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From: Paul Gearon <gearon@ieee.org>
Date: Mon, 29 Jun 2009 13:02:57 -0500
Message-ID: <a25ac1f0906291102p403e57e0qda7f8745e8343c17@mail.gmail.com>
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
On Mon, Jun 29, 2009 at 9:21 AM, Seaborne, Andy<andy.seaborne@hp.com> wrote:
>> -----Original Message-----
>> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-
>> request@w3.org] On Behalf Of Simon Schenk
>> Sent: 29 June 2009 10:36
>> To: public-rdf-dawg@w3.org
>> Subject: UNSAID vs MINUS
>> ACTION-32  http://www.w3.org/2009/sparql/track/actions/32
>> To revive the discussion on negation, I would like to point you to the
>> overview of options for implementation at:
>> http://www.w3.org/2009/sparql/wiki/Design:Negation
>> In particular, binary operators vs. FILTER expressions, and set based
>> MINUS in SeRQL vs UNSAID are discussed. Note that MINUS in SeRQL !=
>> MINUS in Mulgara (?), which has the same semantics as UNSAID.
>> Cheers,
>> Simon
> Good time to revive it.
> (I reorganised the page end of Friday - didn't remove any text intentionally but I put the two
> options in separate sections.  I generally called it NOT EXISTS.)
> To make progress on this, let's take it in two steps.
> 1/ Decide on UNSAID vs Set-MINUS, that is resolve to explore one design in depth
> 2/ Then take as a sub-issue of NOT EXISTS as to have a graph operator and/or a FILTER
> expression.
> I propose we adopt the UNSAID/NOT EXISTS design.  The Set-MINUS seems to have no
> advantages because it is equivalent to an NOT EXISTS form, but requires each side to be a
> set, which would need to be worked through the rest of the language.

I agree with this proposal. The UNSAID approach makes it very easy to
express a lot of concepts, but Set-MINUS can be very hard to structure
some queries. Given that Set-MINUS is a degenerate form of UNSAID then
I think this strengthens the argument for UNSAID.

> On the second part, I found it to be no more work as the graph operator is the introduction of
>  algebra-level filter.

It was a straighforward implementation in Mulgara. It took longer to
attempt the algebraic description than it took to write the code.

Paul Gearon
Received on Monday, 29 June 2009 18:03:44 UTC

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