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Re: Tests: data-r2/algebra

From: Jeen Broekstra <j.broekstra@tue.nl>
Date: Thu, 14 Jun 2007 10:59:28 +0200
Message-ID: <46710370.1030002@tue.nl>
To: andy.seaborne@hp.com
CC: RDF Data Access Working Group <public-rdf-dawg@w3.org>

Seaborne, Andy wrote:

> Checked in:
> 
> http://www.w3.org/2001/sw/DataAccess/tests/data-r2/algebra/
> 
> 12 tests.
> 
> These tests cover various issues to do with the SPARQL algebra, such as
> filter scopes, nested optionals, repeated optionals using the same
> variable.
> 
> There may well be duplication with tests elsewhere but it's probably
> useful to have a set focused on algebra matters all in one place.
> 
> This is not intended to be a complete coverage. If there are specific
> other areas for the algebra that people would like covered, please say
> so.  Or supply additional tests!

I'm having difficulties with the first test, Nested Optionals 1. Perhaps
I'm out of touch with how the behaviour of nested optionals is defined, but:

data:

:x1 :p 1 .
:x2 :p 2 .
:x3 :q 3 .
:x3 :q 4 .

query:

SELECT *
{
    :x1 :p ?v .
    OPTIONAL
    {
      :x3 :q ?w .
      OPTIONAL { :x2 :p ?v }
    }
}

I would intuitively expect the result to be:

 ?v ?w
  1  3
  1  4

According to this test, however, the result is:

 ?v ?w
  1  -

I guess this has something to do with the pattern in the second optional
not matching due to ?v being bound to value 1. However, given that this
is an optional pattern I do not quite understand why it makes the
_first_ optional clause fail as well.


Jeen
-- 
Dr. Jeen Broekstra                                          Den Dolech 2
Information Systems Group                                        HG 7.76
Department of Mathematics and Computer Science              P.O. Box 513
Technische Universiteit Eindhoven                      5600 MB Eindhoven
tel. +31 (0)40 247 36 86                                 The Netherlands
Received on Thursday, 14 June 2007 09:02:59 GMT

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