Subject: Big5 and CNS-11643 are almost the same

From: Stephen G Simpson <[email-masked]>
Date: Fri, 28 May 1993 15:58:05 -0400

As we all know, Big5 is a 2-byte Chinese character coding scheme that
is extremely popular in Taiwan.  As Dr. Farn has said, it the most
popular coding scheme for both PCs and Macs, and it is supported by
virtually all software.

Less well known but also important is CNS-11643, a 2-byte Chinese
character coding scheme which is endorsed as the national standard by
the ROC government.  Dr. Farn has said that support for CNS-11643 is
required in software procured for government use.

Recently CCNET has seen some discussion of the relationship between
Big5 and CNS-11643.  I asserted that these two coding schemes are the
same.  Others asserted that they are totally different.

Now I have done a little further research on this matter.  In an old
discussion of an early version of the Unicode cross reference table
cjkxref.fix, the following column header information appears:

> 3. BIG-5: 4 hexadecimal digits
> 4. CNS 11643-1986: L-XXXX (4 hexadecimal digits), where L is one of
>       1 = Frequent characters
>       2 = Less frequent characters
>       E = extensions
>    The first two levels are the two levels of BIG-5, minus the two
>    characters C94A and DDFC, rearranged (in the same order) to fit in
>    the range of graphic characters (A1-7E)

(The old discussion is archived at ifcss.org in
~ftp/china-studies/compute/ccnet-archive/chcoding.  The current
version of cjkxref.fix is available at unicode.org in
~ftp/pub/MappingTables.)

The above information appears to be confirmed by an examination of
columns 3 and 4 of cjkxref.fix.  Although the Big5 and CNS-11643
coding schemes are not identical, there appears to be a very simple
one-to-one correspondence between them.  With a very small number of
exceptions, they appear to contain exactly the same characters in
exactly the same order.

Unfortunately, I do not have access to any official standards document
in which the relationship between Big5 and CNS-11643 is spelled out.
Perhaps someone who is involved with ROC goverment software
acquisition and standards can supply this kind of official
information?

In any case, it does appear that, for practical purposes, Big5 and
CNS-11643 are the same.  Thus I think it is fair to say that Big5 is
not only extremely popular in Taiwan, it is also very close to being
an officially approved ROC government standard.  The practical
importance of this is that, if you are developing software for use in
Taiwan, Big5 is the one Chinese character coding scheme that you will
have to support.

Stephen G. Simpson
Department of Mathematics, Pennsylvania State University
333 McAllister Building, University Park, State College, PA 16802
Office phone: +1 814 863-0775      Internet: [email-masked]
Home phone: +1 814 238-2274        Bitnet: T20 AT PSUVM
FAX: +1 814 865-3735