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Re: Comments on TF-Graphs/Minimal-dataset-semantics

From: Ivan Herman <ivan@w3.org>
Date: Tue, 18 Sep 2012 12:17:02 +0200
Cc: RDF comments <www-rdf-comments@w3.org>, Graham Klyne <graham.klyne@zoo.ox.ac.uk>
Message-Id: <139A4A79-A7F3-444B-9CB5-D0C4E998D3D6@w3.org>
To: Graham Klyne <GK@ninebynine.org>
Hi Graham,

some questions...

On Sep 18, 2012, at 11:22 , Graham Klyne wrote:

> Ref. http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics
> 

[snip]

> 
> 
> DD4, DD5: http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics#DD4:_Does_the_graph_extension_assign_graphs_to_resources_or_to_IRIs.3F
> 
> I'm treating these together, because I think my response to DD5 renders DD4 somewhat moot.
> 
> I think it would be very useful if a graph name n *does* denote the IGEXT(n) graph, as this would provide a hook for future semantic extensions.  In the context of provenance, we want to be able to express contexts/situations that are specializations of other (e.g. when talking about a web document on a particular date as a particular instance of that document during a particular year).  While I would not (necessarily) expect the specifics of such a mechanism to be part of the RDF Dataset semantics, having a name for talking about the graphs leaves open the possibility of introducing new properties with their own extension semantics.  The inconsistencies that would arise if the URI is used as some other kind of resource seem to me to be quite benign (i.e. "don't do that").
> 

I am not sure I understand the argumentation. 

The present proposal has a strong analogy to the way properties are modeled in the current RDF semantics. If a property has the URI 'p', 'p' does not 'denote' that property, because I(p) is not set of pairs itself but, rather, IEXT(I(p)) is. That provides a smoother way to talk about 'p' or I(p). The current IGEXT approach has a full analogy to this; I(g) is not a graph, but IGEXT(I(g)) is. 

What you favour would mean that the IGEXT is defined on the URI-s themselves. Why would that "...would provide a hook for future semantic extensions" as opposed to the current situation? For practical purposes 'n', in a named graph is, shall we say, 'associated' with the graph, and that seems to be enough for the kind of additional properties you are referring to. Again, just as it is perfectly possible to make all kinds of statement on property 'p', in spite of the fact that, strictly speaking, 'p' does not denote the Property either...


> BUT: this begs a further question: is there any way to refer to the default graph (or some graph that entails the default graph) in an RDF Dataset?
> 

Not that I know of.

Ivan

----
Ivan Herman, W3C Semantic Web Activity Lead
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Received on Tuesday, 18 September 2012 10:17:30 GMT

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