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RE: [TF-ENT] RDFS entailment regime proposal

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Tue, 29 Sep 2009 09:52:50 +0000
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>, SPARQL Working Group <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693EA8D780@GVW1118EXC.americas.hpqcorp.net>


> -----Original Message-----
> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-
> request@w3.org] On Behalf Of Birte Glimm
> Sent: 28 September 2009 22:09
> To: SPARQL Working Group
> Subject: Re: [TF-ENT] RDFS entailment regime proposal
> 
> Andy,
> scalability is important, but it is not the only driving factor for
> me. I am still hesitant to have MAY instead of MUST because we then
> specify a system behavior that tolerates the violation of the RDFS
> entailment lemma from the RDF spec for the RDFS entailment regime. It
> can give better performance under an RDFS entailment regime, but
> interpreting blank nodes as normal names would also give you much
> better performance in many cases and nevertheless that is not what is
> and should be done.

I'm not proposing any change to bNode handling.
 
> I want to understand the consequences that such a change has and since
> it can violate the very basic underlying principles, such as the RDFS
> entailment lemma, I think one should be very careful with such a
> change.
> 
> Apart from scalability, a consistent behavior of SPARQL engines under
> an RDFS entailment regime is also important to me. What is not good
> from an interoperability point of view is that one system gives you
> answers A and another gives you answers B or in this case, one system
> answers the query and another says the data is inconsistent. Which
> system is correct? Both because the one that gave an answer just
> didn't see the inconsistency? If you query the same data twice with
> the same query, can it happen that for the first query you get an
> answer, then the system answers some other query maybe from another
> user, which makes it recognize the inconsistency, and then I ask my
> same query again and then I get an inconsistency message? I would find
> that not a nice behavior.
> 
> It is definitey something we should discuss in the telcon if we have
> the time and if not, I would like to have some more opinions on that
> and some more explanations of the effects that such a change would
> have.
> 
> Birte

There are implicit assumption on the processing model that would make it hard for a backward chaining engine to work with, say. (They would seem to have to a consistency check as well as answer the query).  I think it's an important to pull out these assumptions and state them - hence the requirements needs.

(I know there is there's no mention of OWL-RL in the document (although I haven't yet understood that matter)).

The OWL2 conformance spec [1] does not require an OWL2-RL query answering system be based on a consistency checker; even if it is, and the checker returns "unknown" (RDF-Based Semantics), as might be the case if the data is outside theorem PR1, what happens?  So I think we need to deal with similar situations anyway.

	Andy

[1] http://www.w3.org/TR/2009/PR-owl2-conformance-20090922/#Query_Answering_Tool


Received on Tuesday, 29 September 2009 09:54:31 GMT

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