Традициялық қытай әріптерін кодтау: Big5 жүйесі

Encoding for Traditional Chinese characters

Big 5 or Big5 (t=大五碼) is a Chinese character encoding method used in Taiwan, Hong Kong, and Macau for traditional Chinese characters. The People's Republic of China (PRC), which uses simplified Chinese characters, uses the GB 18030 character set instead. Big5 gets its name from the consortium of five companies in Taiwan that developed it.

Big5 has encoded two duplicate characters: "兀" on 0xA461 (U+5140) and 0xC94A (U+FA0C), "嗀" on 0xDCD1 (U+55C0) and 0xDDFC (U+FA0D). Some encoding mapping also maps the three Suzhou numerals, "〸", "〹" and "〺", in the graphical section to ideograph characters (U+5341, U+5344 and U+5345 respectively) instead of CJK Symbols and Punctuation (U+3038, U+3039 and U+303A respectively).

An individual Big5 code does not always represent a complete semantic unit. The Big5 codes of logograms are always logograms, 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 CJK double byte character sets, 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 that assumes 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 ( ). 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 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" (, ﹋), 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.

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, unspecified 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.

The original Big 5 only include CJK logograms from the Charts of Standard Forms of Common National Characters (4808 characters) and Less Than Common National Characters (6343 characters), 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. The plethora of variations make UTF 8 or UTF 16 a more consistent code page for modern use.

Microsoft (微軟) created its own version of Big5 extension as Code page 950 for use with Microsoft Windows, which supports the F9D6 F9FE code points from ETEN's extensions. In some versions of Windows, the euro currency symbol is mapped to Big 5 code point A3E1. After installing Microsoft's HKSCS patch on top of traditional Chinese Windows (or any version of Windows 2000 and above with proper language pack), applications using code page 950 automatically use 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.

In contrast to Microsoft's code page 950, IBM's CCSID 950 comprises single byte code page 1114 (CCSID 1114) and double byte code page 947 (CCSID 947). It incorporates ETEN extensions for lead bytes , , and , while omitting those with lead byte (which Microsoft includes), mapping them instead to the Private Use Area as user defined characters. It also includes two non ETEN extension regions with trail bytes , i. e. outside the usual Big5 trail byte range but similar to the Big5+ trail byte range: area 5 has lead bytes and contains IBM selected characters, while area 9 has lead bytes and is a user defined region. IBM refers to the euro sign update of their Big 5 variant as CCSID 1370, which includes both single byte and double byte euro signs. It comprises single byte code page 1114 (CCSID 5210) and double byte code page 947 (CCSID 21427). For better compatibility with Microsoft's variant in IBM Db2, IBM also define the pure double byte Code page 1372 and the associated variable width CCSID 1373, which corresponds to Microsoft's code page 950. IBM assigns CCSID 5471 to the HKSCS 2001 Big5 code page (with CPGID 1374 as CCSID 5470 as the double byte component), CCSID 9567 to the HKSCS 2004 code page (with CPGID 1374 as CCSID 9566 as the double byte component), and CCSID 13663 to the HKSCS 2008 code page (with CPGID 1374 as CCSID 13662 as the double byte component), while CCSID 1375 is assigned to a growing HKSCS code page, currently equivalent to CCSID 13663.

ChinaSea fonts (中國海字集) are Traditional Chinese fonts made by ChinaSea. The fonts are rarely sold separately, but are bundled with other products, such as the Chinese version of Microsoft Office 97. The fonts support Japanese kana, kokuji, and other characters missing in Big 5. As a result, the ChinaSea extensions have become more popular than the government supported extensions. Some Hong Kong BBSes had used encodings in ChinaSea fonts before the introduction of HKSCS.

The 'Sakura' font (日和字集 Sakura Version) is developed in Hong Kong and is designed to be compatible with HKSCS. It adds support for kokuji and proprietary dingbats (including Doraemon) not found in HKSCS.

Unicode at on (Unicode補完計畫), formerly BIG5 extension, extends BIG 5 by altering code page tables, but uses the ChinaSea extensions starting with version 2. However, with the bankruptcy 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. Despite the problems, characters previously mapped to Unicode Private Use Area are remapped to the standardized equivalents when exporting characters to Unicode format.

The web sites of the Oriental Daily News and Sun Daily, belonging to the Oriental Press Group Limited (東方報業集團有限公司) in Hong Kong, used a downloadable font with a different Big 5 extension coding than the HKSCS.

The Taiwan Ministry of Education supplied its own font, the Taiwan Ministry of Education font (臺灣教育部造字檔) for use internally.

Taiwan's Council of Agriculture font, Executive Yuan introduced a 133 character custom font, the Taiwan Council of Agriculture font (臺灣農委會常用中文外字集) that includes 84 characters from the fish radical and 7 from the bird radical.

The Chinese Foundation for Digitization Technology (中文數位化技術推廣委員會) introduced Big5+ in 1997, which used over 20000 code points to incorporate all CJK logograms in Unicode 1.1. However, the extra code points exceeded the original Big 5 definition (Big5+ uses high byte values 81 FE and low byte values 40 7E and 80 FE), preventing it from being installed on Microsoft Windows without new codepage files.

To allow Windows users to use custom fonts, the Chinese Foundation for Digitization Technology introduced Big 5E, which added 3954 characters (in three blocks of code points: 8E40 A0FE, 8140 86DF, 86E0 875C) and removed the Japanese kana from the ETEN extension. Unlike Big 5+, Big5E extends Big 5 within its original definition. Mac OS X 10.3 and later supports Big 5E in the fonts LiHei Pro (儷黑 Pro. ttf) and LiSong Pro (儷宋 Pro. ttf).

The 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 characters introduced in the 1984 ETEN extensions (code points A3C0 A3E0, C6A1 C7F2, and F9D6 F9FE) and the Euro symbol. Cyrillic characters were not included because the authority claimed CNS 11643 does not include such characters.

The Academia Sinica made a Chinese Data Processing font (漢字構形資料庫) in late 1990s, which the latest release version 2.5 included 112,533 characters, some less than the Mojikyo fonts.