- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Fri, 11 Jun 2004 22:10:07 +0900
- To: Jim Hendler <hendler@cs.umd.edu>
- Cc: Kendall Clark <kendall@monkeyfist.com>, Rob Shearer <Rob.Shearer@networkinference.com>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
On Fri, Jun 11, 2004 at 08:31:27AM -0400, Jim Hendler wrote: > > 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 I'm not sure I follow. The Algae server had to recurse down the left side of the disjunction, and, if it found nothing, down the right side (it's treated as a shortcut OR, not a union). I think this had roughly the overhead of introducing half of a new conjunction constraint. When translated to SQL, I think the server has a similar burden. I'm not dead-set for disjunction, but want to make sure we make the decisions for the right reasons. I think that Alberto said that it would be inefficient to impelement disjuntion in his (very slick) database. But I'm not sure we want to keep users from haing ineffic- ient tools at their disposal. > -- 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 Could you explain this a bit, either privately or on list? I don't know anything about this. (If it's a pain, feel free to tell me to read a book.) > 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) -- -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.
Received on Friday, 11 June 2004 09:09:58 UTC