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RE: statements about a graph (Named Graphs, reification)

From: Michael Schneider <schneid@fzi.de>
Date: Tue, 4 Sep 2007 15:29:34 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A03745BE@judith.fzi.de>
To: "Richard Cyganiak" <richard@cyganiak.de>
Cc: "K-fe bom" <u9x3n_15so@hotmail.com>, <semantic-web@w3.org>

Hi again, Richard!

>-----Original Message-----
>From: semantic-web-request@w3.org 
>[mailto:semantic-web-request@w3.org] On Behalf Of Richard Cyganiak
>Sent: Tuesday, September 04, 2007 2:02 PM
>To: Michael Schneider
>Cc: K-fe bom; semantic-web@w3.org
>Subject: Re: statements about a graph (Named Graphs, reification)
>
>
>On 4 Sep 2007, at 13:02, Michael Schneider wrote:

>> AFAICS, what you suggest here is just of the form: "Take
>> some URI, and interprete it in a way that it denotes some RDF  
>> graph, and
>> then start to make assertions about this resource in the form of RDF
>> triples."
>
>Yes. That's the one-sentence description of named graphs.
>
>> This happily maps into the current RDF framework and its model
>> theoretic semantics.
>
>No. Using vanilla RDF without semantic extensions, you cannot record  
>the fact that some triple <a> <b> <c> is in some graph <d>. Named  
>graphs is a minimum semantic extension that lets you do this.

Good. By having a dedicated document representing the graph of all triples
of interest, and also having an URI for this document, I am now able to make
assertions about this graph. 

Ok, then let's discuss more practical issues (leaving this subtle RDF
semantics stuff to the academic world). Until now, we had the only usecase
that someone wanted to annotate a complete RDF document, which already exist
somewhere having an URI. This is certainly the easiest case to handle in
practice. But there will probably often be the more demanding situation,
where I want to make assertions about some ad hoc set of RDF triples, which
is not yet published as a special RDF document anywhere. In your previous
post, you already gave a hint how one can handle this situation:

> I put the statements into the document itself, or into an external 
> document, whatever is more convenient.
>
> To process this kind of data, you need an implementation of the RDF  
> Dataset or Named Graph Set, which keeps track of the source of  
> statements. Most RDF toolkits have support for this these days. E.g.,  
> when you load multiple documents into a Jena Model, it won't know  
> which statements are from which document. When you load them into a  
> Dataset (called DataSource in Jena IIRC), then it remembers which  
> statements are in which graph.      

But I have difficulties to understand this. Let's make a case: I have a
graph G. Now I like to annotate any single triple t_i (or singleton subgraph
G_i) in it (e.g. I like to store different provenance information about each
triple). I understand that with NamedGraphs, I can do the following for each
i:

   G_i { t_i } .
   G_i p_1 o_1 . 
       ... 
   G_i p_n o_n .   

But how can I bring this information into the Semantic Web, acutally?
Creating a separate RDF document for each of the G_i hardly seems to be a
practical solution. But I certainly haven't understand the second one of the
above paragraphs?  

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: Michael.Schneider@fzi.de
Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555

FZI Forschungszentrum Informatik an der Universität Karlsruhe
Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
Tel.: +49-721-9654-0, Fax: +49-721-9654-959
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Received on Tuesday, 4 September 2007 13:29:47 UTC

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