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RE: [dcat] rdf graphs and documents

From: Cory Casanave <cory-c@modeldriven.com>
Date: Fri, 30 Apr 2010 06:55:44 -0400
Message-ID: <4F65F8D37DEBFC459F5A7228E5052044A03E76@DATCENTRALSRV.datcentral.local>
To: "Chris Beer" <chris@e-beer.net.au>, "Erik Wilde" <dret@berkeley.edu>
Cc: "William Waites" <ww-keyword-okfn.193365@styx.org>, <public-egov-ig@w3.org>, "Richard Cyganiak" <richard@cyganiak.de>
Chris,
Note that in SPARQL you can have a GRAPH element so that you may
understand the graph that sourced a particular triple to the return
results of a query.  You may also specify the names of graphs to query.

Most if not all "triple stores" are actually quad stores thus allowing
one repository to manage multiple named graphs.

So there is some support, through SPARQL, for the 4th element already.
The RDF-2 argument is that this should be made part of the fundamental
RDF data model, which makes sense to me.

-Cory Casanave

-----Original Message-----
From: Chris Beer [mailto:chris@e-beer.net.au] 
Sent: Friday, April 30, 2010 1:46 AM
To: Erik Wilde
Cc: William Waites; Cory Casanave; public-egov-ig@w3.org; Richard
Cyganiak
Subject: Re: [dcat] rdf graphs and documents

I seriously ( unless my RDF understanding is flawed ) would of assumed  
that you cannot by definition have a rdf:graph element. The graph has  
to be by nature dynamic, that is, it is, graph can only exist when  
subject, predicate, and object are known. It could act as a container  
for the 3 rdf elements, but in and of itself I see no point in  
defining it. I guess what I'm saying, by example, that there is no use  
in trying to define x in algebra, as x could be anything, or more  
importantly, x by itself could be anything. Or to put it another way -  
is there any point in defining a "page containing any combination of  
elements" within HTML - the concept of a page is the end result of  
markup, just as a graph is the end result of any rdf markup. (then  
again, prehaps it is worth defining graph as a rdf doctype or  
something). I'm no expert, so be gentle if I'm completely on the wrong  
track here :)

Cheers

Chris

Sent from my iPhone

On 30/04/2010, at 10:19, Erik Wilde <dret@berkeley.edu> wrote:

> hello.
>
>> We have rdf:subject, rdf:predicate, rdf:object but
>> there is no such thing as rdf:graph to mention the fourth element.  
>> I've
>> invented an equivalent, but does anyone know if there is such a
>> predicate defined anywhere? Is it worth attempting to suggest an  
>> update
>> to the core rdf vocabulary to have this added (also with a  
>> commensurate
>> rdf:Graph class)?
>> We are lacking in tools for talking about graphs in rdf itself it  
>> seems...
>
> i think this is the grand debate about RDF2 and whether named graphs  
> should become part of RDF itself. thanks for your thoughtful email,  
> you described it much better than i was able to do it. the point is  
> that RDF triples in the current RDF world have no coherence, you  
> might find them in various "documents" at various URIs, or all in  
> the same triple store; semantically, there is no difference. for  
> metamodels with a "document" level, there is coherence, and it  
> matters in which document you find a substructure of some data. this  
> is what i wanted to say by saying that "RDF has no documents", but  
> you explained it in a much better way. thanks!
>
> cheers,
>
> dret.
>
Received on Friday, 30 April 2010 10:56:08 GMT

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