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Re: another aggregates test case...

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Tue, 08 Jun 2010 10:12:04 -0400
Message-ID: <4C0E4FB4.6080601@thefigtrees.net>
To: Andy Seaborne <andy.seaborne@talis.com>
CC: Axel Polleres <axel.polleres@deri.org>, SPARQL Working Group <public-rdf-dawg@w3.org>
On 6/8/2010 10:04 AM, Andy Seaborne wrote:
> I don't see why it needs to be an error - with no aggregation GROUP BY
> can be considered to be a a partial sort. Cardinality same as without
> GROUP BY. This also happens to be a requirement in some apps - results
> clustered by key but the same number of rows as without grouping.
> Sorting can make it so, but sorting is potentially more expensive.

This sounds like a pretty different model of aggregation then we have 
now. (Actually sounds similar to the model that was proposed on the 
comments list a few months ago.) If we went this way, why not do this 
all the time, and just repeat the values for the aggregate calculations?

I prefer to keep the existing aggregate model.


> Andy
> On 08/06/2010 2:20 PM, Lee Feigenbaum wrote:
>> I would expect this query to be an error, yes.
>> I'd also be happy to define an aggregate query as any query in which:
>> 1. A GROUP BY clause is present, OR
>> 2. An aggregate is included in the query projection
>> Lee
>> On 6/8/2010 9:07 AM, 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.
>>> Axel
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Received on Tuesday, 8 June 2010 14:41:49 UTC

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