# Re: First order logic and SPARQL

From: Axel Polleres <axel.polleres@deri.org>
Date: Sun, 5 Sep 2010 16:29:14 +0100
Cc: "Bob MacGregor" <bob.macgregor@gmail.com>, "Juan Sequeda" <juanfederico@gmail.com>, "Jitao Yang" <jitao.yang@gmail.com>, <semantic-web@w3.org>, <public-sparql-dev@w3.org>
Message-Id: <723F0CAE-2DDC-4269-8537-A2C1DA957CA3@deri.org>
To: "Bijan Parsia" <bparsia@cs.man.ac.uk>
```
On 5 Sep 2010, at 16:26, Bijan Parsia wrote:

> 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.

Yup. The spec algebra is slighlty different from the simplified one in the
papers (multiset semantics, some small differences on FILTERs within OPTIONALs
and treatment of errors in FILTERs), but apart from that the papers lay the
foundations accurately, IMO.

Axel
>
> Cheers,
> Bijan.
>
```
Received on Sunday, 5 September 2010 15:29:49 UTC

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