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Re: more sorting test cases

From: Jeen Broekstra <jeen@aduna.biz>
Date: Tue, 03 May 2005 10:42:42 +0200
Message-ID: <42773982.2090101@aduna.biz>
To: andy.seaborne@hp.com
Cc: public-rdf-dawg@w3.org

Seaborne, Andy wrote:

>> AFAICT this about covers most specified cases. I've come up with a 
>> number of other test cases as well (mixed bindings of untyped and 
>> typed literals, bnodes, etc.), but for most of these the spec does not 
>> specify a specific ordering.
> 
> 
> Ordering between mixed items is determined but ordering within them may 
> not be.
> 
> """
> (Lowest) no value assigned to the variable in this solution.
> Blank nodes
> URIs
> RDF literals
> """

Exactly, so it is useless to formulate test cases for these situations 
as each processor will do it differently anyway. Note that there _are_ 
test cases for mixed items, but only for those cases where the order 
is still clearly defined by the spec.

Basically the tests are limited to cases where the order is not 
processor-dependent.

> A total ordering isn't appropriate as Pat pointed out - it depends on 
> what datatypes the processor understands.

Even if a processor understood every imaginable datatype a total 
ordering is still inappropriate or even impossible. Some datatypes are 
simply not comparable at all. Heck, some datatypes are _themselves_ 
not (totally) ordered (xsd:dateTime and xsd:duration for example).

Related to that, I think the spec is not completely clear on one 
notion that we might want to be a bit more precise on. Suppose we have 
two datatyped literals of incomparable types, for example one is a 
xsd:float and the other a xsd:boolean. The spec says that for such 
cases order is undefined. Fine. Now suppose we have _two_ floats and a 
boolean:

"1E2"^^xsd:float
"1E4"^^xsd:float
"true"^^xsd:boolean

The spec only says that for incomparable types the result order is not 
defined. So strictly speaking, the spec not only endorses the above 
sorting, but also this:

"1E2"^^xsd:float
"true"^^xsd:boolean
"1E4"^^xsd:float

This is a rather weird and unnatural way of implementing sorting of 
course, but strictly speaking legal I think. Do we want to reword to 
prevent this?

Jeen
-- 
Jeen Broekstra          Aduna BV
Knowledge Engineer      Julianaplein 14b, 3817 CS Amersfoort
http://aduna.biz        The Netherlands
tel. +31 33 46599877
Received on Tuesday, 3 May 2005 08:40:42 GMT

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