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Re: Labelled graphs

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Mon, 30 Apr 2012 09:02:43 +0100
Message-ID: <4F9E4723.4000501@epimorphics.com>
To: public-rdf-wg@w3.org


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.

	Andy
Received on Monday, 30 April 2012 08:03:12 UTC

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