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question about combining patterns

From: Alberto Reggiori <alberto@asemantics.com>
Date: Wed, 2 Feb 2005 12:22:32 +0100
Message-Id: <4efc0fecec70562b164a32cdc5dec98f@asemantics.com>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>


hi all,

I have small question about an example I came up to test grouping

Given the following data:

<http://example.org/book/book1> <http://purl.org/dc/elements/1.1/title> 
"SPARQL Tutorial" .
<http://example.org/book/book1> <http://example.org/ns#price> 
"42"^^<http://www.w3.org/2001/XMLSchema#integer> .
<http://example.org/book/book2> <http://purl.org/dc/elements/1.1/title> 
"The Semantic Web" .
<http://example.org/book/book2> <http://example.org/ns#price> 
"23"^^<http://www.w3.org/2001/XMLSchema#integer> .

is the following query

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>
PREFIX  ns:  <http://example.org/ns#>
SELECT  ?title ?price
WHERE
{
    ( ?x dc:title ?title )
    ( ?x ns:price ?price )
}
AND ( ( ?price < 30 ) || ( ?price > 40 ) )

going to fail accordingly to what stated in

	http://www.w3.org/2001/sw/DataAccess/rq23/#CombiningPatterns

?

I think so - due the above query has two graph-patterns, and that the 
constraints by definition do not bind any var - it should fail

While the following query would succeed

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>
PREFIX  ns:  <http://example.org/ns#>
SELECT  ?title ?price
WHERE
( ?x ns:price ?price )
{
    ( ?x dc:title ?title )
}
AND ( ( ?price < 30 ) || ( ?price > 40 ) )

due that the first (top most) graph-pattern binds ?x and ?price 
accordingly

In other words, in the implementation, while processing the blocks 
stack one should execute any "binding graph-pattern" first or fail if 
not possible.

is this the correct behavior?

thanks

Alberto

-
Alberto Reggiori, @Semantics S.R.L.
www.asemantics.com
Received on Wednesday, 2 February 2005 11:22:38 GMT

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