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Re: Order of evaluation for aggregates

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 15 Nov 2011 17:12:16 +0000
Message-ID: <4EC29D70.5010703@epimorphics.com>
To: Steve Harris <steve.harris@garlik.com>
CC: birte.glimm@uni-ulm.de, SPARQL Working Group <public-rdf-dawg@w3.org>

On 15/11/11 12:44, Steve Harris wrote:
> Many thanks Birte.
> OK, of these I suspect that changing the substitution to (SAMPLE(?x) AS ?x) will mean the least changes.

As syntax, (SAMPLE(?x) AS ?x) isn't legal because AS has to introduce a 
new variable. This happens in SELECT expression processing a few 

There is no definition of "Aggregation".  It's mentioned in 11.2 but the 
link goes to "Definition: Evaluation of Aggregation".  There should a 
definition (just after group?) in 18.4.

I looked because I wondered if we could just have an "?x" as the 
"aggregate".  But I think, as Birte shows, as because it's done by 
syntactic rewriting, just leaving it as "?x" would work.

> I wanted to convert the plain ?x projection to an aggregate so it was consistent with the rest of the projections, but expressing it explicitly would be equivalent I think.
> I will have a run through the aggregation text and see if I can make that change with a relatively small change to the document.
> Cheers,
>     Steve

I also noticed;

Definition: Evaluation of AggregateJoin
Note that if eval(D(G), Ai) is an error, it is ignored.

  An error causes an error doesn't it?  (AS causes it to be unbound)

Received on Tuesday, 15 November 2011 17:12:49 UTC

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