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Re: REDUCED and the SPARQL XML Results Format

From: Lee Feigenbaum <feigenbl@us.ibm.com>
Date: Wed, 28 Mar 2007 02:52:07 -0400
To: andy.seaborne@hp.com
Cc: dawg mailing list <public-rdf-dawg@w3.org>
Message-ID: <OFE9591CE0.38E3126A-ON852572AC.002558E9-852572AC.0025BAFF@us.ibm.com>

Andy Seaborne wrote on 03/26/2007 07:25:16 AM:
> Steve Harris wrote:
> ...
> > Whether the distinct attribute should be set where appropriate is an 
> > interesting question. It also applies to SPARQL services that 
> > currently implicitly DISTINCT.
> 
> I don't see much use for a distinct attribute (I do see more utility for 
the 
> 'ordered').
> 
> There never was anything stated about implicitly DISTINCT - I've always 
seen 
> it as a local API issue where the local API inserts (or has the effect 
of 
> inserting) DISTINCT into all queries.  It was the case the test suite 
> carefully didn't distinguish - except we let such a test case in 
> which is what 
> started all this latest stuff into motion.

Richard Newman has recently brought up this same issue on the -comments 
list. In preparing an answer for him, I looked at the specific text in 
2.3.1 of the Query Results XML Format document:

"""
The distinct attribute indicates that the results are distinct (contain no 
duplicates), such as given by a SPARQL query using SELECT DISTINCT.
"""

To me, this suggests that distinct="true" is only a property of the 
results, and should be included whenever the results contain no 
duplicates, regardless of which--if any--keywords are present in the query 
itself. (I'm not thoroughly positive that this statement in the 
specification implies the opposite, "If the distinct attribute's value is 
false, then the results contain at least one duplicate", but it does seem 
that way to me.)

Do any implementations that we know about behave in this way? (Set 
distinct="true"/"false" solely based on the presence/absence of duplicates 
in the results.)

Lee

> 
> With the introduction of REDUCED, and the algebra, this all looks a bit 
more 
> suspect.  REDUCED is used when the query is unconcerned about 
cardinality. 
> So, by implication only, SELECT without modifier is suggesting complete 
> cardinality.
> 
>    Andy
> 
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Received on Wednesday, 28 March 2007 06:52:14 GMT

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