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Re: Minimal dataset semantics

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 24 Aug 2012 10:58:24 -0500
Cc: Sandro Hawke <sandro@w3.org>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <67783DA4-68DE-4231-9D93-6CBC8BA470B2@ihmc.us>
To: Richard Cyganiak <richard@cyganiak.de>

On Aug 23, 2012, at 2:43 PM, Richard Cyganiak wrote:

> On 23 Aug 2012, at 19:02, Pat Hayes wrote:
>>>> b) to define a minimal version of a "truth-based"/"entailment-based" semantics (where [[ :i1 { G } ]] entails [[ :i1 { G' } ]] if graph G entails graph G').
>> 
>> Which means that the "name" refers to the entailment closure of the graph, rather than the graph itself. Right? 
> 
> I'm not sure what you mean by "refers to".

refers to = denotes (= names, anywhere outside the W3C :-)

> 
> Regarding the formal mechanism of associating IRIs with their respective graphs, I've started to like the idea that Alan mentioned the other day: Dataset interpretations contain a mapping from resources to graphs, called the graph extension. This mapping associates graphs with (some) resources. A name-graph-pair (a.k.a. abstract named graph) <i,G> satisfies a dataset interpretation I if the graph extension in I of I(i) entails G.

I am cool with that, although it does have some consequences that y'all might find odd when you try mixing it with owl:sameAs. Do you want this:

:a owl:sameAs :b
{ :a { :this :is :graph}}

to entail 

{:b {:this :is :graph}}

?

> 
> If I'm not messing up, then this mechanism works the same as the property extension and class extension mechanisms that already exist in RDF Semantics.

Its in the same spirit, one might say, yes. The difference is that property and class extensions are kind of abstractions, so it is (maybe with a slight forcing, but one gets used to it) OK to say in those cases that the resource *is* the class or property; but in this case, I think that to identify the resource with the graph would be too much of a stretch (and would negate the intended use cases, in any case). So its not *exactly* similar, in practice. 

> 
> So, the graph IRI then *denotes* a resource (one that is in the domain of the class extension function). And in the abstract syntax, the graph IRI is "associated" or "paired" with a certain RDF graph.

The IRI or the resource is paired with it? I think its the denoted resource, yes?

> I don't know if one can say that the IRI "refers to" the entailment closure of the graph.
> 
> Does this make any sense?

Yes, it makes good sense. I would avoid saying that the IRI denotes the graph, in this case. ITs rather that there is relation beween them, we need a name for it, lets say that the IRI "indicates" the graph. That is, I indicates G whern I denotes X associated with G

Why do you want to have entailment closures rather than graphs? Bear in mind that a simple bug in a graph can make the RDFS or OWL entailment closure be infinite. I think precision outweighs convenience here. 

Pat


> 
> Best,
> Richard
> 

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Received on Friday, 24 August 2012 15:58:57 UTC

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