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Re: Proposal to drop disjunction requirement

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Fri, 1 Oct 2004 19:21:40 +0100
To: DAWG public list <public-rdf-dawg@w3.org>
Message-ID: <20041001182140.GC28819@login.ecs.soton.ac.uk>

On Fri, Oct 01, 2004 at 01:22:24 -0400, Kendall Clark wrote:
> On Fri, Oct 01, 2004 at 06:17:16PM +0100, Steve Harris wrote:
> > conjunctive ones, but it explodes the number of queries needed
> > dramatically.
> In cases where the implementation strategy is based on RDBMS/SQL or in
> every case? I genuinely don't know.

In every case - the algorithm prduces a number of prurely conjunctive
expressions from a mixed dis/con-juntive one. There may well be simple
omptisation strategys that mean you dont have to do the full naive
expansion, but I have no idea.
> > In any case, I'm not convinced that users generally think in terms of
> > graph level disjunction, as I said I've not had requests for it. 
> IIRC, Network Inference gets this a lot from its users and that's how
> 2.13 ended up in UC&R.
> > SQL has
> > no equivalent syntaxic form to graph disjunction
> Hmm, well, that's of only limited applicability here, IMO. But YYMV
> and clearly does. :>

:) I agree its a weak point, I just threw it in to show that theres
precident for not supporting disjuntive graph expressions.
> > > We have 2.13 and 3.13 in UC&R that imply disjunction in SPARQL. I
> > > haven't heard enough to disregard that.
> > 
> > 2.13 can be answered just as well with []'s, and 2.13 is the justification
> > for 3.13.
> Well, as you say, we don't have a proof that optionals can satisfy
> 2.13 in every case. We do have evidence that doing so in common cases
> puts a pretty high burden on users. Some of those
> disjunction-via-optional examples are a bit hairy. I can't imagine
> ordinary folks writing them.

Bear in mind that those are the /exact/ translations, the optional
expression users really write are the natural ones and dont have the hairy
disjuntive value constraints.
> Anyway, I've said my piece about this. Thanks for the response.

Thank you for raising the points. I certainly agree with you that none of
the points on thier own are reason enough to drop disjunction, but
together I think they make a good argument.

- Steve
Received on Friday, 1 October 2004 18:21:47 UTC

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