- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Fri, 11 Jun 2004 08:31:27 -0400
- 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>
Eric- 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... -JH 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. > >[1] >http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/thread.html#247 >-- >-eric > >office: +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA >cell: +1.857.222.5741 > >(eric@w3.org) >Feel free to forward this message to any list for any purpose other than >email address distribution. -- 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