entailment by an rdfs-consistent 
> graph which is not reducible to simple entailment by the rules given, 
> please let me know of it ASAP. Thanks.
> 
> Pat
> 
> >As of the last version of the
> >RDF Semantics document that I reviewed there was no operational
> >specification for RDFS entailment.
> >
> >Peter F. Patel-Schneider

peter
Received on Wednesday, 8 October 2003 10:41:03 EDT

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