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Re: why I don't like named graph IRIs in the DATASET proposal

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Tue, 04 Oct 2011 22:48:28 +0200
Message-ID: <4E8B711C.80906@liris.cnrs.fr>
To: Richard Cyganiak <richard@cyganiak.de>
CC: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
Richard,

On 10/04/2011 05:08 PM, Richard Cyganiak wrote:
> On 2 Oct 2011, at 18:06, Pierre-Antoine Champin wrote:
>> As you stress it, RDF does not dictate which IRI should denote
>> which resource (including graphs). I don't think I ever suggested
>> to change that.
>> 
>> However, RDF dictates that each time I use the same IRI (as a
>> node), it denotes the same resource.
> 
> No, it doesn't.
> 
> RDF Semantics is concerned with the interpretation of *individual RDF
> graphs*.

Well, that's what I meant.

> As far as RDF Semantics is concerned, the same IRI may identify
> completely different things in different RDF graphs.
> 
> It is the social contracts and conventions of the web that encourage
> us to converge on a single unique referent for each IRI. This is
> orthogonal
> 
> For example, in this triple:
> 
> <#me> foaf:homepage <http://richard.cyganiak.de/>.
> 
> we all know what the subject of the encoded statement is. But that's
> not because of RDF Semantics. As far as RDF Semantics is concerned,
> <http://richard.cyganiak.de/> denotes a completely arbitrary
> resource. It's conventions that allow us – and the software we create
> – to understand that the target is a web page that can be accessed
> via a browser and so on.
> 
> This mechanism *works*.

200% agreed.

> I suggest to treat graph names in exactly the same way.

It depends how you define "the same way".

IRIs currently must be used consistently inside a single graph. I was
assuming that this principle would extend to datasets, should we define
them in the RDF spec.

>From your response to my messages and Pat's, I now understand that you
do not want to go that far.

> When we assert inside some RDF dataset:
> 
> <#me> ex:assertsGraph <#graph1>.
> 
> then as far as RDF Semantics is concerned, <#graph1> denotes an
> arbitrary resource. It's conventions – and the definition of
> ex:assertsGraph – that allow us, and our software, to understand that
> this talks about a different graph within the same dataset.
>
> When you and Pat demand that the denotation of graph names in RDF
> datasets be fixed to the graph, then you conveniently ignore the fact
> that RDF Semantics currently doesn't have the power to fix the
> denotation of *anything* (except the RDF(S) built-ins),

and all literal values...

> and *always*
> defers to convention for establishing the connection between IRIs and
> things. RDF works nevertheless. Why should it be any different for
> graphs?

Well, if graphs in a dataset are g-snap, then they look very much like
literals to me, and I would tend to read

  <some-uri> { :a :b :c }

as something like

  <some-uri> owl:equals " :a :b :c . "^^rdf:turtle

(if I may indulge in my former proposal...).
In that case, it does indeedfix the semantics of <some-uri>, but not
more than

  <the-answer> owl:equals 42 .

does. This already works in RDF (well OWL-full...).


Now, if graphs are g-boxes, I would rather read

  <some-uri> { :a :b :c }

as something like

  <some-uri> rdf:hasCurrentGSnap [
	log:implies " :a :b :c . "^^rdf:turtle
  ]

where rdf:hasCurrentGSnap would have rdf:GBox as its domain, so I can
*at least* infer that <some-uri> denotes *some* g-box.

In any case, I do not see how what I propose implies something radically
different from the kind of inference that already exist in RDF.

Let's discuss this tomorrow.

  pa

> 
> Best, Richard
Received on Tuesday, 4 October 2011 20:49:04 GMT

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