Re: [namedgraphs] SPARQL over named graphs with blank nodes

[Olaf H. <ha...@in...>]

Hey,

On Sunday 20 June 2010 08:56:42 Blom, J.J.C. (Jaap) wrote:
> Hi,
> 
> Wel for a number of reasons:
> A) It reads a little easier to track a blank node with a readable label in
>  respect to a UID.

But only for debugging purposes. Right? I mean, this data is meant to be 
processed automatically and an application doesn't care about labels.

>  B) Data received from sources not using NG4J/Jena (and
>  thus not supporting this "rule" of uniquely naming blank nodes)

I don't see a problem here. If you import such data into a Jena Model (or 
Graph) then Jena automatically creates unique blank node identifiers.

>  C) Because
>  I should be able to do it. The RDF defenitions specify that two blank
>  nodes with the same label in different graphs should not be considered the
>  same node on that fact alone. (Sorry if I seem to be ranting here)

Okay.

> Like I said I doubt this is a bug from NG4J (I think it is Jena in this
>  case), but since there are some elements from NG4J involved I need to be
>  sure of this.

Yes, I think it is a problem in Jena. NG4J uses the Jena implementation of 
triple pattern matching over a union of RDF graphs which is implemented
in the 'MultiUnion' class (package 'com.hp.hpl.jena.graph.compose'); more 
precisely, the method 'multiGraphFind'

Greetings,
Olaf