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Re: B-scopes

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Sun, 18 Nov 2012 17:29:38 +0000
Message-ID: <50A91B02.10509@epimorphics.com>
To: public-rdf-wg@w3.org
An RDF graph is copied into a scope by systematically replacing the 
graph's blank nodes with fresh ones in the target scope. If none of the 
source's blank node identifiers are used in the target scope, this can 
be achieved by simply re-using the same blank node identifiers in the 
new scope.

Need to explain "systematically" (which I failed to do without using the 
work "isomorphic".)

The merge of two RDF graphs is the result of copying both graphs into a 
target scope. This ensures that the graphs do not share blank nodes.

I can't follow "this ensures the graphs..."

This ensures that in the merged graph, blank nodes from the input graphs 
are different.

although saying something like converting the two graphs to new ones 
that do not share bNodes then doing a copy (union) seems cleaner.


On 16/11/12 19:10, Richard Cyganiak wrote:
> Hi Alex,
> On 16 Nov 2012, at 16:28, Alex Hall wrote:
>>> [[
>>> A *blank node identifier* is a Unicode string that is not an IRI.
>> Minor nit-pick: An IRI is just a Unicode string that follows a certain format. A blank-node identifier string could be a valid IRI (modulo the syntax rules for bnode labels in the serialization language) in the same sense that a literal string could also be a valid IRI. We just choose to treat blank node labels and IRIs as distinct types of things.
> Fair point. I added the restriction as I hoped to remove a possible source of confusion, but perhaps there are better way of doing this.
> Condensed proposal:
> [[
> A *blank node* is a *blank node identifier*, being a Unicode string, in a scope.
> Every RDF document forms its own, self-contained *scope* for blank nodes. The handling of scopes outside of RDF documents (for example, in RDF stores) is implementation-dependent. Other specifications MAY impose additional scoping rules.
> ]]
> The whole thing, with some additional changes, is here:
> http://www.w3.org/2011/rdf-wg/wiki/User:Rcygania2/B-Scopes#3.4_Blank_Nodes
> I've done a few more changes in an attempt to address Andy's concerns. I try to make clearer there *may* be clashes between blank node identifiers because they don't *have* to be unique, and in that case blank nodes need to be relabelled.
> Best,
> Richard
Received on Sunday, 18 November 2012 17:30:07 UTC

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