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Re: Using named graphs to model PROV's Accounts

From: Timothy Lebo <lebot@rpi.edu>
Date: Wed, 12 Oct 2011 00:43:30 -0400
Cc: public-rdf-prov@w3.org
Message-Id: <BB1547C9-E023-4821-A4DC-0839DB80B5FF@rpi.edu>
To: Andy Seaborne <andy.seaborne@epimorphics.com>

On Oct 11, 2011, at 3:32 PM, Andy Seaborne wrote:

> On 11/10/11 19:11, Timothy Lebo wrote:
>> rdf-prov,
>> In preparation for the RDF WG F2F this week, I wanted to provide some discussion on using named graphs to address some provenance modeling.
>> I have updated http://www.w3.org/2011/prov/wiki/Using_named_graphs_to_model_Accounts to reflect some feedback and extend the discussion on named graphs.
>> In particular, I discuss:
>> * reuse of the SPARQL Service Description vocabulary to describe named graphs.
>> * Meta Named Graph pairs,
>> * a simple application of these to create Cache Graphs
>> * the importance of modeling the "location" of a graph to disambiguate many graphs with the same name.
>> These components are needed to model PROV's notion of Accounts, which permit different agents to assert different views of the same "event" (i.e., ProcessExecution). I hope to wrap up all of this into a final proposal by the end of the week.
>> Any suggestions or comments appreciated.

Thanks for taking a look, Andy. 
I really appreciate your time and consideration.

> As a principle (of AWWW), one name can only refer to one thing.

Absolutely. The problem that I'm trying to highlight is that traditional named graph modeling (from what I have seen) has been "lazy" in the choice of URIs used to name them, inadequately assuming a local scope when referencing them. This laziness _is_ violating the AWWW's only-one-referrent principle.

On the practical side, there is some niceness to naming a local graph with the same name as a graph somewhere else. For example, it's pretty self-evident that  my g-box named <http://www.w3.org/People/Berners-Lee/card> is going to have something to do with another g-box named <http://www.w3.org/People/Berners-Lee/card>, or even the g-snap you stumble upon when you resolve <http://www.w3.org/People/Berners-Lee/card>.

But the straightforwardness of multiple g-boxes with the same name comes with a cost - eyesore URIs.
Some notes on a generic approach to create unique URIs for the g-boxes are at [1], which proposes to tuck a DESCRIBE <NG> into a SPARQL endpoint's namespace. Ugly, but general.
(The writeup isn't as clear as I'd like to to be, and for that I apologize)

> "graph" here seems to refer to graph-a-location but also "graph the contents of the location".  But those are different things.

I agree, they are different.
Is there a better discussion of this distinction, so that I may reference it and reconcile my discussion?

> The RDF-WG has the concept of "graph box" (g-box) which is a thing that hold on "graph-value" (g-snap - snapshot).

I'm happy to adopt this terminology, as it is quite intuitive.

> In RDF a graph is a set of triples and as a set it can not change. ("Set" as in the mathematical kind, not the programming language mutable datastructure).

I'm not sure I've challenged what an RDF graph is; I'm targeting some challenges with the multiple aspects of what a _named_ graph is.
Did I say something that conflicts with the notion of a "vanilla" RDF graph? If so, please let me know where so that I can smooth that out.

Thanks again for your responses. Using your terminology really helps clarify things.

Tim Lebo

[1] https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd:NamedGraph
Received on Wednesday, 12 October 2011 04:44:06 UTC

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