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Re: Proposal for ISSUE-40 Skolemization

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 18 May 2011 20:09:05 +0100
Cc: <public-rdf-wg@w3.org>
Message-Id: <952815F2-1B12-45A8-A29C-1E4E15E3FD3A@cyganiak.de>
To: Peter Frederick Patel-Schneider <pfps@research.bell-labs.com>
Peter,

On 18 May 2011, at 17:19, Peter Frederick Patel-Schneider wrote:
> 3.2 URI-based Vocabulary and Node Identification

All changes fine with me as proposed.

> [[ADD:
> 6.6.1 Replacing blank nodes with IRIs
> 
> Particular IRIs and literals occuring in RDF graphs can each be easily
> identified in both the RDF abstract syntax and in RDF concrete syntaxes.
> However, a particular blank node occuring in an RDF graph cannot be so
> identified,

1. I'd prefer not to mention literals here, as it's about replacing blank nodes with IRIs.

2. This says “IRIs can be easily identified”, which is a bit tautological.

Perhaps a different approach:

[[ADD: Blank nodes do not have identifiers in the RDF abstract syntax. The blank node identifiers introduced by some concrete syntaxes have only local scope and are purely an artifact of the serialization. In situations where stronger identification is needed, …]]

> … systems MAY systematically transform some or all of the blank nodes in an RDF graph into IRIs.  Systems wishing to do this SHOULD mint a new, globally unique IRI (a Skolem IRI) for each blank node so transformed.


Ok

> Implementors should realize that this transformation changes the meaning
> of an RDF graph (but this change is generally not harmful).

That sounds a bit scary. Perhaps:

[[ADD: This transformation does not change the meaning of an RDF graph, except “using up” the Skolem IRI.]]

or perhaps best not mention it at all. It's hard to explain what exactly the “possible harm” would be ...

Best,
Richard




> 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 that 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 Wednesday, 18 May 2011 19:09:53 GMT

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