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Re: DISTINCTness of literals

From: Eric Prud'hommeaux <eric@w3.org>
Date: Mon, 25 Sep 2006 21:48:13 +0200
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-ID: <20060925194813.GA5350@w3.org>

On Mon, Sep 25, 2006 at 11:22:10AM +0100, Seaborne, Andy wrote:
> 
> We left open what to do about literals of the same value in DISTINCT 
> results.
> 
> I propose that term-distinct apply to literals, and not a form of 
> value-distinct.

+1, for all the resasons that you mention below, plus one can
postprocess to get value-distinct.

> SPARQL is defined for simple entailment anyway so for this entailment 
> regime it would be term-distinct for literals.  I propose that rq24 only 
> talk about this.

+1 as I am in favor o
This will make it much easier to implement in simple SQL store, and 

> Some considerations:
> 
> 1/  It's terms that are returned, not values, when encoded into the result 
> set.  But which term should be returned if two literals are value-distinct 
> and not term-distinct?
> 
> e.g.
> 
> "1"^^xsd:integer
> "01"^^xsd:integer
> "1.0"^^xsd:decimal
> 
> The SPARQL test suite is based on RDF graph equality [1] which uses term 
> equality for literals.
> 
> 
> 2/ XPath/XQuery Functions&Operators [2] allows numeric type promotion - but 
> XML schema datatypes does not and double/float/decimal have different value 
> spaces.  See [3].
> 
> "1.3"^^xsd:double != "1.3"^^decimal
> 
> 
> I've checked in a test [4] for literal distinctness.
> 
> 	Andy
> 
> [1] http://www.w3.org/TR/rdf-concepts/#section-graph-equality
> [2] http://www.w3.org/TR/xpath20/#promotion
> [3] http://www.w3.org/TR/swbp-xsch-datatypes/
> [4] http://www.w3.org/2001/sw/DataAccess/tests/data/Distinct/
> 

-- 
-eric

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Received on Monday, 25 September 2006 19:48:07 GMT

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