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Re: [ACTION-18] use case on !ASK in FILTERS to emulate negation

From: Paul Gearon <gearon@ieee.org>
Date: Tue, 26 May 2009 12:41:54 -0500
Message-ID: <a25ac1f0905261041j6371d890s39d09c3c49aac1c9@mail.gmail.com>
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: Ivan Mikhailov <imikhailov@openlinksw.com>, Axel Polleres <axel.polleres@deri.org>, "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
On Mon, May 25, 2009 at 12:48 PM, Seaborne, Andy <andy.seaborne@hp.com> wrote:
> Simon/Eric - you gave do you have examples where either MINUS or EXISTS can not easily be used where EXISTS or MINUS can?
> The distinguishing example is helpful - seem to me that MINUS needs a slightly artificial form to introduce ?name to be set-compatible with the preceding pattern.  But is this an artefact of the example and is there a counter example of EXISTs having to be slightly artificial?
> http://www.w3.org/2009/sparql/wiki/index.php?title=Design:Negation#Distinguish_MINUS_from_UNSAID

I don't see why you think {?x foaf:name ?name} is needed on the
right-hand-side of the MINUS to make it compatible. This term
restricts the set down to only those things that are named, but since
the query only takes it away from named things anyway, then the result
can't be any different. Including this term does make the MINUS
operate on less data, but at the expense of performing an extra join.

Or is the definition of MINUS here different to the one I'm used to
(the one implemented in Mulgara)?

Paul Gearon
Received on Tuesday, 26 May 2009 17:42:29 UTC

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