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Re: grouping by expressions

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 03 Nov 2010 16:22:53 +0000
Message-ID: <4CD18C5D.4060501@epimorphics.com>
To: Steve Harris <steve.harris@garlik.com>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>


On 03/11/10 15:42, Steve Harris wrote:
>> ex:agg(?y, ?z)+1 is an expression - it needs a solution to calculate the "+".
> Yeah, makes sense in Projection, but that doesn't apply to grouping, does it? "Naming" expressions is compulsory in SELECT already, as they have to be associated with some variable name in the result format.
>

And before the projection step?

If we have

SELECT (ex:agg1(?y, ?z)+ex:agg2(?y, ?z)+1 AS ?A)
{
...
}
GROUP BY ?x

then in each row, each ex:agg?(?y, ?z) needs to turn into a value. 
Operator + evaluates each argument, then calls op:numeric-add.

How, in expression evaluation, does ex:agg1(?y, ?z) get mapped to a 
value?  I would like to avoid wholesale changes to expression evaluation 
unless there is no other way.

	Andy
Received on Wednesday, 3 November 2010 16:23:34 GMT

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