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Re: Named Graphs (was RE: Reification - whats best practice?

From: Phil Dawes <pdawes@users.sf.net>
Date: Mon, 13 Sep 2004 19:49:00 +0000
Message-ID: <16709.63916.480203.312622@gargle.gargle.HOWL>
To: <Patrick.Stickler@nokia.com>, Jeremy Carroll <jjc@hplb.hpl.hp.com>, <www-rdf-interest@w3.org>

Hi All,

I've re-read the Named Graphs paper, had a bit of a think, and I'm
having difficulty in deciding how best to manage graphs in an rdf store.

In RDF, a URI identifies a resource. In a consistent view, if 2
resources have the same URI, they are the same resource.

In Named Graphs, the URI doesn't identify the Named Graph AFAICS. The
named graph is the set {URI, g} (where g is the graph of triples), and
in a consistent view it is legal to have 2 different named graphs with
the same URI (correct?).

This means I can't use RDF to reason about named graphs (at least not
without some sort of transformation), since I can't use the URI to
identify them.

Is this correct?



Phil Dawes writes:
 > Hi Patrick,
 > Patrick.Stickler@nokia.com writes:
 >  > 
 >  > Since named graphs are named by URIs, one can say what one
 >  > likes about them.
 > Something Steve Harris mentioned to me at foaf-galway and got me
 > thinking: 
 > If named graphs are identified by URI, what do you do when you get 2
 > graphs with the same URI?
 > I'm in the process of developing a store that handles graphs (amongst
 > other things), and have found this crops up quite a lot.
 > e.g. somebody publishes a graph, and then publishes it again slightly
 > ammended with the same URI. Or you get the same graph from 2 different
 > sources (e.g. quoted from 2 different documents), but can't guarantee
 > that they're the same.
 > AFAICS the best solution appears to be to store the graph with an
 > extra layer of indirection - e.g. name the graph with a bnode, and
 > then have properties of the bnode that identify the graph (one of
 > which could be a URI). This allows multiple graphs with the same URI
 > to be stored (but not uniquely identified). Other metadata assocated
 > with the graph could then be used to differentiate them (e.g. source,
 > datestamp).
 > Is there a better solution to this problem?
 > Cheers,
 > Phil
Received on Monday, 20 September 2004 15:30:49 UTC

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