Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. NEMOTO
Expires: August 13, 2012 Keio University
February 10, 2012
Mapping characters for PRECIS classes
draft-yoneya-precis-mappings-01
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 considers mappings other than case
mapping in PRECIS context.
Status of this Memo
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This Internet-Draft will expire on August 13, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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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 considers such mappings in PRECIS
context.
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2. Type of mappings
2.1. 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]. This mapping
should be performed before case mapping because fullwidth/halfwidth
characters includes both upper case and lower case letters.
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.
2.2. 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 protocols. This mapping should be
performed after width mapping because some punctuations have
fullwidth form.
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.
2.3. Special mapping
Certain protocols defined special mapping. And they are differ from
each other. Therefore, special mapping table should be based on well
defined mapping table for each protocols. For example,
LDAPprep[RFC4518] defines the rule that some codepoints(Appendix B.4)
are mapped to SPACE (U+0020). This mapping should be performed after
width mapping because some punctuations have fullwidth form. But,
there is no preferred order of delimiter mapping and special mapping.
See Section 3 for more detail.
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3. Discussion
There are several points for discussion on this topic.
o Is delimiter mapping a part of special mapping? If it is not a
part of special mapping, whether order of handling about special
mapping should be performed before or after delimiter mapping?
Are delimiters and other specials mutually orthogonal? If they
are, their order of handling is not important. But if not, how is
their order of handling made?
o Is additional case mapping considered? Does the case folding for
special characters (final sigma(U+03C2), German sz(U+00DF),
Turkish I with dot above(U+0130), or dotless i(U+0131) ...) need
special handling?
o Whether mappings other than case are targets of PRECIS or not? If
they are target, are they a part of PRECIS Framework
[I-D.ietf-precis-framework] or separate ones like IDNA Mapping
[RFC5895] specification?
o Are there another mappings not described in this document? For
example, migration from Stringprep [RFC3454] to PRECIS Framework
[I-D.ietf-precis-framework] needs some special treatment?
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4. IANA Considerations
TBD.
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5. Security Considerations
TBD.
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6. Acknowledgment
Martin Duerst suggested a need for the case folding about the
mapping(map final sigma to sigma, German sz to ss,.).
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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.
[I-D.ietf-precis-framework]
Blanchet, M. and P. Saint-Andre, "PRECIS Framework:
Handling Internationalized Strings in Protocols",
draft-ietf-precis-framework-01 (work in progress),
October 2011.
[I-D.ietf-precis-problem-statement]
Blanchet, M. and A. Sullivan, "Stringprep Revision Problem
Statement", draft-ietf-precis-problem-statement-04 (work
in progress), January 2012.
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[Unicode] The Unicode Consortium, "The Unicode Standard, Version
6.1.0", http://www.unicode.org/versions/Unicode6.1.0/,
2012.
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Appendix A. Mapping type list each protocols
A.1. Mapping type list for each protocols
This table is the mapping type list for each protocols. 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. Change Log
C.1. Changes since -00
o Add the Section 2.3 "Special mapping" in Section 2 Type of
mappings.
o Add the topic about the special mapping and additional case
mapping in Section 3 Discussion.
o Add Appendices;
Appendix A "Mapping type list each protocols"
Appendix B "Code point list is need special mapping"
Appendix C "Change Log"
o Add the Section 6 Acknowledgment.
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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
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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