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Re: New Proposal (6.1) for GRAPHS

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 04 Apr 2012 14:10:36 +0100
Message-ID: <4F7C484C.4050003@epimorphics.com>
To: public-rdf-wg@w3.org


On 04/04/12 13:34, Sandro Hawke wrote:
> On Wed, 2012-04-04 at 08:25 +0100, Andy Seaborne wrote:
>>
>> On 03/04/12 01:27, Sandro Hawke wrote:
>>>>> 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"?
>>> My intuition is that there are important thing you can't do if you allow
>>> more than one graph to be associated with the named object, but I
>>> haven't really explored that because SPARQL datasets clearly allow only
>>> one GRAPH for a given name, so I figured we'd stick with that.  That's
>>> why I said hasGraph was a functional property.
>>
>> A query executes at some (idealized) point in time, and a query closes
>> the world to execute (or they'd never complete!).   An RDF Dataset is
>> the local concept for the data being queried - there's no statement
>> about anything outside the local context made, or needed for SPARQL.
>
> I know all that, but I can't figure out what that has to do with whether
> hasGraph is a functional property.

It's whether the graph is partial or complete-and-closed.  Lee's example 
bring that out; it's also in the earlier "what a TriG doc merge?"

Doc 1:
<u> { <a> <b> <c> }

Doc 2:
<u> { <x> <y> <z> }

-> merge ->

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

You say rdf:hasGraph is functional -- what is the scope of that?

Is it the TriG doc or is it the web?

>               * Zero or more named graphs. Each named graph is a pair
>                 consisting of an IRI (the graph name), and an RDF graph.
>                 Graph names are unique within an RDF dataset.


> Since "Graph names are unique within an RDF dataset", R is a function
> (or, in OWL speak: R is functional).

All SPARQL says is graph names are unique within an RDF dataset, not on 
the web.  Functional in the mapping name -> graph in the dataset.

It makes no statement outside the dataset.

But a functional OWL property is functional not just in the  graph in 
which it's used.

G1
<a> <functional> <b> .
G2
<a> <functional> <c> .

merge
<a> <functional> <b> , <c> .

and conclude

   <b> owl:sameAs <c>

	Andy
Received on Wednesday, 4 April 2012 13:11:08 UTC

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