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Re: New Proposal (6.1) for GRAPHS

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Mon, 02 Apr 2012 21:46:21 +0100
Message-ID: <4F7A101D.2000009@epimorphics.com>
To: public-rdf-wg@w3.org
Take 2:

(pressed "send",  not "save" ... sigh ...) try again:

On 02/04/12 16:36, Sandro Hawke wrote:
> On Thu, 2012-03-29 at 09:25 -0700, Charles Greer wrote:
>> I really like this solution and it seems to satisfy the use cases
>> familiar to me from when I actually worked a lot with RDF in the wild.
>>
>> One thing I'm tripping over though --  The scope of a TRIG document or
>> RDF dataset in effect 'closes the world.'  Is the idea of "merge" only
>> within a TRIG document/dataset?
>>
>> I can only see two ways to really assert a graph literal -- either by
>> sanctifying the boundaries of  a dataset, thereby making merges with
>> external data problematic, or by signing bytes.  Am I missing something,
>> as usual?
>
> There's some misunderstanding here, yes.   Maybe you can talk through
> some particular thing you imagine doing, involving merging and TriG, and
> I'll be able to pick it up.   From what you've written, I'm confused.
>
> Maybe I can clarifying by translating this TriG document:
>
>          <u1>   {<a>   <b>   <c>  }
>
> into this English declaration:
>
>          The URI 'u1' denotes something, and that thing has exactly one
>          associated RDF Graph.   That associated RDF graph consists of
>          one RDF triple, which we can write in turtle as "<a>  <b>  <c>".


Clearer, but not what I would have expected.

Why "exactly one associated RDF Graph"?

RDF is all about partial descriptions of things.

If
   <u>  { <a>   <b>   <c> . <x>   <y>   <z> . }

then I'd have expected
   <u>  { <a>   <b>   <c> }
and also
   <u>  { <x>   <y>   <z> . }

I guess the concrete examples will help - the choice of URI scheme for
<u> and it's scope becomes very important - it's be clearer to me 
exactly what is being labelled and how.

> So, perhaps it's more clear, now.  If you merged that with another TriG
> document:
>
>          <u1>   {<a>   <b>   <d>  }
>
> Then, trying to accept both documents at onces, you'd be saying:
>
>          The URI 'u1' denotes something, and that thing has exactly one
>          associated RDF graph.  In one document that associated graph is
>          claimed to be the RDF triple "<a>  <b>  <c>", but in another
>          document that graph is claimed to be the RDF triple "<a>  <b>
>          <d>".
>
> So, in this case, you can try to merge the documents, but when you do,
> you find there is a contradiction, since there is only allowed to be one
> associated graph, but in this case there are two different ones.

Technical point: even if they are unique graphs, isn't the right conclusion:

    <c> owl:sameAs <d>  .

unless the "{ ... }" is and not a graph itself, but, say, a
representation of a graph, or is it that, they are not equal as
literals, considered as a set of triples with no interpretation.

But if everything is quoted, nothing is ever equal.  Workable, but a
completely different architecture from the ground up - it's like having
only reified statements.

	Andy
Received on Monday, 2 April 2012 20:46:52 UTC

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