W3C home > Mailing lists > Public > semantic-web@w3.org > September 2007

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

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Tue, 4 Sep 2007 17:50:55 +0100
Message-Id: <E096448B-8598-450D-9908-C3F3CDE2D130@cs.man.ac.uk>
Cc: Michael Schneider <schneid@fzi.de>, "K-fe bom" <u9x3n_15so@hotmail.com>, <semantic-web@w3.org>
To: Richard Cyganiak <richard@cyganiak.de>

On 4 Sep 2007, at 17:30, Richard Cyganiak wrote:

> Michael,
>
> On 4 Sep 2007, at 15:29, Michael Schneider wrote:
>> 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,

Sorry to be jumping in, but do you mean "in this thread"? Because  
other use cases are prevalent.

>> which already exist
>> somewhere having an URI. This is certainly the easiest case to  
>> handle in
>> practice.
>
> Yes. I think it's also by far the most common case.

I think almost certainly not. Consider EARL:
	http://www.w3.org/TR/EARL10-Schema/

Or annotation axioms in OWL 1.1.

Or Swoop Change Sets (which do chunk out, so they are a little  
different).

>> 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.
>
> To be honest, I'm not sure that this case occurs *that* much in  
> practice.

Quite often (or will). I want to record when an axiom in my owl  
ontology has been last modified. Do I have extract that axiom and  
publish it in a separate document?

> Triples tend to exist in chunks, and the chunks are usually  
> meaningful in the domain of discourse, and thus make natural units  
> of publication.

Even if isolatable (which is what I presume you meant by "meaningful  
in the domain of discourse), it can be really painful to separate  
them out, and similarly painful to have to name them.

> But then I'm not involved with the advanced research stuff

I trust you agree that putting simple metadata on statements (e.g.,  
provenance) isn't advanced research stuff! At least, it *shouldn't*  
be :)

> where I can imagine this to be very important: attaching  
> uncertainty values to statements, describing inference proof  
> chains, recording differences between RDF graphs and so on. So we  
> will probably need more sophisticated mechanisms at *some* point in  
> the future.

[snip]
>> 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?
>
> You mean publishing or exchanging such annotations? Well, you could  
> serialize them as TriG or TriX documents, or offer a SPARQL  
> endpoint, but I think that neither plain RDF nor named graphs/ 
> SPARQL nor reification are truly well-suited to this use case.
[snip]

Ok, we agree at least that far. Sorry to butt in.

Cheers,
Bijan.
Received on Tuesday, 4 September 2007 16:49:55 UTC

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