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#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)? 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. Cheers, Simon -- Simon Schenk | ISWeb | Uni Koblenz http://isweb.uni-koblenz.de http://www.uni-koblenz.de/~sschenkReceived on Wednesday, 27 May 2009 08:49:39 UTC
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