VISCII is an unofficially defined modified ASCII character encoding for using the Vietnamese language with computers. It should not be confused with the similarly named officially registered VSCII encoding. VISCII keeps the 95 printable characters of ASCII unmodified, but it replaces 6 of the 33 control characters with printable characters. It adds 128 precomposed characters. Unicode and the Windows-1258 code page are now used for virtually all Vietnamese computer data, but legacy VSCII and VISCII files may need conversion.

History and naming

VISCII was designed by the Vietnamese Standardization Working Group (Viet-Std Group) led by Christopher Cuong T. Nguyen, Cuong M. Bui, and Hoc D. Ngo based in Silicon Valley, California in 1992 while they were working with the Unicode consortium to include pre-composed Vietnamese characters in the Unicode standard. VISCII, along with VIQR, was first published in a bilingual report in September 1992, in which it was dubbed the "Vietnamese Standard Code for Information Interchange". The report noted a proliferation in computer usage in Vietnam and the increasing volume of computer-based communications among Vietnamese abroad, that existing applications used vendor-specific encodings which were unable to interoperate with one another, and that standardisation between vendors was therefore necessary. The successful inclusion of composed and precomposed Vietnamese in Unicode 1.0 was the result of the lessons learned from the development of 8-bit VISCII and 7-bit VIQR. This defined a character encoding named VSCII, which had been developed by the TCVN Technical Committee on Information Technology (TCVN/TC1), and with its name standing for "Vietnamese Standard Code for Information Interchange". Unlike VISCII, VSCII is a "Vietnamese Standard" in the sense of a national standard.

VISCII and VIQR were approved as the informational-status , attributed to the Viet-Std group and dated May 1993. As is the case with IETF RFCs, <nowiki>RFC 1456</nowiki> notes them to be "conventions" used by overseas Vietnamese speakers on Usenet, and that it "specifies no level of standard". In spite of this, it continues to call VISCII the "VIetnamese Standard Code for Information Interchange" (the same name taken by VSCII). The labels <code>VISCII</code> and <code>csVISCII</code> are registered with the IANA for VISCII, with reference to <nowiki>RFC 1456</nowiki>. (There is, on the other hand, no official IANA label for TCVN 5712 / VSCII, although <code>x-viet-tcvn5712</code> was previously supported by Mozilla Firefox.)

Design

A traditional extended ASCII character set consists of the ASCII set plus up to 128 characters. Vietnamese requires 134 additional letter-diacritic combinations, which is six too many. There are (short of dropping tone mark support for capital letters, as in VSCII-3) essentially four different ways to handle this problem:

  1. Use variable-width encoding (as does UTF-8)
  2. Include combining diacritical marks for tone marks (as do VSCII-2 and Windows-1258) or for diacritics in general (as do ANSEL and VNI)
  3. Replace some ASCII punctuation, preferably punctuation which is not invariant in ISO 646 (as does VNI for DOS)
  4. Replace at least six of the basic ASCII control characters (as do VPS and VSCII-1)

VISCII went for the last option, replacing six of the least problematic (e.g., least likely to be recognised by an application and acted on specially) C0 control codes (STX, ENQ, ACK, DC4, EM, and RS) with six of the least-used uppercase letter-diacritic combinations. It was also supported by the Windows Vietnamese keyboard software, WinVNKey, created by Christopher Cuong T. Nguyen and later upgraded through various Windows versions by Hoc D. Ngo and others.

VISCII was mostly used by overseas Vietnamese speakers, with VSCII (TCVN) being more popular in northern Vietnam and VNI being more popular in southern Vietnam.

Character set

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See also

  • ASCII
  • Vietnamese Quoted-Readable (VIQR)
  • Vietnamese Standard Code for Information Interchange (VSCII)
  • Windows-1258

References

Further reading

  • <!-- -->
  • https://www.math.nmsu.edu/~mleisher/Software/csets/VISCII.TXT<!-- https://web.archive.org/web/20170219001026/https://www.math.nmsu.edu/~mleisher/Software/csets/VISCII.TXT -->
  • - Conventions for Encoding the Vietnamese Language
  • Vietnamese-Standardization Working Group based in California
  • Viet-Std Report 1992
  • AnGiang Software
  • VISCII-compliant software and fonts for MS-DOS and Windows
  • VISCII-compliant software, libraries, and fonts for Unix
  • WinVNKey, Vietnamese keyboard driver for Windows supporting multinational character sets, including VISCII
  • MacVNKey, VISCII-compliant keyboard driver for Macintosh classic