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Re: subgraph/entailment

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Tue, 6 Sep 2005 21:13:09 -0400
Message-Id: <c2691a3107793da12be45607e63d7043@isr.umd.edu>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Enrico Franconi <franconi@inf.unibz.it>

On Sep 6, 2005, at 8:25 PM, Enrico Franconi wrote:
[snip]
> Aha, then SPARQL computes the subgraph over the infinite *deductive 
> closure* of the original RDF graph, and not only over one completion. 
> Now I see it. Of course, in the case of RDF, since it enjoys the 
> minimal model property, there is only one (finite) completion, and 
> this coincides with the deductive closure. That's why the problem 
> didn't show up if we just have RDF. Thanks for this clarification!
[snip]

No problem. It took some wrangling with Pat for me to get what he meant.

There is another approach, allow SPARQL queries for more expressive 
languages to work.

Hmm. Did I send this to the list? Oh well, it's late. Forgive me if I 
have.

Looking again at the charter:
""""1.8 Derived Graphs

The working group must recognize that RDF graphs are often constructed 
by aggregation from multiple sources and through logical inference, and 
that sometimes the graphs are never materialized. Such graphs may be 
arbitrarily large or infinite."""

Another way to look at this is that for some forms of "logical 
inference" (the kind which generates a model), it's not just the case 
that the graphs are never materialize, or arbitrarily large, or 
infinite, but there might be *multiple* such graphs generated from the 
same "base".

So lets say you forget about deductive closure and focus on what I'm 
going to call "ABox completion", where each ABox is an RDF Graph 
generated by completion rules. Then you can sparql query by subgraph 
*that*. Now, a hit has to be defined by the binding being found in 
*ALL* completions.

Each ABox corresponds to a model. Ergo, we are back to entailment 
without much fuss.

This might be an easier for a class of folks to understand than the 
deductive closure way.

Er....am I backing myself into an action about this? Should we consider 
a separate section or document?

I'd really like to see SOME clarification so that OWL folks jump on the 
SPARQL bandwagon. There is a *lot* of energy going into query answering 
in OWL-DL land.

Cheers,
Bijan.
Received on Wednesday, 7 September 2005 01:13:13 GMT

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