Network Working Group Y. YONEYA
Internet-Draft JPRS
Intended status: Informational T. Nemoto
Expires: November 7, 2015 Keio University
May 6, 2015
Mapping characters for PRECIS classes
draft-ietf-precis-mappings-10
Abstract
The framework for preparation and comparison of internationalized
strings ("PRECIS") defines several classes of strings for preparation
and comparison. Case mapping is defined because many protocols
perform case-sensitive or case-insensitive string comparison and so
preparation of the string is mandatory. The Internationalized Domain
Names in Applications (IDNA) and the PRECIS problem statement
describes mappings for internationalized strings that are not limited
to case, but include width mapping and mapping of delimiters and
other specials that 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 an additional mapping and locale-/context-
dependent case mapping.
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 7, 2015.
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Copyright Notice
Copyright (c) 2015 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol dependent mappings . . . . . . . . . . . . . . . . . 3
2.1. Delimiter mapping . . . . . . . . . . . . . . . . . . . . 3
2.2. Special mapping . . . . . . . . . . . . . . . . . . . . . 4
2.3. Local case mapping . . . . . . . . . . . . . . . . . . . 4
3. Order of operations . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Mapping type list each protocol . . . . . . . . . . 7
A.1. Mapping type list for each protocol . . . . . . . . . . . 7
Appendix B. The reason why local case mapping is alternative to
case mapping in PRECIS framework . . . . . . . . . . 8
Appendix C. Limitation to local case mapping . . . . . . . . . . 8
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 9
D.1. Changes since -00 . . . . . . . . . . . . . . . . . . . . 9
D.2. Changes since -01 . . . . . . . . . . . . . . . . . . . . 9
D.3. Changes since -02 . . . . . . . . . . . . . . . . . . . . 9
D.4. Changes since -03 . . . . . . . . . . . . . . . . . . . . 10
D.5. Changes since -04 . . . . . . . . . . . . . . . . . . . . 10
D.6. Changes since -05 . . . . . . . . . . . . . . . . . . . . 10
D.7. Changes since -06 . . . . . . . . . . . . . . . . . . . . 10
D.8. Changes since -07 . . . . . . . . . . . . . . . . . . . . 11
D.9. Changes since -08 . . . . . . . . . . . . . . . . . . . . 11
D.10. Changes since -09 . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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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 generally 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 the 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]. Further, the handling of mappings other
than case and width, such as delimiter, special, and local case, are
also important in order to increase the probability that the
resulting strings compare as users expect. 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 delimiter mapping and special mapping rules described
here are applied as "additional mappings" beyond those defined in the
PRECIS framework, whereas the "local case mapping" rule provides
locale-dependent and context-dependent alternative case mappings for
specific target characters.
2. Protocol dependent mappings
The PRECIS framework defines several protocol-independent mappings.
The additional mappings and local case mapping 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 their own use,
resulting in the fact that the delimiters are different for each
protocol. The delimiter mapping table should therefore be based on a
well-defined mapping table for each protocol.
Delimiter mapping is used to map characters that are similar to
protocol delimiters into the canonical delimiter characters. For
example, there are width-compatible characters that correspond to the
'@' in email addresses and the ':' and '/' in URIs. The '+', '-',
'<' and '>' characters are other common delimiters that might require
such mapping. For the FULL STOP character (U+002E), a delimiter in
the visual presentation of domain names, some IMEs produce a
character such as IDEOGRAPHIC FULL STOP (U+3002) when a user types
FULL STOP on the keyboard. In all these cases, the visually similar
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characters that can come from user input need to be mapped to the
correct protocol delimiter characters before the string is passed 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)
As examples, EAP [RFC3748], SASLprep [RFC4013], IMAP4 ACL [RFC4314]
and LDAPprep [RFC4518] define the rule that some codepoints for the
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
results that users expect when character case is changed (e.g., map
uppercase to lowercase) between input and use in a protocol. Local
case mapping selectively affects characters whose case mapping
depends on locale and/or context.
As an example of locale and context-dependent mapping, LATIN CAPITAL
LETTER I ("I", U+0049) is normally mapped to LATIN SMALL LETTER I
("i", U+0069); however, if the case of Turkish (or one of several
other languages), unless an I is before a dot_above, the character
should be mapped to LATIN SMALL LETTER DOTLESS I (U+0131).
Case mapping using Unicode Default Case Folding in PRECIS framework
does not consider such locale or context because it is a common
framework for internationalization. Local case mapping defined in
this document corresponds to demands from applications which supports
users' locale and/or context. The complete set of possible target
characters for local case mapping are the characters specified in the
SpecialCasing.txt [Specialcasing] file in section 3.13 of the Unicode
Standard [Unicode], but the specific set of target characters
selected for local case mapping depends on locale and/or context, as
further explained in the SpeicalCasing.txt file.
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The case folding method for a selected target character is to map
into lower case as defined in SpecialCasing.txt. The case folding
method for all other, non-target characters is as specified in
Section 4.1.3 of the PRECIS framework (i.e., It is RECOMMENDED to use
Unicode Default Case Folding for all non-target characters). When an
application supports users' locale and/or context, use of local case
mapping can increase the probability that string comparisons yield
the results that users expect.
If Unicode Default Case Folding is selected as "Case Mapping" in
PRECIS profiles registry, PRECIS profile designers may consider
whether local case mapping can be applied. And if it can be applied,
it is better to add "local case mapping is applicable alternatively"
after "Unicode Default Case Folding" for note to application
developers. The reason why local case mapping is alternative to
Unicode Default Case Folding is written in the Appendix B.
3. Order of operations
Delimiter mapping and special mapping described in this document are
expected to be applied as additional mappings in the PRECIS
framework. The mappings described in this document could be applied
in any order. This section specifies a particular order to minimize
the effect of codepoint changes introduced by the mappings. This
mapping order is very general and has been designed to be acceptable
to the widest user community.
1. Delimiter mapping
2. Special 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,.).
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Alexey Melnikov, Andrew Sullivan, Barry Leiba, David Black, Heather
Flanagan, 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, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
draft-ietf-precis-framework-23 (work in progress),
February 2015.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
7.0.0", ,
2012.
[Casefolding]
The Unicode Consortium, "CaseFolding-7.0.0.txt", Unicode
Character Database, July 2011,
.
[Specialcasing]
The Unicode Consortium, "SpecialCasing-7.0.0.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.
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[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.
[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.
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+----------------------+-------------+-----------+------+---------+
| Protocol and | Width | Delimiter | Case | Special |
| mapping RFC | (NFKC) | | | |
+----------------------+-------------+-----------+------+---------+
| IDNA (RFC 3490) | - | o | - | - |
| IDNA (RFC 3491) | o | - | o | - |
| iSCSI (RFC 3722) | o | - | o | - |
| EAP (RFC 3748) | o | - | - | o |
| SASL (RFC 4013) | o | - | - | o |
| IMAP (RFC 4314) | o | - | - | o |
| LDAP (RFC 4518) | o | - | o | o |
| XMPP (RFC 6120) | - | - | o | - |
+----------------------+-------------+-----------+------+---------+
Appendix B. The reason why local case mapping is alternative to case
mapping in PRECIS framework
One outstanding issue regarding full case folding for characters is,
the character "LATIN SMALL LETTER SHARP S" (U+00DF) (hereinafter
referred to as "eszett") becomes two "LATIN SMALL LETTER S"s (U+0073
U+0073) by performing the case mapping using Unicode Default Case
Folding in the PRECIS framework. On the other hand, eszett doesn't
become a different codepoint by performing the case mapping in
SpecialCasing.txt. If local case mapping in this document is not an
alternative to case mapping in PRECIS framework, PRECIS profile
designers can select both mappings, therefore, German's eszett can
not keep the locale if the case mapping in the PRECIS framework was
performed after the local case mapping.
Appendix C. Limitation to local case mapping
As described in section Section 2.3, the possible target characters
of local case mapping are specified in SpecialCasing.txt. The
Unicode Standard (at least, up to version 7.0.0) does not define any
context-dependent mappings between "GREEK SMALL LETTER SIGMA"
(U+03C3) (hereinafter referred to as "small sigma") and "GREEK SMALL
LETTER FINAL SIGMA" (U+03C2) (hereinafter referred to as "final
sigma"). Thus, local case mapping is not applicable to small sigma
or final sigma, so case mapping in the PRECIS framework always maps
final sigma to small sigma, independent of context, as specified by
Unicode Default Case Folding. (Note: Following comments are from
SpecialCasing.txt.)
# Note: the following cases are not included, since they would
case-fold in lowercasing
# 03C3; 03C2; 03A3; 03A3; Final_Sigma; # GREEK SMALL LETTER SIGMA
# 03C2; 03C3; 03A3; 03A3; Not_Final_Sigma; # GREEK SMALL LETTER
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Local case mapping follows Unicode definition, so mapping of small
sigma and final sigma is up to the definition.
Appendix D. Change Log
D.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".
D.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".
o Remove the Appendix B "Codepoints which need special mapping" and
mentioned related documents in the Section 2.2 .
D.3. Changes since -02
o Removed the "Open issues".
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D.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.
D.5. Changes since -04
o Correct a sentence in the Section 2.3 "Local case mapping".
D.6. Changes since -05
o Correct some sentences in this document.
o Modify the local case mapping's rule and target characters in
Section 2.3 "Local case mapping". This is to avoid user's
confusion towards Greek's final sigma and German's eszett.
o Add the Section 4 "Open issues".
o Modify the Section 8 "Security Considerations".
o Modify the table format in the Appendix A. "Mapping type list
each protocol".
o Removed the Appendix B "Code points list for local case mapping".
o Add the Appendix B "Local case mapping vs Case mapping".
D.7. Changes since -06
o Removed the Section 4 "Open issues".
o Change the title of the Appendix B "Local case mapping vs Case
mapping" to "The reason why local case mapping is alternative to
case mapping in PRECIS framework".
o Add the Appendix C "Limitation to local case mapping".
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D.8. Changes since -07
o Modify the Section 1 "Introduction".
o Modify the local case mapping's rule and target characters in
Section 2.3 "Local case mapping".
o Modify the Section 3 "Order of operations".
D.9. Changes since -08
o Updated the Unicode version 6.3 to 7.0 in this document.
D.10. Changes since -09
o Modify the Section 1 "Introduction" to clarify to the discussion
of string matching and the use of mappings from the
SpecialCasing.txt.
o Modify the Section 2.3 "Local case mapping" to clarify to the
discussion of string matching and the use of mappings from the
SpecialCasing.txt.
o Modify the Appendix B "The reason why local case mapping is
alternative to case mapping in PRECIS framework" to state the
result of the case mapping in SpecialCasing.txt of eszett.
o Clarify the Appendix C "Limitation to local case mapping".
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
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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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