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Re: Using named graphs to model PROV's Accounts

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 4 Oct 2011 15:21:46 +0100
Cc: public-rdf-prov@w3.org
Message-Id: <DAE491E2-4621-4E40-9DCA-29344334F896@cyganiak.de>
To: Timothy Lebo <lebot@rpi.edu>
On 3 Oct 2011, at 00:47, Timothy Lebo wrote:
> I have written an initial proposal [1] for how to use RDF named graphs and PROV's OWL encoding to represent PROV's notion of an Account.

Nice work!

Some comments:

“They are a feature of the non-standard N3 language [7] and are not widely used, perhaps because of verbosity and size considerations.” – N3 itself isn't widely used or implemented. That's sufficient explanation for the scarceness of graph literals. I'm not sure there's enough evidence to pinpoint specific reasons such as  “verbosity and size”.

“Named graphs surface in a variety of ways.” – I'd add another way: an RDF file published under a URI can be seen as a named graph in a global, web-wide named graph set.

“Sameness of named graphs” – The entire section seems questionable to me. It is true that nothing stops us from using the same graph name with different contents in different datasets, but this is equally true of any URI anywhere in RDF. As far as RDF Concepts and RDF Semantics are concerned, the URI ex:foo might represent one thing RDF graph G1 and something else in RDF graph G2 – it is only the social contracts and conventions around URI ownership and web architecture that discourage such behaviour and allow us to maintain the fiction that URIs in RDF actually identify specific entities. The same could be said of graph names.

I'm sceptical about the assertion that a named graph's “last modified time” contributes to its identity. In the example, the last modified time of the individual graphs is unknowable. It perhaps makes sense to talk about a last modified name of the enclosing TriG file, but not of the graphs themselves.

Instead of speaking of a graph's “location”, it might be more accurate to speak of the “RDF dataset” it is in. The term is defined in the SPARQL spec.

All the best,
Richard



> This is oriented towards the PROV WG, so the background on named graphs may have too much discussion for the RDF WG.
> Regardless, I'd appreciate any pointers to appropriate work, or feedback on my pragmatic perspective on how named graphs grew up and work.
> 
> I've set up the background and the initial example, but ran out of steam to finish the example with the solution.
> 
> Regardless, I think it is at a good point for some early review.
> 
> Of course, you could suggest your own solutions to the problem!
> 
> Thanks for your consideration.
> 
> Regards,
> Tim Lebo
> 
> [1] http://www.w3.org/2011/prov/wiki/Using_named_graphs_to_model_Accounts
Received on Tuesday, 4 October 2011 14:22:29 GMT

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