- From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
- Date: Mon, 1 Nov 2010 16:12:58 +0000
- To: SPARQL Working Group <public-rdf-dawg@w3.org>
Hi all,
I was just wondering whether I can have something like double
negation/not exists within not exists, e.g., is
SELECT ?X WHERE { { ?x a ex:A } FILTER NOT EXISTS { FILTER NOT
EXISTS { ?x a ex:B } } }
a legal query? According to the grammar it seems to be, but from
looking at the algebra, I can't see how I would translate that into a
proper query algebra expression. There is still @@NOT EXISTS, so maybe
all will be clear once that is defined, but inuitively, I would expect
that when evaluating the innermost FILTER NOT EXISTS, I substract
solutions from the ?x a ex:A evaluation according to the filer, but
then it is unclear what the outer FILTER NOT EXISTS works on.
E.g., my default graph has:
ex:a1 a ex:A .
ex:a2 a ex:A .
ex:a2 a ex:B .
For the BGP ?x a ex:A, I get mu1=(x/ex:a1) and mu2=(x/ex:a2). When I
then evaluate FILTER NOT EXISTS { ?x a ex:B }, it remains
mu1=(x/ex:a1), but then?
Maybe I am overlooking something here or maybe the query is not legal?
Birte
--
Dr. Birte Glimm, Room 309
Computing Laboratory
Parks Road
Oxford
OX1 3QD
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+44 (0)1865 283520
Received on Monday, 1 November 2010 16:13:26 UTC