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Versions: (draft-yoneya-precis-mappings) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7790

Network Working Group                                          Y. YONEYA
Internet-Draft                                                      JPRS
Intended status: Informational                                 T. Nemoto
Expires: May 4, 2016                                     Keio University
                                                        November 1, 2015


                 Mapping characters for PRECIS classes
                     draft-ietf-precis-mappings-12

Abstract

   The framework for preparation, enforcement, and comparison of
   internationalized strings ("PRECIS") defines several classes of
   strings for use in application protocols.  Because many protocols
   perform case-sensitive or case-insensitive string comparison, it
   necessary to define methods for case mapping.  In addition, both the
   Internationalized Domain Names in Applications (IDNA) and the PRECIS
   problem statement describe mappings for internationalized strings
   that are not limited to case, but include width mapping and mapping
   of delimiters and other special characters that can be taken into
   consideration.  This document provides guidelines for designers of
   PRECIS profiles and describes several mappings that can be applied
   between receiving user input and passing permitted code points to
   internationalized protocols.  In particular, this document describes
   both locale-dependent and context-depending case mappings as well as
   additional mappings for delimiters and special characters.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 4, 2016.







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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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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 . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Mapping type list each protocol  . . . . . . . . . .   8
     A.1.  Mapping type list for each protocol . . . . . . . . . . .   8
   Appendix B.  The reason why local case mapping is alternative to
                case mapping in PRECIS framework . . . . . . . . . .   8
   Appendix C.  Limitation to local case mapping . . . . . . . . . .   9
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . .   9
     D.1.  Changes since -00 . . . . . . . . . . . . . . . . . . . .   9
     D.2.  Changes since -01 . . . . . . . . . . . . . . . . . . . .   9
     D.3.  Changes since -02 . . . . . . . . . . . . . . . . . . . .  10
     D.4.  Changes since -03 . . . . . . . . . . . . . . . . . . . .  10
     D.5.  Changes since -04 . . . . . . . . . . . . . . . . . . . .  10
     D.6.  Changes since -05 . . . . . . . . . . . . . . . . . . . .  10
     D.7.  Changes since -06 . . . . . . . . . . . . . . . . . . . .  11
     D.8.  Changes since -07 . . . . . . . . . . . . . . . . . . . .  11
     D.9.  Changes since -08 . . . . . . . . . . . . . . . . . . . .  11
     D.10. Changes since -09 . . . . . . . . . . . . . . . . . . . .  11
     D.11. Changes since -10 . . . . . . . . . . . . . . . . . . . .  12
     D.12. Changes since -11 . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13



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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
   [RFC7564].  The case and width mappings defined in the PRECIS
   framework do not handle other mappings such as delimiter characters,
   special characters, and locale-dependent or context-dependent case;
   these mappings 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



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   FULL STOP on the keyboard.  In all these cases, the visually similar
   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 such as CHARACTER TABULATION(U+0009) or IDEOGRAPHIC
      SPACE(U+3000) 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.
   (Note: The term "locale" in this document practically means
   "language" or "language and region" because the locale based on that
   language configuration of applications on POSIX is selected by
   "locale" information and referred "Note" in section 2.1.1 of BCP 47
   [RFC5646].)

   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 language is 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 the PRECIS
   framework does not consider such locale or context because it is a
   common framework for internationalization.  Local case mapping



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   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 the
   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 SpecialCasing.txt
   file.

   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 the
   Section 5.2.3 of the PRECIS framework .  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 a PRECIS profile selects Unicode Default Case Folding as the
   preferred method of case mapping, the profile designers may consider
   whether local case mapping can be applied.  And if it can be applied,
   it is better to add "alternatively, local case mapping might be
   applicable" after "Unicode Default Case Folding" so that application
   developers are aware of the alternative.  See the Appendix B for a
   description of why local case mapping can be an alternative.

3.  Order of operations

   Delimiter mapping and special mapping as described in this document
   are expected to be applied as the "Additional Mapping Rule" mentioned
   in the Section 5.2.2 of the PRECIS framework.  Although the delimited
   mapping and special mapping could be applied in either order, this
   document recommends the following order to minimize the effect of
   code point changes introduced by the mappings and to be acceptable to
   the widest user community:

   1.  Delimiter mapping

   2.  Special mapping

4.  Security Considerations

   Detailed security considerations for PRECIS strings are discussed in
   the PRECIS framework specification [RFC7564].  This document inherits
   the considerations as well.

   As with Mapping Characters for IDNA2008 [RFC5895], this document
   suggests creating mappings that might cause confusion for some users




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   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, 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 working group discussions.

7.  References

7.1.  Normative References

   [RFC7564]  Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
              Preparation, Enforcement, and Comparison of
              Internationalized Strings in Application Protocols",
              RFC 7564, DOI 10.17487/RFC7564, May 2015,
              <http://www.rfc-editor.org/info/rfc7564>.

   [Unicode]  The Unicode Consortium, "The Unicode Standard, Version
              7.0.0",  <http://www.unicode.org/versions/Unicode7.0.0/>,
              2012.

   [Casefolding]
              The Unicode Consortium, "CaseFolding-7.0.0.txt", Unicode
              Character Database, July 2011,
              <http://www.unicode.org/Public/7.0.0/ucd/CaseFolding.txt>.

   [Specialcasing]
              The Unicode Consortium, "SpecialCasing-7.0.0.txt", Unicode
              Character Database, July 2011,
              <http://www.unicode.org/Public/7.0.0/ucd/
              SpecialCasing.txt>.

7.2.  Informative References

   [RFC3454]  Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              DOI 10.17487/RFC3454, December 2002,
              <http://www.rfc-editor.org/info/rfc3454>.



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   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, DOI 10.17487/RFC3490, March 2003,
              <http://www.rfc-editor.org/info/rfc3490>.

   [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, DOI 10.17487/RFC3491, March 2003,
              <http://www.rfc-editor.org/info/rfc3491>.

   [RFC3722]  Bakke, M., "String Profile for Internet Small Computer
              Systems Interface (iSCSI) Names", RFC 3722,
              DOI 10.17487/RFC3722, April 2004,
              <http://www.rfc-editor.org/info/rfc3722>.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <http://www.rfc-editor.org/info/rfc3748>.

   [RFC4013]  Zeilenga, K., "SASLprep: Stringprep Profile for User Names
              and Passwords", RFC 4013, DOI 10.17487/RFC4013, February
              2005, <http://www.rfc-editor.org/info/rfc4013>.

   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, DOI 10.17487/RFC4314, December 2005,
              <http://www.rfc-editor.org/info/rfc4314>.

   [RFC4518]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Internationalized String Preparation", RFC 4518,
              DOI 10.17487/RFC4518, June 2006,
              <http://www.rfc-editor.org/info/rfc4518>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <http://www.rfc-editor.org/info/rfc5646>.

   [RFC5895]  Resnick, P. and P. Hoffman, "Mapping Characters for
              Internationalized Domain Names in Applications (IDNA)
              2008", RFC 5895, DOI 10.17487/RFC5895, September 2010,
              <http://www.rfc-editor.org/info/rfc5895>.

   [RFC6122]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Address Format", RFC 6122,
              DOI 10.17487/RFC6122, March 2011,
              <http://www.rfc-editor.org/info/rfc6122>.





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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,
              DOI 10.17487/RFC6885, March 2013,
              <http://www.rfc-editor.org/info/rfc6885>.

   [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.

   +----------------------+-------------+-----------+------+---------+
   |     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    |
   |   IMAP  (RFC 4314)   |      o      |     -     |   -  |    o    |
   |   LDAP  (RFC 4518)   |      o      |     -     |   o  |    o    |
   +----------------------+-------------+-----------+------+---------+

Appendix B.  The reason why local case mapping is alternative to case
             mapping in PRECIS framework

   Local case mapping is alternative to Unicode Default Case Folding
   instead of being applied sequentially.  Because, one outstanding
   issue regarding full case folding for characters is, some lowercase
   characters like "LATIN SMALL LETTER SHARP S" (U+00DF) (hereinafter
   referred to as "eszett") and ligatures like "LATIN SMALL LIGATURE FF"
   (U+FB00) that described in section Unconditional mappings of
   SpecialCasing.txt become a different codepoint by performing the case
   mapping using Unicode Default Case Folding in the PRECIS framework.
   In particular, German's eszett can not keep the locale because eszett
   becomes two "LATIN SMALL LETTER S"s (U+0073 U+0073) by performing the
   case mapping using Unicode Default Case Folding.  On the other hand,
   eszett doesn't become a different codepoint by performing the case



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   mapping in SpecialCasing.txt.  Therefore, if it is necessary to keep
   locale of characters, PRECIS profile designers should select local
   case mapping as alternative to Unicode Default Case Folding.

Appendix C.  Limitation to local case mapping

   As described in the 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 also 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

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.





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   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".

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 the
      Section 2.3 "Local case mapping".  This is to avoid user's
      confusion towards Greek's final sigma and German's eszett.




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   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".

D.8.  Changes since -07

   o  Modify the Section 1 "Introduction".

   o  Modify the local case mapping's rule and target characters in the
      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.




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   o  Clarify the Appendix C "Limitation to local case mapping".

D.11.  Changes since -10

   o  Modify the "Abstract" to clarify to sentences.

   o  Modify the Section 1 "Introduction" to clarify to a sentence.

   o  Modify the Section 2.2 "Special mapping" to add examples.

   o  Modify the Section 2.3 "Local case mapping" to clarify to
      sentences.  And add a note to explain the term "locale" in this
      document.

   o  Modify the Section 3 "Order of operations" to clarify to
      sentences.

   o  Correct a sentence in the Section 4 "Security Considerations".

   o  Modify a sentence in the Section 6 "Acknowledgment".

   o  Change the references from [I-D.ietf-precis-framework] to
      [RFC7564] in the Section 7 "Normative References".

   o  Removed SASL and XMPP in the table of the Appendix A.  "Mapping
      type list each protocol".

   o  Modify the Appendix B "The reason why local case mapping is
      alternative to case mapping in PRECIS framework" to clarify to
      sentences.

   o  Modify the Appendix C "Limitation to local case mapping" to
      clarify to sentences.

D.12.  Changes since -11

   o  Correct a few sentence in the Section 2.3 "Local case mapping" to
      address comments by the IESG review.

   o  Removed citation part which includes "RECOMMENDED" (RFC 2119 word)
      in the Section 2.3 "Local case mapping" to avoid readers'
      confusion.

   o  Modify the Section 4 "Security Considerations" to add a reference
      to RFC7564.






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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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