Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. Nemoto
Expires: April 21, 2014 Keio University
October 18, 2013
Mapping characters for PRECIS classes
draft-ietf-precis-mappings-04
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.
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 April 21, 2014.
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 . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative 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 . . . . . . 7
B.1. Unicode 6.3 . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 8
C.1. Changes since -00 . . . . . . . . . . . . . . . . . . . . 8
C.2. Changes since -01 . . . . . . . . . . . . . . . . . . . . 8
C.3. Changes since -02 . . . . . . . . . . . . . . . . . . . . 9
C.4. Changes since -03 . . . . . . . . . . . . . . . . . . . . 9
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. Users in general do not care about the
case and/or width of input characters because they consider those
characters to be functionally equivalent or visually identical.
Furthermore, users rarely switch IME state to input special
characters such as protocol elements. For Internationalized Domain
Names ("IDNs"), the IDNA Mapping specification [RFC5895] describes
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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;
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o White spaces are mapped to SPACE (U+0020)
o Some characters such as control characters are mapped to nothing
(Deletion)
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
The purpose of local case mapping is to increase the probability of
matching-result from the comparison between uppercase and lowercase
characters, targeting locale and locale and context-dependent
characters.
As an example of locale and context-dependent mapping, LATIN CAPITAL
LETTER I (U+0049) is normally mapped to LATIN SMALL LETTER I
((U+0069); however, if the language is Turkish (or one of several
other languages), unless an I is before a dot_above, then the
character should be mapped to LATIN SMALL LETTER DOTLESS I (U+0131).
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].
The following are the methods to calculate codepoints that local case
mapping targets. Here Casefolding() means full 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;
Local case mapping can be selected only when case mapping is selected
using the PRECIS Framework profile. 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 6.3
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
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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 Duerst suggested a need for the case folding about the mapping
(map final sigma to sigma, German sz to ss,.).
Alexey Melnikov, Andrew Sullivan, Joe Hildebrand, John Klensin, Marc
Blanchet, Pete Resnick and Peter Saint-Andre, et al. gave important
suggestion for this document during at WG meeting and WG LC.
7. References
7.1. Normative References
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation and Comparison of Internationalized Strings in
Application Protocols", draft-ietf-precis-framework-06
(work in progress), September 2012.
[Unicode] The Unicode Consortium, ., "The Unicode Standard, Version
6.3.0", ,
2012.
[Casefolding]
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, "CaseFolding-6.3.0.txt", Unicode Character Database,
July 2011,
,
.
[Specialcasing]
, "SpecialCasing-6.3.0.txt", Unicode Character Database,
July 2011, , .
7.2. Informative 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.
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[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and
Problem Statement for the Preparation and Comparison of
Internationalized Strings (PRECIS)", RFC 6885, March 2013.
[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:
; ; ;
means the alpha-2 codes in [ISO.3166-1].
B.1. Unicode 6.3
0049; 0069 0307; lt More_Above; # LATIN CAPITAL LETTER I
004A; 006A 0307; lt More_Above; # LATIN CAPITAL LETTER J
00CC; 0069 0307 0300; lt; # LATIN CAPITAL LETTER I WITH GRAVE
00CD; 0069 0307 0301; lt; # LATIN CAPITAL LETTER I WITH ACUTE
0128; 0069 0307 0303; lt; # LATIN CAPITAL LETTER I WITH TILDE
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012E; 012F 0307; lt More_Above; # LATIN CAPITAL LETTER I WITH
OGONEK
0307; 0307; lt After_Soft_Dotted; # COMBINING DOT ABOVE
0049; 0131; tr Not_Before_Dot; # LATIN CAPITAL LETTER I
0130; 0069; tr; # LATIN CAPITAL LETTER I WITH DOT ABOVE
0307; ; tr After_I; # COMBINING DOT ABOVE
0049; 0131; az Not_Before_Dot; # LATIN CAPITAL LETTER I
0130; 0069; az; # LATIN CAPITAL LETTER I WITH DOT ABOVE
0307; ; az After_I; # COMBINING DOT ABOVE
Appendix C. Change Log
C.1. Changes since -00
o Modify the Section 4.3 "Local case mapping" to specify the method
to calculate codepoints that local case mapping targets.
o Add the Section 6 "Open issues".
o Modify the Section 7 "IANA Considerations".
o Modify the Section 8 "Security Considerations".
o Remove the "The initial PRECIS local case mapping registrations".
o Add the Appendix C "Code points list for local case mapping".
o Add the Appendix D "Change Log".
C.2. Changes since -01
o Unified PRECIS notation in all capital letters as well as other
documents.
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".
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o Remove the Appendix B "Codepoints which need special mapping" and
mentioned related documents in the Section 2.2 .
C.3. Changes since -02
o Removed the "Open issues".
C.4. Changes since -03
o Modify the Section 1 "Introduction" in more clear text.
o Modify the Section 2.3 "Local case mapping" to clarify the purpose
of the local case mapping and an example, and add restriction to
use with PRECIS Framework.
o Change the format in the Appendix B "Code points list for local
case mapping".
o Split the Section 7 "References" into "Normative References" and
"Informative References"
o Update the Unicode version 6.2 to 6.3 in this document.
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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