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Re: Go ahead with pub

From: Eric Prud'hommeaux <eric@w3.org>
Date: Tue, 3 Oct 2006 16:11:21 +0200
To: Bijan Parsia <bparsia@cs.man.ac.uk>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-ID: <20061003141121.GA3378@w3.org>

On Mon, Oct 02, 2006 at 10:14:14AM +0100, Bijan Parsia wrote:
> I think the status part should point to the issues list.
> 
> """Costs: Tableau-based reasoners (at least, the Pellet Demo example  
> 7) rely on the current, more expressive semantics to match  
> implications that are not in a materializable RDF graph."""
> 
> No. Pellet uses BNodes as syntax for non-distinguished variables, as  
> that's what we were told was the likely syntax for non-distinguished  
> variables in SPARQL/DL. The semantics of *all* variables in SPARQL/ 
> RDF is semi-distinguished.

But we need to explain to the community, in simple terms, why we
non-distinguished variables.

> I thought the alternative proposal (e.g., from conversation with  
> Jeen, Jorge and others) was to *drop* BNodes in triple patterns. That  
> does solve all the problems of scope, meaning etc., but it means that  
> certain combinations of the axes of distinguishedness will be harder  
> to specify (but heck, we can always introduce syntax later).

The majority of the deployed SPARQL and RDQL implementations follow
the subgraph semantics of [LC1] so I am trying to explain why we have
a different semantics. This includes why we were motivated to use the
E-entailment semantics of [LC2] and test cases [DIF] to show how they
might differ.

Not having BNodes at all seems like a last resort, if we discover that
a large fraction of the community is specifically dis-served by us
keeping them in.

[LC1] http://www.w3.org/TR/2005/WD-rdf-sparql-query-20050721/#BasicGraphPatternMatching
[LC2] http://www.w3.org/TR/2006/WD-rdf-sparql-query-20060220/#BasicGraphPatternMatching
[DIF] http://www.w3.org/mid/20060919134330.GC30275@w3.org

-- 
-eric

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Received on Tuesday, 3 October 2006 14:10:22 GMT

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