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Re: Proposed change to the OWL-2 Direct Semantics entailment regime

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Wed, 1 Dec 2010 08:02:35 +0100
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <0D19F959-8566-4FA1-9E07-82EA86231511@inf.unibz.it>
To: Lee Feigenbaum <lee@thefigtrees.net>

On 30 Nov 2010, at 16:31, Bijan Parsia wrote:

> On 30 Nov 2010, at 14:51, Lee Feigenbaum wrote:
> 
>> On 11/30/2010 9:49 AM, Enrico Franconi wrote:
>>> I repeat myself: *any* OWL-QL or OWL-EL implementation by design incorporates BGPs with OWL Direct Semantics in the manner I'm proposing.
> 
> This is pretty obviously false, afaict. But maybe you were being hyperbolic?

Well, I just said that the way any publication/manual defines the semantics of any tool supporting conjunctive queries with distinguished variables in the OWL-QL and OWL-EL families is exactly what I'm proposing. This is obviously true.

> Nothing prevents an engine with non-distinguished variables + existential variable interpretation of bNodes in data from leaving the query engine untouched and skolemizing the data on input.

I don't think so for the following reason. In any DB related technology (such as OWL-QL, or in recent works on OWL-EL) you have necessarily built in the unique name assumption. If your language has counting or functionalities (such as OWL-QL) then skolemising the bnodes as individuals would be plain wrong, as you can easily imagine.

> But no, I don't think the implementation cost is high.

As a consequence of the above, you need to implement specific ways to handle bnodes *in* the engine. I can't imagine how this could be simply done, since the technology is based on rewriting queries as SQL queries, but then your pseudo-skolems in the DB would have UNA, etc...

>> i.e. wouldn't we be asking all current SPARQL-OWL implementations to change their behavior?
> 
> The big one is returning bNodes, as Enrico pointed out. But the gain in SPARQL/RDF compatibility would be worth it, IMHO.

Same issue as above. If you language has built-in UNA, then the reimplementation is not going to be trivial IMHO.

--e.

> 
> Cheers,
> Bijan.
> 
Received on Wednesday, 1 December 2010 07:03:11 GMT

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