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Text for clarification of re-use of IRIs in dataset clauses

From: Ogbuji, Chimezie <OGBUJIC@ccf.org>
Date: Thu, 11 Oct 2007 15:14:44 -0400
Message-ID: <2702D0EBA4F0A749968E52E8644184EA28880C@CCHSCLEXMB59.cc.ad.cchs.net>
To: public-rdf-dawg@w3.org
Per my action [1] to propose text to clarify that not all graphs in the dataset need to be disjoint/distinct.  The text below is meant to extend the last paragraph of 8.2.2 Specifying Named Graphs.  This seemed to be the best place for the clarification.  I tried to cover the general ambiguity.

The FROM NAMED syntax suggests that the IRI identifies the corresponding graph, but the relationship between an IRI and a graph in an RDF dataset is indirect. The IRI identifies a resource, and the resource is represented by a graph (or, more precisely: by a document that serializes a graph). The relationship between the IRI and the representation is subject to time, an intermediate caching policy, the query service, and the mechanics of the underlying transport protocol.  For further details see [WEBARCH].  

The distinction between a surface RDF notation and the abstract RDF graph which results from parsing an instance of the surface notation is an additional indirection.  As a consequence of these things, the repeated use of an IRI in either the same dataset clause, across dataset clauses, or across whole SPARQL queries can feasibly result in either the formulation of a single canonical graph, separate but isometric graphs, or completely disjoint [2] RDF graphs for each use of the same IRI.

[1] http://www.w3.org/2007/10/09-dawg-minutes.html#action14
[2] http://www.w3.org/TR/rdf-concepts/#section-graph-equality

Chimezie (chee-meh) Ogbuji
Lead Systems Analyst
Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
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Received on Thursday, 11 October 2007 19:15:20 UTC

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