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RE: DISTINCT()

From: Polleres, Axel <axel.polleres@siemens.com>
Date: Wed, 14 Mar 2012 11:45:22 +0100
To: Andy Seaborne <andy.seaborne@epimorphics.com>, "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
Message-ID: <9DA51FFE5E84464082D7A089342DEEE80137B3693FA2@ATVIES9917WMSX.ww300.siemens.net>
(sorry, hot "send" to early)

> Could you expand on "we need DISTINCT"?  Is that just a technical 
> point that DISTINCT covers more or a political point about the 
> comments?

For me this is definitly a technical point, since a DISTINCT-paths
-semantics, which can be optimized/efficiently implemented, doesn't 
seem to be feasible by recognizing DISTINCT subqueries alone, 
at least not trivially...

I.e., while DISTINCT() can possibly be defined in terms of a rewriting 
(which introduces fresh variables for blank nodes), I think that's neither 
elegant nor very practical for optimizations without the explicit keyword, 
whereas a syntactic element DISTINCT() gives a direct handle for 
optimizations, right? 

So, I think this is important *both* technically and in in order 
to address the comments.

> What about the lesser case of just {*}{+} and *+ changes?

I am fine with having those, but for the reasons above, I would 
feel uncomfortable going without DISTINCT().

Best,
Axel 

 
--
Dr. Axel Polleres
Siemens AG Österreich
Corporate Technology Central Eastern Europe Research & 
Technologies CT T CEE 
 
Tel.: +43 (0) 51707-36983
Mobile: +43 (0) 664 88550859
Fax: +43 (0) 51707-56682 mailto:axel.polleres@siemens.com 
 

> > -----Original Message-----
> > From: Andy Seaborne [mailto:andy.seaborne@epimorphics.com] 
> > Sent: 14 March 2012 11:02
> > To: public-rdf-dawg@w3.org
> > Subject: Re: DISTINCT()
> > 
> > On 14/03/12 09:48, Polleres, Axel wrote:
> > > Just my two cents to emphasize that I tend to agree on 
> > that: I believe 
> > > we need DISTINCT() to address JC-4 and related comments in 
> > a fashion 
> > > agreeable to the commenters.
> > 
> > Could you expand on "we need DISTINCT"?  Is that just a 
> > technical point that DISTINCT covers more or a political 
> > point about the comments?
> > 
> > What about the lesser case of just {*}{+} and *+ changes?
> > 
> > 	Andy
> > 
> > 
Received on Wednesday, 14 March 2012 10:45:50 GMT

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