Chapter 3. Important Concepts for Character Coding Systems

11

code can call encoding and can call coded character set. Thus this word can be used only in the case

when both of them can be regard in the same category. This word should be avoided in serious

discussions. This document will not use this word hereafter.

Codeset is a word to call encoding or character encoding scheme.

1

charset is also a well used word. This word is used very widely, for example, in MIME (like

Content Type:

text/plain, charset=iso8859 1

), in XLFD (X Logical Font Descrip 

tion) font name (CharSetResigtry and CharSetEncoding fields), and so on. Note that charset in

MIME is encoding, while charset in XLFD font name is coded character set. This is very confusing.

In this document, charset and character set are used in XLFD meaning, since I think character set

should mean a set of characters, not encoding.

Ken Lunde's  CJKV Information Processing  uses a word encoding method. He says that ISO 

2022, EUC, Big5, and Shift JIS are examples of encoding methods. It seems that his encoding method

is CES in this document. However, we should notice that Big5 and Shift JIS are encodings while

ISO 2022 and EUC are not.

2

Character Encoding Model, Unicode Technical Report #17 (

http://www.unicode.org/unicode/

reports/tr17/

) (hereafter,  the Report ) suggests five level model.

  ACR: abstract character repertoire

  CCS: Coded Character Set

  CEF: Character Encoding Form

  CES: Character Encoding Scheme

  TES: Transfer Encoding Syntax

TES is also suggested in RFC 2130 (

http://www.faqs.org/rfcs/rfc2130.html

). Some ex 

amples of TES are: base64, uuencode, BinHex, quoted printable, gzip, and so on. TES means a trans 

form of encoded data which may (or may not) include textual data. Thus, TES is not a part of

character encoding. However, TES is important in the Internet data exchange.

When using a computer, we rarely have a chance to face with ACR. Though it is true that CJK

people have their national standard of ACR (for example, standard for ideograms which can be

used for personal names) and some of us may need to handle these ACR with computers (for

1

This document used a word codeset before Novermber 2000 to call encoding. I changed terminology since I could

not find a word codeset in documents written in English (I adopted this word from a book in Japanese). encoding seems

more popular.

2

During I18N programming, we will frequently meet with EUC JP or EUC KR, while we well rarely meet with

EUC. I think it is not appropriate to stress EUC, a class of encodings, over EUC JP, EUC KR, and so on, concrete

encodings. It is just like regarding ISO 8859 as a concrete encoding, though ISO 8859 is a class of encodings of ISO

8859 {1,2,. . . ,15}.