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Re: Labelled graphs

From: Ivan Herman <ivan@w3.org>
Date: Mon, 30 Apr 2012 10:31:11 +0200
Cc: public-rdf-wg@w3.org
Message-Id: <67D56688-5CAE-4FD5-A075-068534DE2C19@w3.org>
To: Andy Seaborne <andy.seaborne@epimorphics.com>

On Apr 30, 2012, at 10:02 , Andy Seaborne wrote:

> 
> 
> On 30/04/12 08:38, Ivan Herman wrote:
>> 
>> On Apr 30, 2012, at 09:24 , Pat Hayes wrote: [snip]
>> 
>>> 
>>>> 
>>>> 
>>>> I must admit I am not sure what
>>>> http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1#Blank_Nodes
>>>> (ie, that blank nodes have a file scope) mean eg, in terms of
>>>> semantics. If I look at the more abstract level
>>>> 
>>>> (D, (<u>,G), (<v>,H))
>>>> 
>>>> with G and H being different graphs, what does it mean that they
>>>> share a blank node?
>>> 
>>> Exactly what it says. There is nothing in the 2004 RDF specs that
>>> prevents two different and distinct graphs from sharing a blank
>>> node. (As to whether there SHOULD have been something preventing
>>> this, maybe so: but in fact, there isn't.)
>>> 
>> 
>> I am surprised but I of course believe you:-)
>> 
>> However... Are we sure that existing systems (RDFLib, Jena,
>> you-name-it) are prepared for this? Many of those have some sort of a
>> named graph/quad store implemented already, possibly with TriG input,
>> and it would be good to know whether this would force them to
>> re-engineer their blank node processing workflow...
>> 
>> Ivan
> 
> Jena has no problem with bNodes shared between graphs.
> 
> It happens - a inference graph and it's base graph share bNodes in the base graph. (For RDFS, the base graph is a subgraph of the inference graph.)
> 
> In Jena, blank nodes have a system-wide internal id, and are not identified relative to the graph they are in.  The identifier is global, it is not a IRI (two different spaces of names).  The identifier is not related to the label used in the syntax file.

Ok. AFAIK, the situation is fairly similar in RDFLib as far as I could see, though the only parser they seem to have at this point is TriX and TriG...

Ivan


> 
> 	Andy
> 


----
Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 30 April 2012 08:28:39 UTC

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