Subject: Feature value representations

From: Graham Klyne <[email-masked]>
Date: Wed, 30 Sep 1998 14:34:34 +0100

At 10:25 29/09/98 PDT, Larry Masinter wrote:
[...]
>I've always assumed 'rational' meant 'expressed as a ratio' and suggest
>that the registry draft be updated to make that determination. Even if you'd
>prefer decimals, 256/100 == 2.56 easily enough.

I think this raises a slightly broader issue:  that maybe there should
somewhere be a formal grammar (ABNF) describing the syntax of feature
values.  Currently my -syntax- draft refers to the -reg- draft for feature
value syntax, but maybe the specific value syntax should be defined
together with the combining syntax?

Then, there is the specific issue of how to represent rational numbers.  If
I recall correctly, the term 'rational' was used because 'floating point'
was felt to be inappropriate -- too implementation specific.  Maybe the
term 'real' would be better?

As for notation:  I think that the ratio-of-integers notation Larry has
used is appropriate if one wishes to retain an ability to represent
arbitrary precision values exactly (i.e. without approximation).  I think
that decimal notation is appropriate if it is acceptable that there may be
some level of approximation in representing some values (even if that level
is very small).

So what is the *requirement* here?

If for exact representation whenever possible then I suggest the 'n/m'
notation is used.

If for a convenient and familiar notation with some approximation allowed,
then I think decimal 'ddd.ddd' (without explicit limit on the number of
fractional digits) is OK.

#g

------------
Graham Klyne
([email-masked])