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Re: Making progress on graphs

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 23 May 2012 06:26:46 -0500
Cc: Guus Schreiber <guus.schreiber@vu.nl>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <35686EB3-5B8A-4855-A4A8-1F77308F04E4@ihmc.us>
To: Richard Cyganiak <richard@cyganiak.de>
Sorry, this was very brief. Longer reply here.

On May 22, 2012, at 8:06 PM, Pat Hayes wrote:

> 
> On May 22, 2012, at 10:35 AM, Richard Cyganiak wrote:
> 
>> On 22 May 2012, at 16:00, Pat Hayes wrote:
>>>>>>>> ISSUE-28 Syntactic nesting of g-texts http://www.w3.org/2011/rdf-wg/track/issues/28
>>>>>>>> PROPOSED: Close ISSUE-28 ("Do we need syntactic nesting of graphs (g-texts) as in
>>>>>>>> N3?"), saying No, we do not -- they are useful, but we can provide the same
>>>>>>>> functionality with datasets.
>>>>>> 
>>>>>> Let's assume the abstract syntax supported nested graphs. Then we can convert that to a “flat” dataset like this: For any nested graph G, replace it by a new IRI i, and add a new pair <i,G> to the dataset.
>>>>> 
>>>>> I was afraid of that. That works only if we give the datasets a semantics in which the graph 'name' really does denote the named graph, in the 2004 semantics sense of 'denote'.
>>>> 
>>>> Why? Can you give an example where this does not work?
>>> 
>>> […T]he 2004 specs say that when an IRI appears in a triple, the truth of the triple depends upon what the IRI *denotes*. So if the IRI denotes something else, or has some other relationship to the graph (or both), then using that IRI inside some RDF isnt going to refer to the named graph at all.
>> 
>> But I didn't say that I want to refer to a named graph. I want to refer to a resource. That resource is associated in some way with the RDF graph (I'm trying to call this association the “state relationship” or rdf:state, as described in the other ongoing thread).
>> 
>> So, the pair <i,G> states that the denotation of i is associated with G. Any triples involving i thus refer to the thing associated with G. That's, I believe, all we need to “flatten” a “nested” abstract syntax into an RDF dataset.
>> 
>> How exactly this association works formally, or if it is formally defined at all, is a valid question, but one that seems orthogonal to ISSUE-28 above.

I disagree with the orthogonality. In order for the reduction of nested graphs to datasets, claimed in the issue-28 resolution, to actually work, the relationship of IRIs to what they name has to be able to reproduce the relationship between an enclosing graph and a graph nested inside it. I will confess that I don't know exactly what the second, nesting, relationship was supposed to be with any precision, but it does seem (??) to be a relationship between actual graphs. If the datastore-naming relationship does not connect names to graphs, then I don't see how it can faithfully reprodice the nesting relationship. Maybe I am muddled about this: maybe the nesting relationship itself was really one between graph-resources all along, or maybe there is some clever way to weave a nesting-imitating relationship by composing resource-naming with HTTP access, or the like. But until this is explained in some more detail, and we have all understood how it works, I don't think we can take the risk of deciding issue 28. Because until this is done, we really have no idea if this claimed flattening reduction is actually going to work. The devil is in the details here. 

Pat


>> 
>>> In a nutshell: if you want to use the graph names to refer to the graph, then they must actually refer to the graph. 
>> 
>> I don't want them to refer to the graph. I want them to refer to a resource that is associated with a graph.
> 
> Then the proposed conversion does not work. The IRI will refer to something. That thing will be what is being talked about in the RDF triple using that IRI. If that thing is not the graph, then something is wrong. No, we cannot solve issue-28 now and clean this up later. 
> 
> Pat
> 
>> 
>> Best,
>> Richard
>> 
> 
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> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Wednesday, 23 May 2012 11:27:31 GMT

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