Re: Unicode, Cure-all or Kill-all?

From: Martin J Duerst (
Date: Wed Aug 14 1996 - 06:35:46 EDT

John Jenkins wrote:

>The model followed by the IRG -- based ultimately on Japanese standards
>practice -- makes a three-fold distinction.
>X-variants: Different semantics, different abstract shape
>Y-variants: Same semantics, different abstract shape
>Z-variants: Same semantics, same abstract shape but different actual

Given the examples and explanations in the Unicode standard,
and the example of C"machine"/J"table", this should be different:

X-axis: Different semantics (shape is irrelevant)
Y-axis: Different abstract shape (semantics is irrelevant)
Z-axis: Different actual shape (semantics is irrelevant)

John's explanation looks as if everything can be represented
as a tree, with X-variants (semantics) sorted out at the first
level, Y-variants (abstract shape) sorted out at the second
level, and Z-variants (actual shape) sorted out at the
third level. This is (mostly) true for Y and Z axes (it would be
extremely far-fetched to construct examples with different
abstract shape, but the same actual shape, although with
some exotic fancy fonts, that might be done). It is however
not true for the X axis vs. the Y/Z axes. Examples of Tai2
have different X axis values depending on whether they
mean "Taiwan", "Typhoon", or "Sir", but they have the same
Y value, and the same Z value if they come from the same font.

For codepoint identification, only the Y axis is relevant.
The X axis (semantics) is sometimes consulted to decide
whether shape differences have to be classified as Y (abstract)
or Z (actual), because in some cases, a small shape difference
can make a completely different character. Example having
identical shape (Y/Z), however, are given a single codepoint
irrespective of X value.

>"A" and "B" are examples of X-variants.
As are "porportional to", "difference between", "similar to",
"APL tilde", "cycle", "not", and "tilde operator, and all the
different hyphens.

>A grotesque "a" and gothic "a" are examples of Y-variants.
"\" and "-" for set difference would be another example.
The shapes can in some cases really look totally different,
without any clue that it is the same if you don't know
what it means.

>A Geneva "a" and Helvetica "a" are examples of Z-variants.

Regards, Martin.

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