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

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 15 Oct 2007 15:32:34 +0100
Message-ID: <47137A02.4000705@hp.com>
To: "Ogbuji, Chimezie" <OGBUJIC@ccf.org>
CC: public-rdf-dawg@w3.org



Ogbuji, Chimezie wrote:
> 
> 
> 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,

This text introduces some new terminology - I only found one reference on the 
web to "surface notation" in the context of RDF (a note by Pat).

Isn't the indirection due to the mention of the IRI twice and the use of a 
graph in the dataset.

How about: for 8.2.3:

[[
The actions required to construct the dataset are not determined by the 
dataset description.  If an IRI is given twice in an dataset description, 
either by using two FROM clauses, or a FROM clause and a FROM NAMED clause, 
then it does not assume that exactly one or exactly two attempts are made to 
obtain an RDF graph associated with the IRI.  Therefore, no assumptions can be 
made about blank node identity in triples obtained from the two occurrences in 
the dataset description.
]]

	Andy
Received on Monday, 15 October 2007 14:56:14 GMT

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