Why doesn't Ideographic (ID) in UAX#14 have half-width katakana?

Martin J. Dürst duerst at it.aoyama.ac.jp
Thu Aug 27 02:39:31 CDT 2015

Sorry to be late. Just some background information.

On 2015/04/28 14:57, Makoto Kato wrote:

> Although I read JIS X 4051, it doesn't define that half-width katakana
> and full-width katakana are differently.

I was on the committee that updated JIS X 4015 (mostly liaison/observer 
role). The chair of that committee was Prof. Shibano (芝野 耕司), who 
was also chair of the committee responsible for the Japanese character 
standards as well as chair of ISO/IEC JTC1 SC2.

I very well remember that he explained at one point that as far as the 
standards were concerned, full-width and half-width versions were 
considered one and the same character. In modern terms, the standards' 
view was that single-byte and double-byte encodings of these characters 
were just different "encoding forms" of one and the same abstract character.

This view is confirmed e.g. by the character names used in the 1997 
version (confirmed 2002) of JIS X 0201, which are just "KATAKANA LETTER 
A",... Anybody interested can dig deeper, JIS X 0201 was just what was 
most easily accessible to me now.

The justification behind this is that they are linguistically not 
different at all, and that they were intended just as a fallback due to 
technology (memory, display resolution) limitations.

In practice, technical restrictions in early limitations (one byte == 
one (half-width) character cell) led to a typographic distinction. The 
fact that half-width Kana used less space was exploited in fixed-pitch 
screen design. That lead to a desire to keep the distinction when 
round-tripping via Unicode, and thus to different character names.

Regards,   Martin.

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