- From: Steve Harris <steve.harris@garlik.com>
- Date: Tue, 17 May 2011 16:22:21 +0100
- To: public-rdf-dawg-comments@w3.org
- Cc: graham.klyne@zoo.ox.ac.uk
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 -- Steve Harris, CTO, Garlik Limited 1-3 Halford Road, Richmond, TW10 6AW, UK +44 20 8439 8203 http://www.garlik.com/ Registered in England and Wales 535 7233 VAT # 849 0517 11 Registered office: Thames House, Portsmouth Road, Esher, Surrey, KT10 9AD
Received on Tuesday, 17 May 2011 15:22:50 UTC