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Re: Final text for Basic Graph Patterns

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Thu, 19 Jan 2006 09:10:58 -0500
Message-Id: <3b1ade83329dafca9d1e2014cc698155@isr.umd.edu>
Cc: Dan Connolly <connolly@w3.org>, Pat Hayes <phayes@ihmc.us>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Enrico Franconi <franconi@inf.unibz.it>

On Jan 19, 2006, at 1:55 AM, Enrico Franconi wrote:

> On 19 Jan 2006, at 06:50, Bijan Parsia wrote:
>> It is also true that the current state of the deployed art, suitable 
>> for standardization, is conjunctive abox query alone. There there is 
>> a wealth of theory (see ian's and sergio's and enrico's (and others') 
>> papers), several reasonably optimized implementations (Racer, Pellet, 
>> KAON2, with Racer and KAON2 being commercial...I guess Cerebra also 
>> does conjunctive abox query, and it is, of course, commercial, but 
>> I'm not very familiar for it).  Oh, various subsets of OWL DL (e.g., 
>> DL Lite) also fit this model. It would be nice to standards this 
>> level so that we can get interoperability between the 4 query 
>> implementation. (I imagine FaCT++ will have something soon).
> Indeed. Ah, by the way, I wonder who *really* implements *correctly* 
> conjunctive queries with SHIQ (not fact, nor kaon2, nor racer, nor 
> cerebra; pellet?).

I'm hesitant, but I'll say, "yes, Pellet" (pace bugs). We implement the 
rolling up technique using nominals (since we have them). So, I feel 
pretty confident for tree like queries. For cyclic, we break up the 
query and roll up the pieces.

If there's some general flaw in these strategies, I'd love to know it.

Does KAON2 not hand nondistinguished variables correctly? We do have a 
bug in the current front end where presence in the select clause marks 
the variable as distinguished (and absence as non-distinguished).

(To see this compare:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX ns:  <http://www.mindswap.org/ontologies/oedipus#>

FROM <http://www.mindswap.org/ontologies/oedipus>
WHERE { ?x ns:hasChild ?y .
         ?y rdf:type ns:Patricide .
         ?y ns:hasChild ?z .
         ?z rdf:type ns:NotPatricide }

and the same query where ?Y is in the select clause. Frankly, what I 
*like* about this error is that it's easy to explore 
(non)distinguishedness without having to go through the GP replacing 
variables right and left. Oh well.)

Received on Thursday, 19 January 2006 14:11:10 UTC

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