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Re: URI ref comparison - clarification requested

From: Graham Klyne <GK@ninebynine.org>
Date: Mon, 30 Aug 2004 17:32:53 +0100
Message-Id: <>
To: Danny Ayers <danny.ayers@gmail.com>, uri@w3.org

At 21:56 26/08/04 +0200, Danny Ayers wrote:

>There appears (to me at least) to be some conflict between the
>definition of URI references in RFC 2396bis (sec 4.1) and that in RDF
>Concepts [1]. The latter says:
>"Two RDF URI references are equal if and only if they compare as
>equal, character by character, as Unicode strings.".
>I assume the 'ladder' of comparisons in 2396 applies to the URI
>references defined there.
>Is this a simple naming clash (URIrefs != RDFURIrefs) and/or is this
>an issue that should be raised on the RDF lists, or am I missing
>something obvious?

The definitions in RDF Concepts are intended for testing equivalence of 
graphs expressed as RDF abstract syntax.  In particular, it says nothing 
about whether or not two RDF URIrefs denote the same thing (semantically).

The "ladder" in  RFC2396bis is, IIRC, explicitly application dependent, and 
is not a universal definition of URI equivelence.

As far as I'm aware, the RDF Concepts definition is entirely consistent 
with RFC2396bis, and is appropriate for the purposes of RDF, but should not 
be taken to apply to non-RDF data.

>It's another question spawned by the dread Atom project (it could do
>with a normative definition of char-by-char-comparable URI
>serializations), sorry and all that.

I think Atom might reference the ladder in RFC2396bis (which starts with 
character-by-character equivalence), and state explicitly which rung (or 
rungs) of the ladder is (are) appropriate for the purposes of Atom.


Graham Klyne
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Received on Wednesday, 1 September 2004 12:17:08 UTC

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