Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. NEMOTO
Expires: November 25, 2013 Keio University
May 24, 2013
Mapping characters for PRECIS classes
draft-ietf-precis-mappings-02
Abstract
The framework for preparation and comparison of internationalized
strings ("PRECIS") defines several classes of strings for preparation
and comparison. In the framework, case mapping is defined because
many protocols handle case-sensitive or case-insensitive string
comparison and therefore preparation of the string is mandatory. As
described in the mapping for Internationalized Domain Names in
Applications (IDNA) and the PRECIS problem statement, mappings for
internationalized strings are not limited to case, but also width
mapping and mapping of delimiters and other specials can be taken
into consideration. This document provides guidelines for authors of
protocol profiles of the PRECIS framework and describes several
mappings that can be applied between receiving user input and passing
permitted code points to internationalized protocols. The mappings
described here are expected to be applied as Addtional mapping in the
PRECIS framework.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 25, 2013.
Copyright Notice
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Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Protocol dependent mappings . . . . . . . . . . . . . . . . . 3
2.1. Delimiter mapping . . . . . . . . . . . . . . . . . . . . 3
2.2. Special mapping . . . . . . . . . . . . . . . . . . . . . 3
2.3. Local case mapping . . . . . . . . . . . . . . . . . . . 4
3. Order of operations . . . . . . . . . . . . . . . . . . . . . 5
4. Open issues . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Mapping type list each protocol . . . . . . . . . . 7
A.1. Mapping type list for each protocol . . . . . . . . . . . 7
Appendix B. Code points list for local case mapping . . . . . . 8
B.1. Unicode 6.2 . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 8
C.1. Changes since -00 . . . . . . . . . . . . . . . . . . . . 8
C.2. Changes since -01 . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
In many cases, user input of internationalized strings is generated
through the use of an input method editor ("IME") or through copy-
and-paste from free text. Usually users do not care about the case
and/or width of input characters because they appear to be visually
identical. Further, users rarely switch IME state to input special
characters such as protocol elements. For Internationalized Domain
Names ("IDNs"), the IDNA Mapping specification [RFC5895] describes
methods for handling these issues. For PRECIS strings, case mapping
and width mapping are defined in the PRECIS framework specification
[I-D.ietf-precis-framework], but delimiter mapping, special mapping,
and language dependent mapping are not defined. Handling of mappings
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other than case and width is also important to increase chance of
strings match as users expect. This document provides guidelines for
authors of protocol profiles of the PRECIS framework and describes
mappings that can be applied between receiving user input and passing
permitted code points to internationalized protocols. The mappings
described in this document are expected to be applied as Addtional
mapping in the PRECIS framework.
2. Protocol dependent mappings
The PRECIS framework defines several protocol-independent mappings.
The additional mappings defined in this document are protocol-
dependent, i.e., they depend on the rules for a particular
application protocol.
2.1. Delimiter mapping
Some application protocols define delimiters for use in such
protocols, but the delimiters are different for each protocols.
Therefore, the delimiter mapping table should be based on a well-
defined mapping table for each protocol.
Delimiter mapping is supposed to map delimiter characters that have
compatible characters to canonical characters. For example, '@' in
mail address or ':' and '/' in URI has width compatible character.
And '+', '-', '<' and '>' may be such character. Another example is
the FULL STOP character (U+002E) which is a delimiter in the visual
presentation of domain names. Some IMEs generate semantic or width
compatible character of FULL STOP such as IDEOGRAPHIC FULL STOP
(U+3002) when a user types FULL STOP on the keyboard. Such FULL STOP
compatible characters need to be mapped to the FULL STOP before
passing the string to the protocol.
2.2. Special mapping
Aside from delimiter characters, certain protocols have characters
which need to be mapped in ways that are different from the rules
specified in the PRECIS framework (e.g., mapping non-ASCII space
characters to ASCII space). In this document, these mappings are
called "special mappings". They are different for each protocol.
Therefore, the special mapping table should be based on a well-
defined mapping table for each protocol. Examples of special mapping
are the following;
o White spaces are mapped to SPACE (U+0020)
o Some characters such as control characters are mapped to nothing
(Deletion)
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As examples, EAP [RFC3748], SASLprep [RFC4013], IMAP4 ACL [RFC4314]
and LDAPprep [RFC4518] define the rule that some codepoints for non-
ASCII space are mapped to SPACE (U+0020).
2.3. Local case mapping
Local case mapping is case folding that depends on language and
context. For example, the mapping of LATIN CAPITAL LETTER I (U+0049)
depends on the language context of the user: if the language is
Turkish (or one of several other languages), the character should be
mapped into LATIN SMALL LETTER DOTLESS I (U+0131) as this character's
lower case equivalent.
To solve such problems for PRECIS framework, this document defines
characters that need local case mapping based on the
Specialcasing.txt [Specialcasing] file in section 3.13 of The Unicode
Standard [Unicode]. Local case mapping targets only characters that
get two different results to perfom just casefolding that is defined
in the Casefolding.txt [Casefolding] and perfom special casefolding
that is defined in the Specialcasing.txt then casefolding, because
PRECIS framework have casefolding.
There are two types casefoldings defined as Unconditional Mappings
and Conditional Mappings in the Specialcasing.txt file. Conditional
mappings have Language-Insensitive Mappings that target characters
whose full case mappings do not depend on language, but do depend on
context. Language-Sensitive Mappings that these are characters whose
full case mappings depend on language and perhaps also context.
Of these mappings, characters with Unconditional Mappings or with
Language-Insensitive Mappings in Conditional Mappings target are
mapped into same codepoint(s) with just casefolding or special
casefolding then casefolding. But characters with Language-Sensitive
Mappings in Conditional Mappings targets are mapped into different
codepoints. Therefore this document defines characters that are a
part of characters of Lithuanian(lt), Turkish(tr) and
Azerbaijanian(az) that Language-Sensitive Mappings targets as targets
for local case mapping.
The following are the methods to calculate codepoints that local case
mapping targets. Here Casefolding() means casefolding described in
the Casefolding.txt file [Casefolding] and Specialcasing() means
specialcasing described in the Specialcasing.txt file
[Specialcasing].
If Casefolding(Specialcasing(cp)) != Casefolding(cp)
Then cp is a target
Else cp is not a target;
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Application developers should calculate codepoints that local case
mapping targets by using the latest Casefolding.txt and
Specialcasing.txt. Appendix B "Code points list for local case
mapping" lists codepoints in Unicode 6.2 calculated by this method.
3. Order of operations
The mappings described in this document are expected to be applied as
Addtional mapping in the PRECIS framework. Basically, the mappings
described in this document describes could be applied in any order.
However, this section specifies a particular order to minimize the
effect of codepoint changes introduced by the mappings. This mapping
order is very general and was designed to be acceptable to the widest
user community.
1. Delimiter mapping
2. Special mapping
3. Local case mapping
4. Open issues
Followings are current open issues for this document.
1. Some protocols requires local case mapping as normative of the
PRECIS framework. Is it necessary to define the local case
mapping in the framework document? Issue here is that the local
case mapping is for localizaion and the PRECIS framework is for
internationalization. Following to IDNA2008, PRECIS core
protocol should concentrate to internationalization, and
localization should be separated from the core protocol (like
this document).
5. Security Considerations
As well as Mapping Characters for IDNA2008 [RFC5895], this document
suggests creating mappings that might cause confusion for some users
while alleviating confusion in other users. Such confusion is not
covered in any depth in this document.
6. IANA Considerations
This document has no actions for the IANA.
7. Acknowledgment
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Martin Duerst suggested a need for the case folding about the mapping
(map final sigma to sigma, German sz to ss,.).
Joe Hildebrand, John Klensin, Marc Blanchet, Pete Resnick and Peter
Saint-Andre, et al. gave important suggestion for this document
during at WG meeting.
8. References
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", RFC
3491, March 2003.
[RFC3722] Bakke, M., "String Profile for Internet Small Computer
Systems Interface (iSCSI) Names", RFC 3722, April 2004.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, February 2005.
[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
RFC 4314, December 2005.
[RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Internationalized String Preparation", RFC 4518,
June 2006.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, September 2010.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 6122, March 2011.
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation and Comparison of Internationalized Strings in
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Application Protocols", draft-ietf-precis-framework-06
(work in progress), September 2012.
[I-D.ietf-precis-problem-statement]
Blanchet, M. and A. Sullivan, "Stringprep Revision and
PRECIS Problem Statement", draft-ietf-precis-problem-
statement-08 (work in progress), September 2012.
[Unicode] The Unicode Consortium, , "The Unicode Standard, Version
6.2.0", ,
2012.
[Casefolding]
, "CaseFolding-6.2.0.txt", Unicode Character Database,
July 2011,
,
.
[Specialcasing]
, "SpecialCasing-6.2.0.txt", Unicode Character Database,
July 2011, , .
[ISO.3166-1]
International Organization for Standardization, "Codes for
the representation of names of countries and their
subdivisions - Part 1: Country codes", ISO Standard 3166-
1:1997, 1997.
Appendix A. Mapping type list each protocol
A.1. Mapping type list for each protocol
This table is the mapping type list for each protocol. Values marked
"o" indicate that the protocol use the type of mapping. Values
marked "-" indicate that the protocol doesn't use the type of
mapping.
+----------------------+-------------+-----------+------+---------+
| \ Type of mapping | Width | Delimiter | Case | Special |
| RFC \ | (NFKC) | | | |
+----------------------+-------------+-----------+------+---------+
| 3490 | - | o | - | - |
| 3491 | o | - | o | - |
| 3722 | o | - | o | - |
| 3748 | o | - | - | o |
| 4013 | o | - | - | o |
| 4314 | o | - | - | o |
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| 4518 | o | - | o | o |
| 6120 | - | - | o | - |
+----------------------+-------------+-----------+------+---------+
Appendix B. Code points list for local case mapping
Followings are a list of characters that need Local case mapping.
Format:
; ; ;
means the alpha-2 codes in [ISO.3166-1].
B.1. Unicode 6.2
lt; 0049; 0069 0307; LATIN CAPITAL LETTER I
lt; 004A; 006A 0307; LATIN CAPITAL LETTER J
lt; 012E; 012F 0307; LATIN CAPITAL LETTER I WITH OGONEK
lt; 00CC; 0069 0307 0300; LATIN CAPITAL LETTER I WITH GRAVE
lt; 00CD; 0069 0307 0301; LATIN CAPITAL LETTER I WITH ACUTE
lt; 0128; 0069 0307 0303; LATIN CAPITAL LETTER I WITH TILDE
tr; 0130; 0069; LATIN CAPITAL LETTER I WITH DOT ABOVE
tr; 0049; 0131; LATIN CAPITAL LETTER I
az; 0130; 0069; LATIN CAPITAL LETTER I WITH DOT ABOVE
az; 0049; 0131; LATIN CAPITAL LETTER I
Appendix C. Change Log
C.1. Changes since -00
o Modify the Section 2.3 "Local case mapping" to specify the method
to calculate codepoints that local case mapping targets.
o Add the Section 4 "Open issues".
o Modify the Section 6 "IANA Considerations".
o Modify the Section 5 "Security Considerations".
o Remove the "The initial PRECIS local case mapping registrations".
o Add the Appendix B "Code points list for local case mapping".
o Add the Appendix C "Change Log".
C.2. Changes since -01
o Unified PRECIS notation in all capital letters as well as other
documents.
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o Removed the Section 1 "Types of mapping" and the Section 2
"Protocol independent mapping" because width mapping is now in
framework document.
o Added relationship between the framework document and this
document in the Section 3 "Order of operations".
o Updated the Section 4 "Open issues" to address new issue raised on
mailing list.
o Move the Section 6 "IANA Considerations" after the Section 5
"Security Considerations".
o Remove the Appendix B "Codepoints which need special mapping" and
mentioned related documents in the Section 2.2 .
Authors' Addresses
Yoshiro YONEYA
JPRS
Chiyoda First Bldg. East 13F
3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065
Japan
Phone: +81 3 5215 8451
Email: yoshiro.yoneya@jprs.co.jp
Takahiro NEMOTO
Keio University
Graduate School of Media Design
4-1-1 Hiyoshi, Kohoku-ku
Yokohama, Kanagawa 223-8526
Japan
Phone: +81 45 564 2517
Email: t.nemo10@kmd.keio.ac.jp
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