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Endpoint URLs as special dataset IRIs - Was Re: Querying "all graphs"

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Mon, 30 Mar 2009 19:54:15 -0400
To: "Seaborne, Andy" <andy.seaborne@hp.com>, "Lee Feigenbaum" <lee@thefigtrees.net>
cc: "Kjetil Kjernsmo" <Kjetil.Kjernsmo@computas.com>, "'RDF Data Access Working Group'" <public-rdf-dawg@w3.org>
Message-ID: <C5F6D3E7.9062%ogbujic@ccf.org>
This is purely anecdotal, but meant to inform this thread regarding Querying
"all graphs" and allowing services to interpret the IRIs in dataset clauses
in special ways.

I recently wanted to use an OWL editor (with a SPARQL composer) to compose
SPARQL queries and dispatch it against a SPARQL service I setup.  I was told
that in order to do this, rather than configure the editor to tell it which
location to send the queries to I had to add:

FROM <..URL of endpoint..>

to the query, so both the client and the server interpret the use of FROM
clause.  For the client, it uses this to determine where to 'send' the query
(I'm not sure if this a fair reading of SPARQL).  For the service, it
assumes dataset IRIs that refer to the service can be ignored.

At first, I thought this was not the best way to do this, but upon closer
reading of the specification, this *seems* to be allowed, since the service
could determine that it is the resource identified by the endpoint URL and
thus answering the query using the system-level dataset is tantamount to
creating the default graph out of whatever representation might be returned
from the endpoint URL (even though resolving the endpoint URL over HTTP
would  return an HTML form, for instance).

However, in order to have my service properly answer to queries composed and
dispatched from this editor, I had to change the functionality such that
whenever the default dataset IRI is the location of the endpoint, the result
is essentially a 'no-op'.  Prior to making this change, my service was
actually trying to resolve the endpoint URL in order to get a graph
representation, parse the representation (in this case it wasn't able to
parse the HTML form), and evaluating the query against an empty graph.

If there were some best practices about such liberties services can take
with 'interpreting' IRI in FROM / FROM NAMED it might help guide making such
a change to a service implementation in order to be able to align its
understanding of endpoint URLs with that of this particular client.

----------------------
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 23:55:03 GMT

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