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Re: problem with blank nodes in EXISTS solution mappings

From: Gregory Williams <greg@evilfunhouse.com>
Date: Thu, 16 Jun 2016 15:44:42 -0700
Cc: public-sparql-dev@w3.org
Message-Id: <FF463E78-B1B6-4C0D-B2BC-B2E77E81FBEB@evilfunhouse.com>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
On Jun 16, 2016, at 3:38 PM, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
> 
> The definition of EXISTS in SPARQL 1.1 Query uses the substitute function.
> There are multiple problems with substitute already reported.  Here is
> another one.
> 
> 
> Consider
> 
> SELECT ?x WHERE {
>  :s :p ?x .
>  FILTER EXISTS { ?x :p ?y . }
> }
> 
> on the graph
> 
> :s :p _:x .
> 
> The EXISTS gets { { (x,_:x) } } and then does a substitute which results in
>  BGP( _:x :p ?y )
> This has a solution of
>  { { (y,:x) } }
> because the blank node that is the mapping of x can itself be further mapped
> to :s in the RDF instance mapping part of a pattern instance mapping.

Peter,

Can you expand on why you believe "the blank node that is the mapping of x can itself be further mapped to :s”? I’m not sure I follow.

thanks,
.greg
Received on Thursday, 16 June 2016 22:45:07 UTC

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