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Bnode names in the answer

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Thu, 26 Jan 2006 12:35:40 +0100
Message-Id: <E75FA42C-5DD8-47F0-A94B-126E40D18D03@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Andy Seaborne <andy.seaborne@hp.com>

On 26 Jan 2006, at 12:22, Enrico Franconi wrote:
> Since now you changed the text to have G no more equal to G', the  
> following does not hold anymore:
> """
> A pattern solution can then be defined as follows: to match a basic  
> graph pattern under simple entailment, it is possible to proceed by  
> finding a mapping from blank nodes and variables in the basic graph  
> pattern to terms in the graph being matched; a pattern solution is  
> then a mapping restricted to just the variables. Moreover, the  
> uniqueness property of pattern solutions guarantees the  
> interoperability between SPARQL systems: given a graph and a basic  
> graph pattern, the set of all the pattern solutions is unique.
> """
> So, if you want to keep the change, in both cases you have to add  
> "modulo arbitrary renamings of the bnodes".
> Still, I argue that the change shouldn't have been made.

What puzzles me, in addition to what I did say in <http:// 
lists.w3.org/Archives/Public/public-rdf-dawg/2006JanMar/0282>, is  
that also the following statement becomes false:

When using simple entailment, the operation of querying an RDF graph  
provides access to the graph structure; nothing that is not already  
in the graph G needs to be inferred or constructed, even implicitly.

This is false since now we allow for some semantics to sneak in: it  
says that graphs are (logically) equivalent if they have different  
bnode names.

If I understand the main motivations of this first version of SPARQL,  
this should not happen. We have just syntax in this version of  
SPARQL. So, we should really have G=G' in the definition of SPARQL  
Basic Graph Pattern Matching.


Received on Thursday, 26 January 2006 11:35:46 UTC

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