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/~sschenk
Received on Wednesday, 27 May 2009 08:49:39 UTC