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

From: Simon Schenk <sschenk@uni-koblenz.de>
Date: Tue, 26 May 2009 12:10:51 +0200
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>
Message-Id: <1243332651.13942.27.camel@tweety>
Am Montag, den 25.05.2009, 17:48 +0000 schrieb Seaborne, Andy:

> 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 think there are cases, which can not be expressed using one of
the forms: EXISTS can be translated into MINUS by extending the pattern,
if necessary. However, MINUS really is a bit ugly in many cases.

> > In addition, I still think that EXISTS without FILTER around are a bit
> > confusing, esp. if the next clause is OPTIONAL {...}.
> 
> I'm tending to both forms although underneath raw EXISTs because I thing using iut on its own is going to be common.  Internally, it behaves just like a FILTER which is not moved to the end of a BGP.

I think FILTER better captures the intended semantics. I am not sure,
whether an order dependent inline form is intuitive. On the other hand,
aesthetically I like it better. :) Why not completely translate it into
a FILTER, including a reordering?

Cheers,
Simon

-- 
Simon Schenk | ISWeb | Uni Koblenz
http://isweb.uni-koblenz.de
http://www.uni-koblenz.de/~sschenk


Received on Tuesday, 26 May 2009 10:11:35 GMT

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