- From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
- Date: Wed, 4 Aug 2004 19:18:32 +0100
- To: public-rdf-dawg@w3.org
On Wed, Aug 04, 2004 at 09:54:10 -0700, Bob MacGregor wrote: > BRQL should be commended in adding the OPTIONAL > clause. However, I see two problems. First is that it doesn't > support nested optional matches (their document acknowledges > this issue). Second, BRQL makes a distinction between > WHERE and AND restrictions. Both of these should be > allowable in the OPTIONAL clause, but they aren't (as far > as I can tell). I disagree with this for a number of reasons, first, I think AND is helpful for readability and familarity to SQL users, and I dont think that optional AND makes sense in many examples, eg: a) SELECT ?x WHERE (<foo>, <bar>, ?x) OPTIONAL (?x, <math:greater-than>, 120.0) is equivalent to b) SELECT ?x WHERE (<foo>, <bar>, ?x) as far as I can see. c) SELECT ?x, ?y WHERE (<foo>, <bar>, ?x) OPTIONAL (?x, <math:greater-than>, ?y) is different to b), but I'm not sure what it would be useful for in real-world examples, and it would infact be quite dangerous to allow queries of this sort. - Steve
Received on Wednesday, 4 August 2004 14:18:38 UTC