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Re: Final text for Basic Graph Patterns

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Thu, 19 Jan 2006 19:00:06 +0100
Message-Id: <8D7DF829-1B52-4A58-BF5B-88745382E240@inf.unibz.it>
Cc: Dan Connolly <connolly@w3.org>, Bijan Parsia <bparsia@isr.umd.edu>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Pat Hayes <phayes@ihmc.us>

On 19 Jan 2006, at 18:33, Pat Hayes wrote:
> Of course. You miss my point. I was simply following the general  
> pattern of how SPARQL queries are defined, using our most recent  
> attempt at an 'entailment-based' general form of definition, and  
> applying that to OWL-DL as described in the OWL spec, and seeing  
> what we finish up with. ( {:a rdf:type :b} is legal OWL-DL, under  
> appropriate constraints, and is an instance of the query under  
> binding of a variable to a legal OWL-DL identifier, so... ) I meant  
> only that if one takes a 'natural' extension of SPARQL to OWL,  
> keeping the basic form of the definitions but replacing simple  
> entailment by OWL-DL entailment, then examples like this turn up.

What I am also saying that you have to transport the syntactic  
constraints that OWL-DL expressions have, to similar syntactic  
constraints to SPARQL queries when using OWL-DL entailment. Namely,  
in queries bnodes and variables are not in property position of any  
triple, nor in object position of rdf:type triples, and there is no  
rdf, rdfs, owl vocabulary symbol in the query with the exception of  
rdf:type in property position.

> The only reason for our discussing this matter at all *in this  
> forum* is because some folk - notably, Bijan and yourself - have  
> argued forcibly that the SPARQL definitions should be couched in a  
> way which generalizes naturally to the OWL case, by replacing  
> 'simply entails' with 'OWL-DL entails' in the definitions. That is  
> what I did.

And in fact I have the same goal. But I also know the limits to put  
in order for the machine to work.

>> First of all, I have been sloppy in my statement, since OWL-DL  
>> queries do not exist - we are defining them now here. Now, there  
>> is *no* theoretical nor practical result that even considers  
>> queries of that kind in the DL literature.
>
> I do not dispute this. As I said, I was simply applying the  
> proposed SPARQL definitions to OWL-DL (as defined in the OWL  
> specs). If this gets us to an area that has not yet been explored  
> in the research literature, that seems to me to be in fact an  
> extremely good reason for NOT including ANY mention of OWL in the  
> SPARQL documents at all, other than perhaps an informative warning  
> that this is an open problem area unsuitable for standardization at  
> the present.

In my text, I am proposing to have an informative statement saying  
that a safe way to have a working SPARQL with OWL-DL entailment is to  
restrict the scoping set B to include only URIs, and to have the  
above syntactic restrictions to the SPARQL BGPs.

cheers
--e.
Received on Thursday, 19 January 2006 18:00:14 GMT

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