Consensus Call Tranche 8 Results

[John C Klensin]

Vint,

I'm trying to wrap up versions of Rationale and Protocol, plus a
small revision to Defs, to reflect what I can about the
consensus call results.  I'll post a note about what has and has
not been done when I post the draft, but two observation, below,
on the Tranche 8 call.

--On Sunday, 19 October, 2008 11:02 -0400 Vint Cerf
<vint at google.com> wrote:

> accept or interest in the following:
> 
> 1. Allow esszet (can be excluded by registry)

> 2. map final sigma into lower case sigma per IDNA2003 (if
> mapping can be done as an exception rule in IDNA2008???)

An important principle of the IDNA2008 model, on which I think
we have consensus (at least among those who see IDNA2008 as at
all useful), is that U-labels and A-labels be able to be
transformed back and forth without any loss of information (or
need to supply external information).  

Mapping Final Sigma into Lower-case Sigma would break the
isomorphism of that relationship because, while Final Sigma
could appear in a U-label, it could not be produced by a
transformation from an A-label back to a U-label.  That is
obviously not a matter for an exception case in either Protocol
or Tables.

I note that the underlying problem with the case-folding
transformation is much more general than the particular case of
Final Sigma.  For example, because of differences in conventions
about the representation of diacritical characters on upper-case
characters, "A" does not map uniquely into "a" but might have
been produced by taking the upper case of á (U+00E1) and
applying orthographic rules that apply for some uses of the
Latin script and not others.

The choices are, therefore,

	(i) Prohibit Final Sigma, just as, e.g., "A" and
	Upper-case Sigma are prohibited.
	
	(ii) Permit Final Sigma as an ordinary character, with
	no mapping, and leave its handling (permit or not,
	variant or sunrise techniques or not) up to the relevant
	registry/zone.
	
	(iii) Fundamentally change the IDNA2008 model.

I do believe that, whatever decisions are made about Final
Sigma, Eszett, or others, that the third option is desirable.

   john