W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > April to June 2009

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

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Wed, 27 May 2009 09:52:33 +0000
To: Simon Schenk <sschenk@uni-koblenz.de>, Paul Gearon <gearon@ieee.org>
CC: "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3646C2E0B49@GVW1118EXC.americas.hpqcorp.net>


> -----Original Message-----
> From: Simon Schenk [mailto:sschenk@uni-koblenz.de]
> Sent: 27 May 2009 06:59
> To: Paul Gearon
> Cc: Seaborne, Andy; Ivan Mikhailov; Axel Polleres; public-rdf-
> dawg@w3.org
> Subject: Re: [ACTION-18] use case on !ASK in FILTERS to emulate negation
> 
> Am Dienstag, den 26.05.2009, 12:41 -0500 schrieb Paul Gearon:
> > On Mon, May 25, 2009 at 12:48 PM, Seaborne, Andy
> <andy.seaborne@hp.com> wrote:
> > <snip/>
> > > 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#Disti

> nguish_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)?
> 
> I think there are two MINUS' out there: The Mulgara one basically is
> UNSAID, if I understand correctly. The SeRQL (and also RQL, I think) one
> has a set based semantics. Hence, you really need the same binding set,
> including the name, which makes it a bit complicated to use.

Agreed - and also SQL's MINUS is the set based one.  (ditto INTERSECTION)

[SQL Statement 1]
MINUS
[SQL Statement 2]

	Andy

> 
> Cheers,
> Simon
> --
> Simon Schenk | ISWeb | Uni Koblenz
> http://isweb.uni-koblenz.de

> http://www.uni-koblenz.de/~sschenk


Received on Wednesday, 27 May 2009 09:53:54 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:39 GMT