[governance] 1999 RFC on core IDN concept by Singapore team - Re: Response to Stephane Bortzmeyer on IDN
David Allen
David_Allen_AB63 at post.harvard.edu
Thu Mar 22 10:06:24 EDT 2007
Here is the core concept filed as an RFC originally in July 1999, by
the Singapore team and the individual who, I believe, was a
leader/member of the Japan chapter of W3C and also a senior figure in
the Unicode Consortium.
Internet Draft James Seng
<draft-jseng-utf5-01.txt> Martin Duerst
28th Jan 2000 Tin Wee Tan
Expires End of July 2000
UTF-5, a transformation format of Unicode and ISO 10646
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
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Internet-Drafts are draft documents valid for a maximum of six
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The list of current Internet-Drafts can be accessed at
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Distribution of this document is unlimited. Please send comments
to the authors at jseng at pobox.org.sg, mduerst at w3.org and
tinwee at post1.com.
Abstract
A new transformation format, called UTF-5 for Unicode is proposed.
The resulting string of this UTF is within a [A-V][0-9] alphanumeric
range. This enables legacy systems or protocols designed for alpha-
numerical character set only to be multilingual enabled and inter-
nationalized immediately. Example of such systems are the domain
name system and email addresses.
1. Introduction
ISO/IEC 10646-1:1993 [ISO-10646] defines a 16 bit character set,
UCS-2 and a 31-bit character set, UCS-4. UCS-2 and UCS-4 are coded
representation forms of the UCS and UCS-4 has no assignments outside
the region correspoding to UCS-2 (the Basic Multilingual Plane, BMP)
at this moment. The UCS-2 and UCS-4 encodings, however, are hard to
use in many current applications and protocols that assume 8 or even
7 bit characters. Even newer systems able to deal with 16 bit char-
acters cannot process UCS-4 data. This situation has led to the
development of so-called UCS transformation formats (UTF), each with
different characteristics.
At this moment, there are 3 standard UTF, namely UTF-7 [UTF7], UTF-8
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[UTF8] and UTF-16 [UTF16], each is a variable length transformation
which gives 7 bit, 8 bit and 16 bit strings respectively. While
these are sufficient for most application uses, there are however
some legacy systems which are, unfortunately, unable to handle even
7 bit strings either due to technical restriction or common uses.
The object of this memo is to propose a UTF-5 which gives a trans-
formed string that is within [A-V][0-9] alphanumerical character set.
This enables legacy systems designed for alphanumerical character set
only to be multilingual enabled and internationalized immediately.
UTF-8 is the preferred transformation format for all new IETF
standards [IETFPC]. UTF-5 is not here to change this. It is proposed
to support legacy applications or protocols that cannot be modified
in a simple way to handle 8 bits using UTF-8 encoding. See Section
4 on the discussion on how UTF-5 can be used for Domain Name System
[DNS] and Simple Mail Transfer Protocol [SMTP] Address.
2. UTF-5 definition
In UTF-5, each character is encoded using a sequence of 1 to 8
octets. Two transformations are needed for UTF-5, namely
1. Determine the quintet ("5-bit") binary sequence.
2. From a table, translate the quintet to the resulting string.
Take note that UTF-5 is not a sequence of quintets but a sequence
of octets where each octets are in the alphanumeric range. Alpha-
numeric is defined as A to V (uppercase only) and 0 to 9 in this
context.
This memo does not specify the binary pattern of the alphanumeric
characters as the purpose of the transformation is to get a alpha-
numeric string which represents a multilingual string. However, it
is presumed that US-ASCII [US-ASCII] is used for most purposes.
2.1 Determine the quintet binary sequence
The first quintet of a binary sequence will have the highest-order
bit set to 1 and the remaining quintet will have the highest-order
bit set to 0. The remaining 4 bits of every quintet contain bits
from the value of the character to be encoded.
The table below summarizes the format of these different quintet
types. The letter x indictes bits available for encoding bits of
the UCS-4 character value.
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UCS-4 range (hex.) UTF-5 quintet sequence (binary)
0000 0000-0000 000F 1xxxx
0000 0010-0000 00FF 1xxxx 0xxxx
0000 0100-0000 0FFF 1xxxx 0xxxx 0xxxx
0000 1000-0000 FFFF 1xxxx 0xxxx 0xxxx 0xxxx
...
1000 0000-7FFF FFFF 1xxxx 0xxxx 0xxxx ..... 0xxxx
2.2 Translation table for quintet and alphanumeric character
The translation table for quintet binary pattern and alphanumeric
character is as follows. This is effectively a duoettrigesimal
(base 32) string representation of the quintets.
quintet quintet quintet quintet
00000 0 01000 8 10000 G 11000 O
00001 1 01001 9 10001 H 11001 P
00010 2 01010 A 10010 I 11010 Q
00011 3 01011 B 10011 J 11011 R
00100 4 01100 C 10100 K 11100 S
00101 5 01101 D 10101 L 11101 T
00110 6 01110 E 10110 M 11110 U
00111 7 01111 F 10111 N 11111 V
2.3 Encoding from UCS-4 to UTF-5
1) Determine the required number of octets from the character value.
Let U be the UCS-4 value, then the required number of octets is
log16(U+1) rounded up.
2) Prepare the quintet binary sequence. Put the highest order bit
of the first quintet as 1 and highest order bit of the rest of
the quintet as 0.
3) Fill in the bits marked x from the bits of the character value,
starting from the lower-order bits of the character value and
putting them first in the last quintet of the sequence, then the
next to last, etc until all x bits are filled in.
4) For each quintet, apply the lookup table in Section 2.2 to get
the corresponding alphanumeric character.
2.4 Decoding UTF-5 to UCS-4
1) Determine the length of the octet sequence. As according to the
UTF-5 encoding, every character will have the inital octet within
the range 'G' to 'V'. Thus, the length of the octet sequence can
be determined by looking for 'G' to 'V' in the UTF-5 string.
2) Apply the reverse lookup according to the table in Section 2.2
to get the quintet binary sequence.
3) Initialize the 4 octets of the UCS-4 character with all bits set
to 0.
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4) Distribute the bits from the sequence to the UCS-4 character,
first the lower-order bits from the last octet of the sequence
and proceeding to the left until no x bits are left.
If the UTF-5 sequence is no more than four octets long, the low
order bits of the result can be interpreated directly as UTF-16
value or equivalently Unicode.
2.5 Detecting a UTF-5 string
As the UTF-5 string is a alphanumeric string, it is difficult to
differentiate between a normal ASCII document or a UTF-5 document.
Nevertheless, if the string is sufficiently long, it is possible to
do some detection of UTF-5 string based on the fact that
1. UTF-5 strings only have characters within '0'-'9' and 'A'-'V'.
2. UTF-5 strings have a well-defined inital octet of 'G' to 'V'.
3. The 'G' character always occurs as the inital and only octet.
In other word, the shortest UTF-5 sequence is "G". For example,
"GF" is not a valid UTF-5 sequence.
3. Examples of UTF-5
The Unicode sequence "A<NOT IDENTICAL TO><ALPHA>." (0041, 2262,
0391, 002E) may be encoded as follows:
"K1I262J91IE"
The Unicode sequence "Hi Mom <WHITE SMILING FACE>!" (0048, 0069,
0020, 004D, 006F, 006D, 0020, 263A, 0021) may be encoded as follows:
"K8M9I0KDMFMDI0I63AI1"
The Unicode sequence representing the Han characters for the
Japanese word "nihongo" (65E5, 672C, 8A9E) may be encoded as
follows:
"M5E5M72COA9E"
Note that from the examples, it is obvious that there is a short-cut
to the UTF-5 transformation which goes like this:
If the hexadecimal notation is 0x00000000, convert it to 'G';
otherwise skip over all leading zeros in the hexadecimal notation
and convert the first non-zero hexadecimal digital as follows:
'1' to 'H', '2' to 'I', ... 'F' to 'V'. Retain all trailing
hexadecimal digits.
4. Applications
There are many applications where UTF-5 would be useful for
Internationalization ("i18n"). Here are some of the possible uses.
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a. Internationalised Domain Names
In the Domain Name System, although the technical standard does not
prevent 8-bits character to be use as domain names, general use of
the system restrict it to only A-Z (upper and lower), 0-9 and "-"
as a valid domain name. This poses great difficulty when doing i18n
of domain names as the current UTF-7, UTF-8 and UTF-16 are not
compatible with the existing software system already in used.
Please join idn at ops.ietf.org to join the discussion on
Internationalised Domain Names "idn". Send an email to
idn-request at ops.ietf.org with the word "subscribe" in the body.
More information on IDN can be found at the following website:
http://www.idns.org/
http://www.imc.org/idn/
b. Internationalization of Simple Mail Transfer Protocol Address
While it is possible for a person to send SMTP Mail in different
languages using different character set to each another using Multi-
purpose Internet Mail Extensions [MIME], the SMTP Mail Address
remains a challenge to be Internationalized. Internationalization of
SMTP Address has two barriers, 1. the Internationalization of Domain
Name System and 2. the Internationalization of the mailbox or
username. SMTP mailbox has a very strict check [RFC822] due to
many potential security risks when using symbols or special char-
acters in mailbox. UTF-5 will allow Unicode to be used as mailbox
with minimal change in system and without additional security risks.
For example, an SMTP Email address for "yamaguchi at asahi.ninhon"
(5C71 53J3 '@' 671D 65E5 '.' 65E5 672C) can be represented in
UTF-5 "LC71L3E3 at M71DM5E5.M5E5M72C". This is a valid [RFC822] Email
address which will not be rejected. It will then be the responsiblity
of the user interface to render "LC71L3E3 at M71DM5E5.M5E5M72C" properly
as "yamaguchi at asahi.ninhon".
Internationalization of URIs is not discussed in this memo. Please
refer to http://www.w3.org/International/0-URL-and-ident.html.
However, uses for UTF-5 extend beyond Internet back to old legacy
systems such as Telegram system or even Morse code allowing
Multilingual characters to be transmitted.
5. Security Considerations
This memo does not address any security consideration at the moment.
6. Acknowledgements
UTF-5 was first defined by Martin Duerst at the University of Zurich
in draft-duerst-dns-i18n-00.txt.
Contributors (not in any order):
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Marc Blanchet <Marc.Blanchet at viagenic.qc.ca>
Paul Gampe <paulg at apnic.net>
Ken Whistler <kenw at sybase.com>
Graham Klyne <GK at ACM.ORG>
7. Bibliography
[ISO-10646] ISO/IEC 10646-1:1993. International Standard --
Information technology -- Universal Multiple-Octet
Coded Character Set (UCS) -- Part 1: Architecture
and Basic Multilingual Plane.
[UNICODE] The Unicode Standard, Version 2.0 (ISBN 0-201-48345-
[UTF-16] 9). The minor reference is Unicode Technical Report
#8, The Unicode Standard, Version 2.1. Refer to URL
http://www.unicode.org/unicode/standard/versions/
[UTF7] Goldsmith, D., and M. Davis, "UTF-7: A Mail-safe
Transformation Format of Unicode", RFC 1642,
Taligent, Inc., July 1994.
[UTF8] F. Yergeau "UTF-8: a transformation format of Unicode
and ISO 10646", RFC2044, Alis Technologies, October
1996.
[US-ASCII] Coded Character Set--7-bit American Standard Code for
Information Interchange, ANSI X3.4-1986.
[DNS] P. Mockapetris "Domain Names - Concepts and
Facilities", RFC1034, ISI, November 1987, "Domain
Names - Implementation and Specification", RFC1035,
ISI, November 1987.
[SMTP] Jonathan B. Postel "Simple Mail Transfer Protocol",
[RFC822] RFC821, ISI, August 1982. David H. Crocker "Standard
for ARPA Internet Text Messages", RFC822, Dept of
Electrical Engineering, Univeristy of Delaware,
August 1982.
[MIME] "Multipurpose Internet Mail Extensions", RFC1341,
N. Borensten, Bellcore, N. Freed, Innosoft, June
1992.
[IETFPC] "IETF Policy on Character Sets and Languages",
RFC2277 BCP18, H. Alvestrand, Jan 1998.
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8. Author Address
James C.H Seng
i-DNS.net International Inc.
102 Elm Street
Menlo Park CA 94025
Tel: (650) 322-6505
E-mail: jseng at pobox.org.sg
Martin J. Duerst
World Wide Web Consortium (W3C)
Keio Research Institute at SFC
Keio University
Fujisawa
252-8520 Japan
Tel: +81 446 49 11 70
E-mail: mduerst at w3.org
NOTE -- Please write the author's name with u-Umlaut wherever
possible, e.g. in HTML as Dürst.
Tin Wee Tan, Dr
National University of Singapore (NUS)
c/o BioInformatic Center
National University Hospital
Lower Kent Ridge Road
Singapore 119074
Tel: +65 774 7149
E-mail: tinwee at post1.com
This memo is also archived at http://www.idns.org/technical.html
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