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RE: Semantics of aggregates

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Tue, 1 Sep 2009 17:08:47 +0000
To: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693CEC28F6@GVW1118EXC.americas.hpqcorp.net>
> > My idea of a common case is when all the rows grouped have the same
> > type or are undefined.  Is that your common case?
> No. Our apps have two cases, one where we control the data (or at
> least the conversion of it) and one where take in arbitrary data from
> outside. I imagine that some people have apps with some combination of
> these two, but currently we don't.

Could you make that a concrete example, with the answers that might make sense to you? (test case mode = on)

> In the first case it's as you say, either it's not present, or it's a
> known datatype, in the second case you get all kinds of values.

Let's get concrete:

Does option 5 [1] have initial consensus? Use the relationship as given by "ORDER BY" which includes "<".

This gives a spec-determined answer for many cases but not all.  Local implementations may give a total ordering using "ORDER BY" but it's not to be relied on across implementations (I could not do that in ARQ because the ordering changes as you add datatypes understood by "<")

With this:

SELECT MIN(?x) { .. } # No GROUP BY
 is the same as:
SELECT ?x { .. } ORDER BY ?x LIMIT 1

where ORDER BY is determined.

Across a mix of type of RDF node, you may not get the type your application wants but that is possible if you use MIN(some expression).

What cases do people see where this is inconvenient?


[1] LeeF: http://lists.w3.org/Archives/Public/public-rdf-dawg/2009AprJun/0247.html 


Received on Tuesday, 1 September 2009 17:10:56 UTC

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