UCA unnecessary collation weight 0000

[Richard Wordingham via Unicode]

On Fri, 2 Nov 2018 14:27:37 -0700
Ken Whistler via Unicode <unicode at unicode.org> wrote:

> On 11/2/2018 10:02 AM, Philippe Verdy via Unicode wrote:

> > UTR#10 still does not explicitly state that its use of "0000" does
> > not mean it is a valid "weight", it's a notation only  
> 
> No, it is explicitly a valid weight. And it is explicitly and 
> normatively referred to in the specification of the algorithm. See 
> UTS10-D8 (and subsequent definitions), which explicitly depend on a 
> definition of "A collation weight whose value is zero." The entire 
> statement of what are primary, secondary, tertiary, etc. collation 
> elements depends on that definition. And see the tables in Section
> 3.2, which also depend on those definitions.

The definition is defective in that it doesn't handle 'large weight
values' well.  There is the anomaly that a mapping of collating element
to [1234.0000.0000][0200.020.002] may be compatible with WF1, but the
exactly equivalent mapping to [1234.020.002][0200.0000.0000] makes the
table ill-formed.  The fractional weight definitions for UCA eliminate
this '0000' notion quite well, and I once expected the UCA to move to
the CLDRCA (CLDR Collation Algorithm) fractional weight definition.
The definition of the CLDRCA does a much better job of explaining
'large weight values'.  It turns them from something exceptional to a
normal part of its functioning.  

> > (but the notation is used for TWO distinct purposes: one is for 
> > presenting the notation format used in the DUCET  
> 
> It is *not* just a notation format used in the DUCET -- it is part of 
> the normative definitional structure of the algorithm, which then 
> percolates down into further definitions and rules and the steps of
> the algorithm.

It's not needed for the CLDRCA!  The statement of the UCA algorithm
does depend on its notation, but it can be recast to avoid these zero
weights.

Richard.