Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. NEMOTO
Expires: June 8, 2013 Keio University
December 5, 2012
Mapping characters for precis classes
draft-ietf-precis-mappings-00
Abstract
Preparation and comparison of internationalized strings ("precis")
framework [I-D.ietf-precis-framework] is defining several classes of
strings for preparation and comparison. In the document, case
mapping is defined because many of protocols handle case sensitive or
case insensitive string comparison and therefore preparation of
string is mandatory. As described in IDNA mapping [RFC5895] and
precis problem statement [I-D.ietf-precis-problem-statement],
mappings in internationalized strings are not limited to case, but
also width, delimiters and/or other specials are taken into
consideration. This document is a guideline for authors of protocol
profiles of precis framework and describes the mappings that must be
considered between receiving user input and passing permitted code
points to internationalized protocols.
Status of this Memo
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This Internet-Draft will expire on June 8, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
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1. Introduction
In many cases, user input of internationalized strings is generated
by input method editor ("IME") or copy-and-paste from free text.
Usually users do not care case and/or width of input characters
because they are identical for users' eyes. Further, users rarely
switch IME state to input special characters such as protocol
elements. For Internationalized Domain Names ("IDNs"), IDNA Mapping
[RFC5895] describes methods to treat these issues. For precis
strings, case mapping is defined as a process in precis framework
[I-D.ietf-precis-framework], but width mapping, delimiter mapping
and/or special mapping are not defined. Handling of mappings other
than case is also important to increase chance of strings match as
users expect. This document is a guideline for authors of protocol
profiles of precis framework and describes the mappings that must be
considered between receiving user input and passing permitted code
points to internationalized protocols.
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2. Types of mapping
This document defines two types of mapping. One is protocol
independent mapping that doesn't depend on protocol rules and the
other is protocol dependent mapping that depend on protocol rules.
This document defines some mappings in these mapping types. Authors
of protocol profiles of precis framework should need to give careful
consideration to choice of mappings.
Each mapping type is described in following sections.
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3. Protocol independent mapping
Protocol independent mapping is a mapping that doesn't depend on
protocol rules.
3.1. Width mapping
Fullwidth and halfwidth characters (those defined with Decomposition
Types <wide> and <narrow>) are mapped to their decomposition mappings
as shown in the Unicode character database [Unicode].
Width mapping will increase backward compatibility with Stringprep
[RFC3454] and precis framework [I-D.ietf-precis-framework]. Because
in a Stringprep profile which specifies Unicode normalization form KC
(NFKC) for normalization method, fullwidth/halfwidth characters are
mapped into its compatible form. If a precis framework profile
specified NFKC (which is not recommended), width mapping might not be
useful.
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4. Protocol dependent mapping
Protocol dependent mapping is a mapping that depend on protocol
rules.
4.1. Delimiter mapping
Definitions of delimiters in certain protocols are differ from each
other. Therefore, delimiter mapping table should be based on well
defined mapping table for each protocol.
One of the most useful case of delimiter mapping is when FULL STOP
character (U+002E) is a delimiter as well as domain name. Some of
IME generates FULL STOP compatible characters such as IDEOGRAPHIC
FULL STOP (U+3002) when users type FULL STOP on the keyboard.
4.2. Special mapping
Certain protocols have characters which need to map different
character from precis framework defined mapping rule other than
delimiter characters. In this document, these mappings are named
special mapping. They are differ from each protocol. Therefore,
special mapping table should be based on well defined mapping table
for each protocol. Examples of special mapping are following;
o White spaces are mapped to SPACE (U+0020)
o Some characters such as control characters are mapped to nothing
(Deletion)
LDAPprep[RFC4518] defines the rule that some codepoints(Appendix B.4)
are mapped to SPACE (U+0020).
4.3. Local case mapping
Local case mapping is case folding that depend on language context.
For example, given there is upper case I in a user ID strings, you
should care what's language context that this user ID depend on when
this character is mapped into lower case character. And if this
depends on Turkish, the character should be mapped into LATIN SMALL
LETTER DOTLESS I (U+0131) as this character's lower case.
This document defines characters that need local case mapping based
on the Specialcasing.txt [Specialcasing] in section 3.13 of The
Unicode Standerd [Unicode] to solve such a problem. 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
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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. Conditional
mappings have Language-Insensitive Mappings that targets characters
whose full case mappings do not depend on language, but do depend on
context and Language-Sensitive Mappings that these are characters
whose full case mappings depend on language and perhaps also context.
Of these mappings, characters that Unconditional Mappings and
Language-Insensitive Mappings in Conditional Mappings target are
mapped into same codepoint(s) with just casefolding and special
casefolding then casefolding. But characters that Language-Sensitive
Mappings in Conditional Mappings targets are mapped into different
codepoint with them. Therefore this document defined 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.
A list of characters that need Local case mapping are as follows.
Format:
<Language>; <Codepoint>; <Lowercase>; <Comments>
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
Section 6 "IANA Considerations" contains a template to registry these
characters to IANA as precis local case mapping registry.
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5. Applying order of mapping
Basically, applying order of mapping that this document describes
aren't sensitive. This section defines applying order of mapping to
minimize effect of codepoint change by mappings. This mapping order
is very general and was designed to be acceptable to the widest user
community.
1. width mapping
2. delimiter mapping
3. special mapping
4. local case mapping
5. precis framework
Mappings that this document describes should be performed before
precis framework.
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6. IANA Considerations
6.1. precis local case mapping registry
IANA is requested to create a registry of precis local case mapping.
In accordance with [RFC5226], the registration policy is "RFC
Required".
6.2. Template for precis local case mapping registry
The following information is to be given when a new precis local case
mapping rule is created. The registration template is as follows:
Language: language name
Codepoint: Local case mapping that can be applied when this code
point exists in the strings
Local lowercase: The lowercase codepoint after performing local
case mapping
Comment: Character name of the code point
Appendix C contains further discussion and a table from which that
registry can be initialized.
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7. Security Considerations
TBD.
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8. Acknowledgment
Martin Duerst suggested a need for the case folding about the
mapping(map final sigma to sigma, German sz to ss,.).
Pete Resnick et al. gave important suggestion for this document
during at WG meeting.
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9. 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
Application Protocols", draft-ietf-precis-framework-03
(work in progress), May 2012.
[I-D.ietf-precis-problem-statement]
Blanchet, M. and A. Sullivan, "Stringprep Revision and
PRECIS Problem Statement",
draft-ietf-precis-problem-statement-06 (work in progress),
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July 2012.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
6.1.0", <http://www.unicode.org/versions/Unicode6.1.0/>,
2012.
[Casefolding]
"CaseFolding-6.1.0.txt", Unicode Character Database, July
2011, <http://www.unicode.org/Public/6.1.0/ucd/
CaseFolding.txt>.
[Specialcasing]
"SpecialCasing-6.1.0.txt", Unicode Character Database,
July 2011, <http://www.unicode.org/Public/6.1.0/ucd/
SpecialCasing.txt>.
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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 | - |
+----------------------+-------------+-----------+------+---------+
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Appendix B. Codepoints which need special mapping
B.1. RFC3748
Non-ASCII space characters [StringPrep, C.1.2] that can be mapped to
SPACE (U+0020).
B.2. RFC4013
Non-ASCII space characters [StringPrep, C.1.2] that can be mapped to
SPACE (U+0020).
B.3. RFC4314
Non-ASCII space characters [StringPrep, C.1.2] that can be mapped to
SPACE (U+0020).
B.4. RFC4518
Codepoints mapped to SPACE (U+0020) are following;
U+0009 (CHARACTER TABULATION)
U+000A (LINE FEED (LF))
U+000B (LINE TABULATION)
U+000C (FORM FEED (FF))
U+000D (CARRIAGE RETURN (CR))
U+0085 (NEXT LINE (NEL))
U+0020 (SPACE)
U+00A0 (NO-BREAK SPACE)
U+1680 (OGHAM SPACE MARK)
U+2000 (EN QUAD)
U+2001 (EM QUAD)
U+2002 (EN SPACE)
U+2003 (EM SPACE)
U+2004 (THREE-PER-EM SPACE)
U+2005 (FOUR-PER-EM SPACE)
U+2006 (SIX-PER-EM SPACE)
U+2007 (FIGURE SPACE)
U+2008 (PUNCTUATION SPACE)
U+2009 (THIN SPACE)
U+200A (HAIR SPACE)
U+2028 (Line Separator)
U+2029 (Paragraph Separator)
U+202F (NARROW NO-BREAK SPACE)
U+205F (MEDIUM MATHEMATICAL SPACE)
U+3000 (IDEOGRAPHIC SPACE)
All other control code (e.g., Cc) points or code points with a
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control function (e.g., Cf) are mapped to nothing. Codepoints mapped
to nothing that aren't specified by Stringprep are following;
U+0000-0008
U+000E-001F
U+007F-0084
U+0086-009F
U+06DD
U+070F
U+180E
U+200E-200F
U+202A-202E
U+2061-2063
U+206A-206F
U+FFF9-FFFB
U+1D173-1D17A
U+E0001
U+E0020-E007F
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Appendix C. The initial precis local case mapping registrations
C.1. Lithuanian
language: Lithuanian
Codepoint: U+0049
Local lowercase: U+0069 U+0307
Comment: LATIN CAPITAL LETTER I
Codepoint: U+004A
Local lowercase: U+006A U+0307
Comment: LATIN CAPITAL LETTER J
Codepoint: U+012E
Local lowercase: U+012F U+0307
Comment: LATIN CAPITAL LETTER I WITH OGONEK
Codepoint: U+00CC
Local lowercase: U+0069 U+0307 U+0300
Comment: LATIN CAPITAL LETTER I WITH GRAVE
Codepoint: U+00CD
Local lowercase: U+0069 U+0307 U+0301
Comment: LATIN CAPITAL LETTER I WITH ACUTE
Codepoint: U+0128
Local lowercase: U+0069 U+0307 U+0303
Comment: LATIN CAPITAL LETTER I WITH TILDE
C.2. Turkish
language: Turkish
Codepoint: U+0130
Local lowercase: U+0069
Comment: LATIN CAPITAL LETTER I WITH DOT ABOVE
Codepoint: U+0049
Local lowercase: U+0131
Comment: LATIN CAPITAL LETTER I
C.3. Azerbaijanian
language: Azerbaijanian
Codepoint: U+0130
Local lowercase: U+0069
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Comment: LATIN CAPITAL LETTER I WITH DOT ABOVE
Codepoint: U+0049
Local lowercase: U+0131
Comment: LATIN CAPITAL LETTER I
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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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