Big5
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Big-5 or Big5 is a character encoding method used in Taiwan (Republic of China) and Hong Kong for Traditional Chinese characters. Its Mainland China equivalent is GB.
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[edit] Organization
The original Big5 character set is sorted first by usage frequency, second by stroke count, lastly by Kangxi radical.
The original Big5 character set lacked many commonly used characters. To solve this problem, each vendor developed its own extension. The ETen extension became part of the current Big5 standard through popularity.
The structure of Big5 does not conform to the ISO 2022 standard, but rather bears a certain similarity to the Shift JIS encoding. It is a double-byte character set (DBCS) with the following structure:
| First byte ("lead byte") | 0x81 to 0xfe |
| Second byte | 0x40 to 0x7e, 0xa1 to 0xfe |
Certain variants of the Big5 character set, for example the HKSCS, uses an expanded range for the lead byte including values in the 0x81 to 0xA0 range (similar to Shift JIS).
If the second byte is not in the correct range, behaviour is undefined (i.e., varies from system to system).
The numerical value of individual Big5 codes are frequently given as a 4-digit hexadecimal number, which describes the two bytes that comprise the Big5 code as if the two bytes were a big endian representation of a 16-bit number. For example, the Big5 code for a full-width space, which are the bytes 0xa1 0x40, is usually written as 0xa140 or just A140.
Strictly speaking, the Big5 encoding contains only DBCS characters. However, in practice, the Big5 codes are always used together with an unspecified, system-dependent single-byte character set (ASCII, or an 8-bit character set such as code page 437), so that you will find a mix of DBCS characters and single-byte characters in Big5-encoded text. Bytes in the range 0x00 to 0x7f that are not part of a double-byte character are assumed to be single-byte characters. (For a more detailed description of this problem, please see the discussion on "The Matching SBCS" below.)
The meaning of non-ASCII single bytes outside the permitted values that are not part of a double-byte character varies from system to system. In old MSDOS-based systems, they are likely to be displayed as 8-bit characters; in modern systems, they are likely to either give unpredictable results or generate an error.
[edit] A more detailed look at the organization
In the original Big5, the encoding is compartmentalized into different zones:
| 0x8140 to 0xa0fe | Reserved for user-defined characters 造字 |
| 0xa140 to 0xa3bf | "Graphical characters" 圖形碼 |
| 0xa3c0 to 0xa3fe | Reserved, "not" for user-defined characters |
| 0xa440 to 0xc67e | Frequently used characters 常用字 |
| 0xc6a1 to 0xc8fe | Reserved for user-defined characters |
| 0xc940 to 0xf9d5 | Less frequently used characters 次常用字 |
| 0xf9d6 to 0xfefe | Reserved for user-defined characters |
The "graphical characters" actually comprise punctuation marks, partial punctuation marks (e.g., half of a dash, half of an ellipsis; see below), dingbats, foreign characters, and other special characters (e.g., presentational "full width" forms, digits for Suzhou numerals, zhuyin fuhao, etc.)
In most vendor extensions, extended characters are placed in the various zones reserved for user-defined characters, each of which are normally regarded as associated with the preceding zone. For example, additional "graphical characters" (e.g., punctuation marks) would be expected to be placed in the 0xa3c0–0xa3fe range, and additional ideograms would be placed in either the 0xc6a1–0xc8fe or the 0xf9d6–0xfefe range. Sometimes, this is not possible due to the large number of extended characters to be added; for example, Cyrillic letters and Japanese kana have been placed in the zone associated with "frequently-used characters".
[edit] What a Big5 code actually encodes
Contrary to popular belief, an individual Big5 code does not always represent a complete semantic unit. The Big5 codes of ideograms are always ideograms, but codes in the "graphical characters" section are not always complete "graphical characters". What Big5 encodes are particular graphical representations of characters or part of characters that happen to fit in the space taken by two monospaced ASCII characters. This is a property of double-byte character sets as normally used in CJK (Chinese, Japanese, and Korean) computing, and is not a unique problem of Big5.
(The above might need some explanation by putting it in historical perspective, as it is theoretically incorrect: Back when text mode personal computing was still the norm, characters were normally represented as single bytes and each character takes one position on the screen. There was therefore a practical reason to insist that double-byte characters must take up two positions on the screen, namely that off-the-shelf, American-made software would then be usable without modification in a DBCS-based system. If a character can take an arbitrary number of screen positions, software which was written with the assumption that one byte of text takes one screen position would produce incorrect output. Of course, if a computer never had to deal with the text screen, the manufacturer would not enforce this artificial restriction; the Apple Macintosh is an example. Nevertheless, the encoding itself must be designed so that it works correctly on text-screen-based systems.)
To illustrate this point, consider the Big5 code 0xa14b (…). To English speakers this looks like an ellipsis and the Unicode standard identifies it as such; however, in Chinese, the ellipsis consists of six dots that fit in the space of two Chinese characters (……), so in fact there is no Big5 code for the Chinese ellipsis, and the Big5 code 0xa14b just represents half of a Chinese ellipsis. It represents only half of an ellipsis because the whole ellipsis should take the space of two Chinese characters, and in many DBCS systems one DBCS character must take exactly the space of one Chinese character.
Characters encoded in Big5 do not always represent things that can be readily used in plain text files; an example is "citation mark" (0xa1ca, ﹋), which is, when used, required to be typeset under the title of literary works. Another example is the Suzhou numerals, which is a form of scientific notation that requires the number to be laid out in a 2-D form consisting of at least two rows.
[edit] The Matching SBCS
In practice, Big5 cannot be used without a matching SBCS; this is mostly to do with a compatibility reason. However, as in the case of other CJK DBCS character sets, the SBCS to use has never been specified. Big5 has always been defined as a DBCS, though when used it must be paired with a suitable, unspecfied SBCS and therefore used as what some people call a MBCS; nevertheless, Big5 by itself, as defined, is strictly a DBCS.
The SBCS to use being unspecified implies that the SBCS used can theoretically vary from system to system. Nowadays, ASCII is the only possible SBCS one would use. However, in old DOS-based systems, Code Page 437—with its extra special symbols in the control code area including position 127—was much more common. Yet, on a Macintosh system with the Chinese Language Kit, or on a Unix system running the cxterm terminal emulator, the SBCS paired with Big5 would not be Code Page 437.
Outside the valid range of Big5, the old DOS-based systems would routinely interpret things according to the SBCS that is paired with Big5 on that system. In such systems, characters 127 to 160, for example, were very likely not avoided because they would produce invalid Big5, but used because they would be valid characters in Code Page 437.
The modern characterization of Big5 as an MBCS consisting of the DBCS of Big5 plus the SBCS of ASCII is therefore historically incorrect and potentially flawed, as the choice of the matching SBCS was, and theoretically still is, quite independent of the flavour of Big5 being used.
[edit] History
The Big5 encoding was defined by the Institute for Information Industry of Taiwan in 1984. According to some accounts, Big5 was popularized by its adoption in several commercial software packages, especially the ET Chinese system which ran on MS-DOS.
The Republic of China government declared it their standard in mid-1980s since Big5 was already the de facto standard by that time.
[edit] Extensions
The original Big-5 only include CJK ideograms from 常用國字標準字體表 and 次常用國字標準字體表, but not letters from people's names, place names, dialects, chemistry, biology, Japanese kana. As a result, many Big-5 supporting software include extensions to address the problems.
[edit] Vendor Extensions
[edit] ETEN extensions
In ETEN Chinese operating system, the following code points are added to make it compliant with IBM5550 code page:
- A3C0-A3E0: 33 control characters.
- C6A1-C875: circle 1-10, bracket 1-10, Roman letters 1-9 (i-ix), CJK radical glyphs, Japanese hiragana, Japanese katakana, Cyrillic characters
- F9D6-F9FE: '碁', '銹', '恒', '裏', '墻', '粧', '嫺', and 34 extra symbols.
In some versions of Eten, there are extra graphical symbols and Simplified Chinese characters.
[edit] Microsoft code pages
Microsoft created its own version of Big5 extension as Code page 950 for use with Microsoft Windows, which supports ETEN's extensions, but only the F9D6-F9FE code points. In Windows ME, the euro currency symbol is mapped to Big-5 code point A3E1, but not in later versions of the operating system.
After installing Microsoft's HKSCS patch on top of traditional Chinese Windows (or any version of Windows 2000 and above with proper language pack), application using code page 950 automatically uses a hidden code page 951 table. The table supports all code points in HKSCS-2001, except for the compatibility code points specified by the standard[1].
[edit] ChinaSea font
ChinaSea fonts are Tranditional Chinese fonts made by ChinaSea. The fonts are rarely sold separately, but are bundled with other products, such as Chinese version of Microsoft Office 97. The fonts support Japanese kana, kokuji, and other characters missing in Big-5. As a result, the ChinaSea extension have become more popular than the government-supported extensions. Some Hong Kong BBS had used encodings in ChinaSea fonts before the introduction of HKSCS.
[edit] 'Sakura' font
The 'Sakura' font (日和字集 Sakura Version) is developed in Hong Kong, designed to be compatible with HKSCS. It adds support of kokuji and proprietary dingbats (including Doraemon) not found in HKSCS.
[edit] Unicode-at-on
Unicode-at-on (Unicode補完計畫), formerly BIG5 Extension, extends BIG-5 by altering code page tables, but uses ChinaSea extension starting with version 2. However, with the bankurptcy of ChinaSea, late development, and the increasing popularity of HKSCS and Unicode (the project is not compatible with HKSCS), the success of this extension is limited at best.
[edit] Official Extensions
[edit] Taiwan Ministry of Education font
Taiwan Ministry of Education supplied its own font for use internally.
[edit] Taiwan Council of Agriculture font
Taiwan's Council of Agriculture font, Executive Yuan introduced a 133-character custom font that include 84 from 'fish' radical, 7 from 'bird' radical.
[edit] Big5+
Chinese Foundation for Digitization Technology introduced Big5+ in 1997, which used over 20000 code points to incorporate all CJK ideograms in Unicode 1.1. However, the extra code points exceeded original Big-5 definition (Big5+ uses high byte values 81-FE, low byte values 40-7E, 80-FE), prevented it from being installed to Microsoft Windows.
[edit] Big-5E
To allow Windows user to use custom fonts, Chinese Foundation for Digitization Technology introduced Big-5E, which included 3954 letters. The system is incompatible with Big5+, removed the Japanese kana from ETEN extension, so it became unpopular.
[edit] Big5-2003
Chinese Foundation for Digitization Technology made a Big5 definition, and put it into CNS 11643 in note form, making it part of the official standard in Taiwan.
Big5-2003 incorporates all Big-5 character introduced in 1984 ETEN extensions (code points A3C0-A3E0, C6A1-C7F2, F9D6-F9FE), Euro symbol. Cyrillic characters were not included because the authority claimed CNS 11643 do not include such characters.
[edit] HKSCS
Hong Kong also adopted Big5 for character encoding. However, Cantonese uses many archaic and some colloquial Chinese characters that were not available in the normal Big5 character set. To solve this problem, the Hong Kong Government created the Big5 extensions Government Chinese Character Set in 1995 and Hong Kong Supplementary Character Set in 1999. The Hong Kong extensions were commonly distributed as a patch. It is still being distributed as a patch by Microsoft, but a full Unicode font is also available from the Hong Kong Government’s web site.
HKSCS include all the characters from the common ETEN extension, plus some letters from Simplified Chinese, place names, people's names, Cantonese phrases (including profanity).
[edit] See also
[edit] References
- Lunde, Ken (1999). CJKV Information Processing, First Edition, O'Reilly and Associates, Inc.. ISBN 1-56592-224-7.
[edit] External links
- Chinese character codes: an update by Christian Wittern
- CNS 11643 official web site has information about the Big5e character set (an extended version of Big5) in the "Chinese Information Code" section
- Hong Kong Supplementary Character Set Info
- Microsoft's Windows Codepage 950 (Traditional Chinese Big5)
- Graphical View of Big5 in ICU's Converter Explorer
- Big5 introduction Contains differences between extensions.
