Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. Nemoto
Expires: February 08, 2014 Keio University
August 07, 2013

Mapping characters for PRECIS classes
draft-ietf-precis-mappings-03

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 Additional mapping in the PRECIS framework.

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Table of Contents

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 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 Additional 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; [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).

As examples, EAP

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 perform just casefolding that is defined in the Casefolding.txt [Casefolding] and perform 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;

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 Additional 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. 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.

5. IANA Considerations

This document has no actions for the IANA.

6. Acknowledgment

Martin Dürst 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.

7. 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.
[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and Problem Statement for the Preparation and Comparison of Internationalized Strings (PRECIS)", RFC 6885, March 2013.
[I-D.ietf-precis-framework] Saint-Andre, P. and M. Blanchet, "PRECIS Framework: Preparation and Comparison of Internationalized Strings in Application Protocols", Internet-Draft draft-ietf-precis-framework-06, September 2012.
[Unicode] The Unicode Consortium, , "The Unicode Standard, Version 6.2.0", <http://www.unicode.org/versions/Unicode6.2.0/>, 2012.
[Casefolding] , , "CaseFolding-6.2.0.txt", Unicode Character Database, July 2011, <http://www.unicode.org/Public/6.2.0/ucd/CaseFolding.txt>, .
[Specialcasing] , , "SpecialCasing-6.2.0.txt", Unicode Character Database, July 2011, <http://www.unicode.org/Public/6.2.0/ucd/SpecialCasing.txt>, .
[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    |
|         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:
<Language>; <Codepoint>; <Lowercase>; <Comments>
<Language> means the alpha-2 codes in [ISO.3166-1].

B.1. Unicode 6.2

Appendix C. Change Log

C.1. Changes since -00

C.2. Changes since -01

C.3. Changes since -02

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