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Re: Querying "all graphs" (was: Re: Graph to retrieve DESCRIBE result from)

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Mon, 30 Mar 2009 11:17:35 -0400
To: "Lee Feigenbaum" <lee@thefigtrees.net>
cc: "Kjetil Kjernsmo" <Kjetil.Kjernsmo@computas.com>, "'RDF Data Access Working Group'" <public-rdf-dawg@w3.org>
Message-ID: <C5F65ACF.901C%ogbujic@ccf.org>
I think I'm going to break this out into a separate feature request and try
to better articulate the problem and suggested solutions before we run out
of steam in our current feature review.

> Right, but this just scopes part of the query to the dataset, which has
> already been defined as above. Unless I misunderstand, the feature in
> question is how does a SPARQL user specify that they want to query
> against "all the graphs that the engine could possibly query".

The feature I had in mind was "how does the user specify that they want to
query against all the named graphs of the specified dataset" preferably as a
default graph. So, it is exactly about specifying which subset of the
dataset should be queried and how to carve up such subsets and (possibly)
refer to them by name.

> This sounds like a different feature to me: this sounds like asking for
> some way to treat the named graphs in a data set as a single graph. But
> I don't see any reason for that since you can just use the default graph
> for that - since you already needed to have some way to define the named
> graphs in your data set as containing "all graphs", you could just as
> easily define the default graph as containing "all graphs".

Right, but currently if this is not specified by the user (in some way,
currently FROM ... is the only way) then the server can provide anything for
the default graph (including an empty graph , which is what the tests in the
latest test suite sanction).

The motivation here is that an empty default graph is not quite as useful as
a default graph that (either by default or by specific instruction from the
user) is instead the merge of all the named graphs and it would be nice if
there was an explicit way to specify this w/out relying on the applications
behavior which could differ between systems.

> Well, that's a bit different since everything inside GRAPH ?var { ... }
> needs to match against a single graph from the named graph part of the
> data set.

Yes, I realize that now.  Which means that even this would not work as a
workaround for the need described above (unless the the desired behavior is
to match against a single graph from the named graph).

-- 
----------------------
Chimezie (chee-meh) Thomas-Ogbuji (oh-bu-gee)
Heart and Vascular Institute (Clinical Investigations)
Cleveland Clinic (ogbujic@ccf.org)
Ph.D. Student Case Western Reserve University
(chimezie.thomas-ogbuji@case.edu)


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Received on Monday, 30 March 2009 15:18:27 GMT

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