On 5 Sep 2010, at 16:17, Axel Polleres wrote:
The problem with SPARQL stems from the OPTIONAL operator. A mantra
of RDF has been that it
has open world semantics. The OPTIONAL operator is inherently non-
monotonic.
?? I don't think so. I'd be interested in a reference.
Obviously OPTIONAL is nonmomotonic and in fact, NOT EXISTS can be
emulated not only
with the widely known OPTIONAL + FILTER !Bound() trick (see [1]
Query #13 for an example),
but you actually don't need the FILTER even (see Query #14 in the
same tutorial [1]).
[snip]
Thanks, brain fart on my part. (It was a chain from relational algebra/
calculus correspondence. Oh well :))
However, I think the point that SPARQL/1.0 is well defined in terms of
the relational algebra holds. Your work validates that.
Cheers,
Bijan.
