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Re: Comments on aggregation in SPARQL 1.1

From: Graham Klyne <graham.klyne@zoo.ox.ac.uk>
Date: Wed, 18 May 2011 08:19:46 +0100
Message-ID: <4DD37312.3080907@zoo.ox.ac.uk>
To: Steve Harris <steve.harris@garlik.com>
CC: public-rdf-dawg-comments@w3.org
For the purposes of your formal process, please treat this as acknowledgement of 
satisfactory resolution.


Issue 2 is certainly resolved.

For issue 1, I think the test cases probably help out, but they're not so easy 
to navigate for casual enquiry.  Is there a human-readable version of the test 
case manifest?  It seems much of the data is there from which one could be 
generated automatically.


Steve Harris wrote:
> In response to http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2010Sep/0000.html
>  > 1. Editorial
>  >
>  > I'm finding the section on aggregates is quite hard to follow.
>  >
>  > More examples, especially for GROUP_CONCAT, might make it easier
>  > to understand the link between the algebra and its practical consequences
>  > in SPARQL queries.
> There is a balance between providing examples, and making the document too long.
> The explanatory section on aggregates has been expanded, and there are now some testcases for aggregates http://www.w3.org/2009/sparql/docs/tests/data-sparql11/aggregates/ - which hopefully illustrate the behaviour.
>  > Also, I can't find any indication of the interaction between GROUP BY and ORDER
>  > BY, where the ORDER BY specifies a variable not named in the GROUP BY: is this
>  > allowed? If so, what effect does it have (e.g. on GROUP_CONCAT)?
> Aggregate operations are performed on a multiset, so order is not preserved.
> The group discussed the possibility of adding this feature but decided to postpone it to a future working group.
> Please note: “ORDER BY after a GROUP BY must only use variables exposed by the GROUP.  Use of non-grouping variable outside the GROUP BY is not legal and a required syntax error.”
> For example:
>    SELECT ?book ?title
>    WHERE {
>      ?book dc:title ?title }
>    GROUP BY ?book
>    ORDER BY ?title
>    ==> error.
>  > 2. A Nice-to-have feature
> We understand that you have now seen another solution to this issue, see http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2010Oct/0001.html.
> Could you please respond to this message saying whether this comment has been answered to your satisfaction.
> Regards,
>    Steve, on behalf of the SPARQL Working Group
Received on Wednesday, 18 May 2011 10:59:27 UTC

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