- 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>
> -----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 UTC