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Re: subgraph/entailment

From: Dan Connolly <connolly@w3.org>
Date: Wed, 07 Sep 2005 08:43:45 -0500
To: Bijan Parsia <bparsia@isr.umd.edu>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1126100626.16011.1041.camel@dirk>

On Wed, 2005-09-07 at 09:27 -0400, Bijan Parsia wrote:
> On Sep 7, 2005, at 9:19 AM, Dan Connolly wrote:
> 
> > 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...
> 
> [snip]
> >> Er...so SPARQL is defined only for RDF graphs without their semantics?
> >> Or, rather, only against the *asserted* triples in an RDF graph?
> >
> > Yes.
> [snip]
> 
> This is a contradiction (I think we have a terminology conflict). The 
> contribution of more expressive logics cannot be asserted triples. By 
> "asserted" I meant, "asserted in the original document/dataset" not 
> "asserted 'by inference'".

Er... "original" is a distinction that's not visible to SPARQL QL.

In SPARQL QL, you start with some RDF dataset (i.e. a bunch of
graphs). How you got there is your business, but we expect
one of the popular ways is by grabbing data off the web and
computing, say, the RDFS closure of it.

The specification of SPARQL QL and our test harness and such
start there, and tell you, given a query, what the results are.

("original" is perhaps visible from the protocol, and perhaps
in the bits of the protocol that leaked into the QL, i.e.
FROM and FROM NAMED, and certainly
would have been visible in serviceDescription stuff like SADDLE.
But I'm hoping we can leave that aside for this discussion.)

> If the way around this is to do some sort of closure and then "dump" 
> the data (roughly) and reload it..well....now we're requiring 
> extrasilly gyrations to kill clarity and avoid some important details.

You don't have to dump it anywhere; you don't even have to
pre-compute the whole thing; you can do the query backward-chaining
style, if you like.

> 
> Cheers,
> Bijan.
-- 
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 13:43:59 GMT

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