Chapter 3. Important Concepts for Character Coding Systems

12

example, citizen registration system), this is too heavy theme for this document. This is because

there are no standardized or encouraged methods to handle these ACR. You may have to build

the whole system for such purposes. Good luck!

CCS in  the Report  is same as what I wrote in this document. It has concrete examples: ASCII,

ISO 8859 {1,2,. . . ,15}, JISX 0201, JISX 0208, JISX 0212, KSX 1001, KSX 1002, GB 2312, Big5, CNS

11643, TIS 620, VISCII, TCVN 5712, UCS2, UCS4, and so on. Some of them are national standards,

some are international standards, and others are de facto standards.

CEF and CES in  the Report  correspond to CES in this document. This document will not dis 

tinguish these two, since I think there are no inconvenience. An encoding with a significant CEF

doesn't have a significant CES (in  the Report  meaning), and vice versa. Then why should we

have to distinguish these two? The only exception is UTF 16 series. In UTF 16 series, UTF 16 is

a CEF and UTF 16BE is a CES. This is the only case where we need distinction between CEF and

CES.

Now, CES is a concrete concept with concrete examples: ASCII, ISO 8859 {1,2,. . . ,15}, EUC JP,

EUC KR, ISO 2022 JP, ISO 2022 JP 1, ISO 2022 JP 2, ISO 2022 CN, ISO 2022 CN EXT, ISO 2022 

KR, ISO 2022, VISCII, UTF 7, UTF 8, UTF 16LE, UTF 16BE, and so on. Now they are encodings

themselves.

The most important concept in this section is distinction between coded character set and encod 

ing. Coded character set is a component of encoding. Text data are described in encoding, not coded

character set.

3.2 Stateless and Stateful

To construct an encoding with two or more CCS, CES has to supply a method to avoid collision

between these CCS. There are two ways to do that. One is to make all characters in the all CCS

have unique code points. The other is to allow characters from different CCS to have the same

code point and to have a code such as escape sequence to switch SHIFT STATE, that is, to select

one character set.

An encoding with shift states is called STATEFUL and one without shift states is called STATE 

LESS.

Examples of stateful encodings are: ISO 2022 JP, ISO 2022 KR, ISO 2022 INT 1, ISO 2022 INT 2,

and so on.

For example, in ISO 2022 JP, two bytes of

0x24 0x2c

may mean a Japanese Hiragana character

'GA' or two ASCII character of '$' and ',' according to the shift state.