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Re: another aggregates test case...

From: Axel Polleres <axel.polleres@deri.org>
Date: Tue, 8 Jun 2010 16:14:58 +0100
Cc: "Steve Harris" <steve.harris@garlik.com>, "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-Id: <B82FFE1D-7426-4513-B774-9063D4F8CCB8@deri.org>
To: Lee Feigenbaum <lee@thefigtrees.net>
> I think that Axel means that:
> 
> SELECT ?v1 ?v2 ?v3
> WHERE
> { ... }
> GROUP BY ?v1 ?v2 ?v3
> 
> is equivalent to:
> 
> SELECT DISTINCT ?v1 ?v2 ?v3
> WHERE
> { ... }
> 

yes, that's what I meant.

> ...and I think he's right in that observation?

I hope I am  :-)

Axel

On 8 Jun 2010, at 14:42, Lee Feigenbaum wrote:

> On 6/8/2010 9:14 AM, Steve Harris wrote:
> > On 2010-06-08, at 14:07, Axel Polleres wrote:
> >
> >> Student of mine pointed me to a somewhat corner test case:
> >>
> >> PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>
> >> PREFIX rdfs:<http://www.w3.org/2000/01/rdf-schema#>
> >> PREFIX dcterms:<http://purl.org/dc/terms/>
> >> PREFIX foaf:<http://xmlns.com/foaf/0.1/>
> >> PREFIX mpp:<http://imp.deri.ie/ontology/moviePostProcessing#>
> >>
> >> SELECT *
> >> FROM NAMED<http://imp.deri.ie/vff/ppa/projects>
> >> FROM NAMED<http://imp.deri.ie/vff/ppa/people>
> >> WHERE {
> >>
> >> ?project rdf:type foaf:Project ;
> >>           rdfs:label ?title .
> >> ?person rdf:type mpp:Person ;
> >>           rdfs:label ?personName ;
> >>           foaf:currentProject ?project .
> >> }
> >> GROUP BY ?project
> >>
> >> Actually, I *think* this should be syntactically invalid, as per:
> >> "In aggregate queries and sub-queries only expressions which have been used as GROUP BY expressions, or aggregated expressions (i.e. expressions where all variables appear inside an aggregate) can be projected."
> >>
> >> interestingly, the formulation - strictly speaking - doesn't say what an aggregate query is, but GROUP BY without aggregtate doesn't make a lot of sense anyways, except that it should have the same effect as DISTINCT, right(?), but we still don't want to allow in the presence of GROUP BY some non-grouped/aggregated things to be projected, I assume.
> >
> > It wouldn't have the same affect as DISTINCT as per the current draft. Cardinality is preserved.
> 
> I think that Axel means that:
> 
> SELECT ?v1 ?v2 ?v3
> WHERE
> { ... }
> GROUP BY ?v1 ?v2 ?v3
> 
> is equivalent to:
> 
> SELECT DISTINCT ?v1 ?v2 ?v3
> WHERE
> { ... }
> 
> ...and I think he's right in that observation?
> 
> Lee
> 
Received on Tuesday, 8 June 2010 15:15:32 GMT

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