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

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Tue, 30 Nov 2010 15:52:28 +0100
Cc: Bijan Parsia <bparsia@cs.man.ac.uk>, SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <020E99C9-6BE9-47F9-89AC-4C844B5D8D53@inf.unibz.it>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>

On 30 Nov 2010, at 15:17, Birte Glimm wrote:

> I am actually with Bijan here and I don't think my position is
> captured well in your statement "I already had an informal chat about
> this with Birte, Axel, and Ivan, and they seem to be in favour if the
> majority agrees." I prefer it the way it is, but if there is a
> majority who thinks it shouldn't be that way, I won't object.
> 
> I can see some of your points, but a) you can always rewrite your
> queries to use complex OWL concepts with existential if you want to
> capture the semantics

I am not aware of such a result, and if this could ever happen it would be an exponential rewriting due to complexity reasons.

> and b) I agree with Bijan's point here that
> although I did my PhD on queries with non-distinguished variables, I
> could never find any convincing real example where you would need the
> real existential meaning and I never managed to find a user who needed
> that even if they uderstood the intricacies of non-distinguished
> variables.

My example isn't good enough? If RDF would be able to express covering, my example could be written in this RDF+.
Most importantly, *the* qualifying aspects of the two most important OWL profiles (OWL2-QL and OWL2-EL) are exactly the presence of proper conjunctive queries. These two large communities (involved in DB applications the first, and in medical applications the latter) will NOT use SPARQL if SPARQL will not include non-distinguished variables

> Speaking as HermiT implementor, Ian, Boris, and I prefer the current
> regime and it would be even better if even RDF makes an official move
> to treating bnodes as constans that don't have a particular name,
> rather than as existential variables.

This is irrelevant here. The point I'm making is to have queries with non-distinguished variables. Full stop.

--e.
Received on Tuesday, 30 November 2010 14:53:02 GMT

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