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Proposal for ISSUE-40 Skolemization

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 12 May 2011 12:47:17 +0100
Message-Id: <AE38ABA6-F207-4585-B0FD-A2825BC79563@cyganiak.de>
To: "RDF-WG public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
Below is a complete proposal including intro text and detailed wording about the .well-known mechanism, based on a combination of the original proposal from the wiki, and PatH's comments. It's also on the wiki here:
http://www.w3.org/2011/rdf-wg/wiki/Skolemisation#Updated_Proposal


On 28 Apr 2011, at 06:10, Pat Hayes wrote:
> I would prefer to avoid the "skolem" terminology altogether.

I am fine with avoiding “skolem”. But I believe that *some* term is necessary. First, writing the spec is awkward if one has to repeatedly refer to “an IRI that has been introduced solely to replace a blank node”. Second, I believe that eventually we and others will come to use *some* shorthand term in everyday technical conversation, so why not just bite the bullet and define a term for it in the spec.

I'll stick to “Skolem IRI” for now, until another term has been proposed. I removed mentions of “Skolemization”.

> it really ought to be capitalized, as it is a direct use of the name of Theo Skolem.

Thoralf. I have now capitalized the term.

> It is not clear what is meant by " identifiable by other systems". Identifiable as being skolem URIs? Or in some stronger sense of 'identifiable'? If the former, I suggest the wording "identifiable by other systems as Skolem URIs"

This wording seems fine. I ended up using “recognizable outside of the system boundaries” to avoid “identify” and talking about “systems and other systems”.

The complete proposal is below.

Best,
Richard


PROPOSAL FOR ADDRESSING ISSUE-40

Add the following in RDF Concepts, Section 6.6 Blank Nodes
http://www.w3.org/TR/rdf-concepts/#section-blank-nodes


6.6.1 Replacing blank nodes with IRIs

Blank nodes do not have an intrinsic name in the RDF abstract syntax. In situations where such a name is required, implementations MAY systematically replace blank nodes in an RDF graph with IRIs. Systems wishing to do this SHOULD mint a new, globally unique IRI for each blank node. Such IRIs are known as ''Skolem IRIs''.

Systems may wish to mint Skolem IRIs in such a way that they can recognize the IRIs as having been introduced solely to replace a blank node, and map back to the source blank node where possible.

Systems which want Skolem IRIs to be recognizable outside of the system boundaries SHOULD use a well-known IRI [RFC5785] with the registered name “SteveH”. This is an IRI that uses the HTTP or HTTPS scheme, or another scheme that has been specified to use well-known IRIs; and whose path component starts with /.well-known/SteveH/ .

For example, the authority responsible for the domain “example.com” could mint the following recognizable Skolem IRI:

http://example.com/.well-known/SteveH/d26a2d0e98334696f4ad70a677abc1f6

Note: “SteveH” is a placeholder. Names currently under discussion are “genid”, “bnode”, “skolem”.

Note: RFC 5758 only specifies well-known URIs, not IRIs. For the purpose of this document, a well-known IRI is any IRI that results in a well-known URI after IRI-to-URI mapping [RFC3987].
Received on Thursday, 12 May 2011 11:47:46 GMT

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