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[Concepts] Editorial changes to Blank Nodes (ISSUE-107)

From: Richard Cyganiak <richard@cyganiak.de>
Date: Fri, 9 Nov 2012 15:49:41 +0000
Message-Id: <4130D1D3-6C8A-47A6-AC01-D157878E59A8@cyganiak.de>
To: RDF Working Group WG <public-rdf-wg@w3.org>
RDF Concepts has a pretty much re-written section on Blank Nodes:

For reference, here's what Concepts says informatively about blank nodes in the Introduction (I didn't change anything there):

Unlike IRIs and literals, blank nodes do not denote specific resources. Statements involving blank nodes say that something with the given relationships exists, without explicitly naming it.

Then here's the new normative text:

The *blank nodes* in an RDF graph are drawn from some arbitrary infinite 
set that fulfils the following conditions:

• It is disjoint from the set of IRIs and the set of all literals.
• Equality within the set is well-defined (*blank node equality*).

Allocating a *fresh blank node* is the action of drawing a new node from the set.

For comparison, this was the old text:

The blank nodes in an RDF graph are drawn from an infinite set. This set is disjoint from the set of all IRIs and the set of all literals. Otherwise, this set of blank nodes is arbitrary.

Given two blank nodes, it is possible to determine whether or not they are the same. Besides that, RDF makes no reference to any internal structure of blank nodes.

The normative text is followed by an informative note:

*Blank node identifiers* are local identifiers that are used in some concrete RDF syntaxes or RDF store implementations. They are always locally scoped to the file or RDF store, and are not persistent or portable identifiers for blank nodes. Blank node identifiers are not part of the RDF abstract syntax, but are entirely dependent on the concrete syntax or implementation. The syntactic restrictions on blank node identifiers, if any, therefore also depend on the concrete RDF syntax or implementation.

I have now added some more sentences:

Since RDF systems generally refer to blank nodes only via such local identifiers, it is necessary to “standardize apart” the blank node identifiers when incorporating data that originates from an external source. This may be done by systematically replacing the blank node identifiers in incoming data with freshly allocated blank node identifiers.

I believe this resolves ISSUE-107, hence I'm marking it PENDINGREVIEW.

Received on Friday, 9 November 2012 15:50:11 UTC

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