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

From: pat hayes <phayes@ihmc.us>
Date: Wed, 8 Oct 2003 09:35:34 -0500
Message-Id: <p06001f0fbba9ced77890@[10.0.100.25]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: w3c-rdfcore-wg@w3.org

>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? 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.

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


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Received on Wednesday, 8 October 2003 10:35:39 EDT

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