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Re: Objective 4.6 -- additional semantic information

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 11 Jun 2004 08:31:27 -0400
Message-Id: <p0611041ebcef55adcf17@[]>
To: "Eric Prud'hommeaux" <eric@w3.org>, Kendall Clark <kendall@monkeyfist.com>
Cc: Rob Shearer <Rob.Shearer@networkinference.com>, RDF Data Access Working Group <public-rdf-dawg@w3.org>

  I'm not against disjunction, but let me point out that the Algae 
case points out exactly the problem with disjunction -- if I have 
multiple disjunctive clauses then the cross product of all of them 
must be looked at somewhere -- in your case, you only had to do one 
query, but over on the server side your query engine had to run all 
four -- generally the problem w/disjunction is one of the many in 
query language design where you can either have easy query processing 
but the querier may have to do extra work or a more expressive query 
language that allows more powerful queries that are harder to process 
-- one way or the other the piper has to be paid...
p.s. FWIW, if I had to commit this minute, I'd propose we use a 
prolog like notion of allowing disjunction in the "where" clause -- 
it's a compromise between the two above, so that objective 4.6 seems 
to make good sense to me

At 16:53 +0900 6/11/04, Eric Prud'hommeaux wrote:
>On Wed, Jun 09, 2004 at 09:08:35PM -0400, Kendall Clark wrote:
>>  On Wed, Jun 09, 2004 at 04:59:18PM -0700, Rob Shearer wrote:
>>  > I must admit that upon re-reading the UC&R doc I am a bit surprised that
>>  > disjunction has fallen off the radar. I certainly think users like being
>>  > able to form arbitrary boolean constructions.
>>  FWIW, I was just thinking this today! Along the lines, "don't we need
>>  disjunction as an explicit requirement?" I don't know how or why
>>  disjunction use cases fell out of the doc; maybe this is one of those
>>  many mistakes I've made, but if so, it was totally unwitting.
>>  In other words, I think that disjunction should be an explicit
>>  requirement about disjunction, and I would be happy to help someone
>>  craft a use case that motivates it.
>>  > actually getting the benefit of the new system. If features like
>>  > disjunction are so rarely useful, then I fear a lot of us have wasted a
>>  > lot of time defining whole new languages like OWL and SWRL for
>>  > expressing things that are even more esoteric!
>>  I don't think that's the case at all -- rather, I think that
>>  disjunction just fell off the map. Let's get it back on.
>[1] finds an Annotea use case motivated by eliminating 3 extra queries
>(in fact, why I put disjunction into Algae). I provided Algae syntax
>and Alberto provided RDQL syntax.
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Professor James Hendler			  http://www.cs.umd.edu/users/hendler
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-277-3388 (Cell)
Received on Friday, 11 June 2004 08:39:56 UTC

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