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Re: SPARQL semantics: open issues for basic query patterns

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 2 Jan 2006 13:28:46 -0600
Message-Id: <p06230909bfdf2d4779ef@[]>
To: Enrico Franconi <franconi@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>On 27 Dec 2005, at 19:37, Enrico Franconi wrote:
>>a) in the document only 'simple entailment' is used. We want a
>>parametric entailment, with simple, rdf, rdfs explicit at least, and
>>owl-dl and owl possible. The argument here is that due to the infinite
>>closure of RDF graphs (due to rdf:1, rdf:2, etc; or to the
>>reification), this document would not even allow to have
>>implementations that comply with the original RDF MT! Moreover, there
>>are explicit requests about this in the SWBP WG, for example
>Please note that there is a simple non invasive mode to satisfy this 
>requirement: just add at the beginning of the document a note saying 
>that whenever simple entailment is mentioned, we could actually use 
>also RDF, RDFS, OWL-DL entailemnts.

I don't think this makes sense. First, what about D-entailment, or 
other semantic extensions that have no official name? What about 
using just a few pieces of OWL, eg functionalProperty and sameAs, but 
without undertaking to check, say, cardinality restrictions? There is 
no name for this, but it is in use.

But in any case, if we say this, what exactly does the spec specify? 
Suppose we say this, and A implements a SPARQL server using, say, RDF 
entailment, while B implements one using OWL entailment, and C 
implements one using a semantic extension of RDF which has no name as 
yet. The same query, pointed to the same target graph, gets different 
answers from A, B and C. And yet they all satisfy the requirements of 
the spec, since the spec no longer says what kind of entailment 
should be used. If we allow any kind of semantic extension (a 
possibility which was deliberately put into the RDF spec) then almost 
any answer to a query is possible, and hence legally sanctioned by 
the SPARQL spec. Surely the whole point of SPARQL is to avoid this 
kind of a situation.



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Received on Monday, 2 January 2006 19:28:53 UTC

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