Subject: Analysis on Pure GuoBiao Based Schemes

From: Rupert Zhu <[email-masked]>
Date: Tue, 12 Feb 91 23:07:15 EST

Analysis on Pure GuoBiao Based Schemes
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This is a short introductory article.  The experts please skip it.  :-)

Pure GuoBiao is designed to record any Chinese character using a pair
of bytes, each byte being a printable ASCII character (namely, ASCII
characters 33--126).  In theory, this enables the direct transmission
of Chinese text through E-mail (without any encoding).

In pure GuoBiao case, both Chinese text and English text share
the ordinary (7-bit) ASCII characters.  There is a need to distinguish
the English text from Chinese text.  Two solutions have been proposed,
namely, the zW scheme and the HZ scheme.  They both use some special
"escape" symbols to separate the two types of texts.  To ensure safe
transmission, these escape symbols should be printable characters
as well.

zW scheme uses the pair "zW" to be the separator, while the HZ scheme
uses "~{" and "~}" to indicate the start and end of Chinese text.
The symbols adopted by HZ scheme look more meaningful since the
character '~' is a conventional escape character in some well
established systems (like UNIX mail system).  But it risks higher
chance of being misunderstood by some computer systems.  In this
regards, the symbol "zW" is much safer.

Is there any room that one can improve the existing schemes?  The
answer is: YES.  Let's partion the set of all possible combinations
of printable ASCII characters into 94 subclasses, according to the
first byte of each pair.  The pure GuoBiao coding used 79 out of these
94 subclasses (or zones), leaving 15 subclasses unused.  In other words,
94 * 79 == 7426  printable pairs were used by GuoBiao coding.  There
are still 94 * 15 == 1410  printable pairs free for other usage.
(I am posting these 1410 free pairs in a separate message.)

The separators used by zW scheme and HZ scheme were chosen from these
1410 free 2-byte pairs.  In theory, any of these free pairs can serve
as a separator, not only "zW", "~{" and "~}".  But in practice, we
have two criteria:
  (1) The separators should be as meaningful as possible.
  (2) The chance of collision with conventional usages should be
      minimized.

The zW scheme is not perfect in criterion (1), while the HZ
scheme is not perfect with respect to criterion (2).

I am not proposing a new scheme or new approach.  I just try to write
down what I have learned, and make it easier for new comers.  Actually,
I very much appreciate the pioneer work by the developers of zW and HZ
schemes.

-- Rupert Zhu
   Dept of C. & O
   University of Waterloo
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