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Re: subgraph/entailment

From: Dan Connolly <connolly@w3.org>
Date: Wed, 07 Sep 2005 08:19:50 -0500
To: Bijan Parsia <bparsia@isr.umd.edu>
Cc: Enrico Franconi <franconi@inf.unibz.it>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1126099190.16011.1033.camel@dirk>

On Tue, 2005-09-06 at 23:35 -0400, Bijan Parsia wrote:
> On Sep 6, 2005, at 10:35 PM, Dan Connolly wrote:
> 
> > On Wed, 2005-09-07 at 03:47 +0200, Enrico Franconi wrote:
> > [...]
> >> Now we have three possibilities:
> >
> > I'm getting lost.
> 
> To pick up the dialectic as I understand it, Enrico thought (as many do 
> on first reading) that the subgraph language *precluded* extending 
> SPARQL to query datasets expressed in more expressive logics than 
> RDF/RDFS (while respecting the semantics of those logics).

Yes, as designed, it does. The way more expressive logics fit into
this design is that they contribute to the graph that's being
queried against...

> > It's already possible for a server to chose the deductive closure
> > of the original information as its background graph.
> 
> Pointer please?

"These triples can come from a variety of sources. For instance, they
may come directly from an RDF document. They may be inferred from other
RDF triples."
 -- http://www.w3.org/TR/rdf-sparql-query/#introduction

See also our discussion of serviceDescription; i.e. ways that a
server can advertise what dataset it uses...
  http://www.w3.org/2001/sw/DataAccess/issues#serviceDescription

We decided that's not ready for standardization just yet.

[...]
> 
> Er...so SPARQL is defined only for RDF graphs without their semantics? 
> Or, rather, only against the *asserted* triples in an RDF graph?

Yes.

> This isn't happy!

We have a growing body of experience that says it's happy enough for v1;
the design meets all the WG's requirements do date; 4 or 5
implementors have coded up this design without complaint, and a
modest number of fielded services seem to meet user expectations.

http://esw.w3.org/topic/SparqlImplementations
http://esw.w3.org/topic/DawgShows

> Of course, you could just restrict yourself to asserted triples. My org 
> will probably object, though.

We have already restricted ourselves to asserted triples.
Your org already agreed to the present design. There are probably
other relevant decisions that you're party to, but the recorded
decision that's easiest for me to find is when we decided, 28 June,
to go to last call.
 http://www.w3.org/2005/06/28-dawg-minutes#item09

There is perhaps new information that motivates reconsidering
the design. Perhaps you could elaborate on "This isn't happy."

[...]



> Have we met the charter if we can't query (or have runaway bad query) 
> for graphs closed under RDF entailment?

I suggest we leave the charter aside for a bit. If a critical mass
of the WG supports some new requirements, and those requirements
conflict with the charter, we'll look at ways to resolve that conflict,
including modifying the charter.


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Wednesday, 7 September 2005 13:20:01 GMT

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