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Re: Final text for Basic Graph Patterns

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Wed, 18 Jan 2006 11:55:58 +0100
Message-Id: <C435F239-F215-4A41-BDF6-62ACDF402EA7@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 18 Jan 2006, at 04:58, Pat Hayes wrote:

>> But, you probably did not pay attention to our text:
>> "In fact, with the proviso that bnodes are not allowed to appear  
>> in pattern solutions, SPARQL may be extended to provide a way to  
>> override the default "simple entailment" with "RDF entailment",  
>> "RDFS entailment" (as defined in [RDF-MT]), and "OWL  
>> entailment" (as defined in [OWL-Semantics], where the syntactic  
>> restrictions in OWL-DL or OWL-Lite should be reflected in suitable  
>> syntactic restrictions on the form of basic graph patterns)."
>>
>> So, we suggest an upward compatible extension *without* bnodes in  
>> the answer, because it is the only one which we know is going to  
>> work for sure (it is easy to see this). As our latest interactions  
>> proved, it is an open research problem how to have a query  
>> language with bnodes in the answer based on entailment which can  
>> also smoothly work with simple entailment.
>
> I am still bothered by the possibilities of OWL-specific notions of  
> redundancy in answer sets. Consider an OWL/RDF KB that asserts
>
> :a rdf:type :A
> :a rdf:type :B
> :a rdf:type :C
> :A rdf:type owl:Class
> :B rdf:type owl:Class
> :C rdf:type owl:Class
>
> and an OWL query
>
> SELECT ?x WHERE {:a rdf:type ?x .}

Look, this is not a legal OWL-DL query. We pointed out in our old  
proposed text (and also in the new one). We allow in OWL-DL only  
queries that carry similar syntactic restrictions as OWL-DL  
expressions. This boils down to allow only for non-high order RDF  
graphs as BGPs (defined in [1]). So the above query is not of our  
concern in OWL-DL.
As far as OWL-full is concerned, my very personal position is that I  
don't care, since I don't believe it makes *currently* any sense at  
all :-)
So, whatever you say about OWL-full, is fine for me...

> Now, this dataset OWL-entails the *existence* of a triple  
> intersection and three double intersections, all with :a in them.  
> So are these reasonable answer bindings for such a query? I see no  
> good reason why they should not be: in fact, one could reasonably  
> take the position that the *only* non-redundant answer here would  
> be to bind ?x to a term representing the most restrictive  
> intersection. But to construct such a term would require the use of  
> the RDF collection vocabulary when presenting the answer.

Even if we allow high-order queries like the above in OWL-DL, the  
scoping set B would be restricted to be URIs in OWL-DL, so the  
problem doesn't show up in OWL-DL anyway!
And, again, as far as OWL-full is concerned, see above :-)

> I'd be interested in your reaction to the suggestion for how to  
> define 'extensions'. I tried to keep the basic structure of the  
> definition, but remove just the parts that might need to be  
> reconsidered more carefully. But in the light of the above, perhaps  
> I was trying to be too ambitious.

I really like your idea of the scoping set B. See my other email.

cheers
--e.

[1] Jos de Bruijn, Enrico Franconi, Sergio Tessaris (2005). Logical  
Reconstruction of normative RDF. Proc. of the Workshosp on OWL  
Experiences and Directions (OWLED 2005), Galway, Ireland, November  
2005. <http://www.inf.unibz.it/~franconi/papers/owled-05.pdf>
Received on Wednesday, 18 January 2006 11:03:26 GMT

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