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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 4790

Network Working Group                                          C. Newman
Internet-Draft                                          Sun Microsystems
Expires: January 13, 2005                                  July 15, 2004


            Internet Application Protocol Collation Registry
                  draft-newman-i18n-comparator-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 13, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   Many Internet application protocols include string-based lookup,
   searching, or sorting operations.  However the problem space for
   searching and sorting international strings is large, not fully
   explored, and is outside the area of expertise for the Internet
   Engineering Task Force (IETF).  Rather than attempt to solve such a
   large problem, this specification creates an abstraction framework so
   that application protocols can precisely identify a comparison
   function and the repertoire of comparison functions can be extended
   in the future.






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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1  Conventions Used in this Document  . . . . . . . . . . . .   3
   2.   Collation Definition and Purpose . . . . . . . . . . . . . .   3
   3.   Collation Name Syntax  . . . . . . . . . . . . . . . . . . .   4
   4.   Collation Specification Requirements . . . . . . . . . . . .   6
   5.   Application Protocol Requirements  . . . . . . . . . . . . .   8
   6.   Initial Collations . . . . . . . . . . . . . . . . . . . . .   9
     6.1  Octet Collation  . . . . . . . . . . . . . . . . . . . . .   9
     6.2  ASCII Numeric Collation  . . . . . . . . . . . . . . . . .  10
     6.3  ASCII Casemap Collation  . . . . . . . . . . . . . . . . .  10
     6.4  Nameprep Collation . . . . . . . . . . . . . . . . . . . .  10
     6.5  Basic Collation  . . . . . . . . . . . . . . . . . . . . .  11
   7.   Use by ACAP and Sieve  . . . . . . . . . . . . . . . . . . .  13
   8.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  13
     8.1  Collation Registration Procedure . . . . . . . . . . . . .  13
     8.2  Collation Registration Template  . . . . . . . . . . . . .  14
     8.3  Octet Collation Registration . . . . . . . . . . . . . . .  15
     8.4  ASCII Numeric Collation Registration . . . . . . . . . . .  16
     8.5  Legacy English Casemap Collation Registration  . . . . . .  16
     8.6  English Casemap Collation Registration . . . . . . . . . .  16
     8.7  Nameprep Collation Registration  . . . . . . . . . . . . .  17
     8.8  Basic Collation Registration . . . . . . . . . . . . . . .  17
     8.9  Basic Accent Sensitive Match Collation Registration  . . .  18
     8.10   Basic Case Sensitive Match Collation Registration  . . .  18
     8.11   Structure of Collation Registry  . . . . . . . . . . . .  18
     8.12   Example Initial Registry Summary . . . . . . . . . . . .  19
   9.   DTD for Collation Registration . . . . . . . . . . . . . . .  19
   10.  Guidelines for Expert Reviewer . . . . . . . . . . . . . . .  20
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .  21
   12.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . .  21
   13.  Changes From -01 . . . . . . . . . . . . . . . . . . . . . .  22
   14.  Changes From -00 . . . . . . . . . . . . . . . . . . . . . .  22
   15.  References . . . . . . . . . . . . . . . . . . . . . . . . .  22
   15.1   Normative References . . . . . . . . . . . . . . . . . . .  22
   15.2   Informative References . . . . . . . . . . . . . . . . . .  23
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  23
        Intellectual Property and Copyright Statements . . . . . . .  24












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1.  Introduction

   The ACAP [11] specification introduced the concept of a comparator
   (which we call collation in this document), but failed to create an
   IANA registry.  With the introduction of stringprep [6] and the
   Unicode Collation Algorithm [8], it is now time to create that
   registry and populate it with some initial values appropriate for an
   international community.  This specification replaces and generalizes
   the definition of a comparator in ACAP and creates a collation
   registry.

1.1  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [1].

   The attribute syntax specifications use the Augmented Backus-Naur
   Form (ABNF) [2] notation including the core rules defined in Appendix
   A.  This also inherits ABNF rules from Language Tags [5].

2.  Collation Definition and Purpose

   A collation is a named function which takes two arbitrary length
   octet strings (encoded in UTF-8 [3] for collations which operate on
   characters) as input and can be used to perform one or more of three
   basic comparison operations: equality test, substring match and
   ordering test.

   Collations provide a multi-protocol abstraction layer for comparison
   functions so the details of a particular comparison operation can be
   specified by someone with appropriate expertise independent of the
   application protocol that consumes that collation.  This is similar
   to the way a charset [14] separates the details of octet to character
   mapping from a protocol specification such as MIME [9] or the way
   SASL [10] separates the details of an authentication mechanism from a
   protocol specification such as ACAP [11].














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   Here a small diagram to help illustrate the value of this abstraction
   layer:

                                                 +-----------------+
                                                 | Octet           |
   +-------------------+                      +--| Collation Spec  |
   | IMAP i18n SEARCH  |--+                   |  +-----------------+
   +-------------------+  |  +-------------+  |  +-----------------+
                          +--| Collation   |--+--| A stringprep    |
   +-------------------+  |  | Registry    |  |  | Collation Spec  |
   | ACAP i18n SEARCH  |--+  +-------------+  |  +-----------------+
   +-------------------+                      |  +-----------------+
                                              |  | locale-specific |
                                              +--| Collation Spec  |
                                                 +-----------------+

   Thus IMAP, ACAP and future application protocols with international
   search capability simply specify how to interface to the collation
   registry instead of each protocol spec having to specify all the
   collations it supports.

   One component of a collation is a canonicalization function which can
   be pre-applied to single strings and may enhance the performance of
   subsequent comparison operations.  Normally, this is an
   implementation detail of collations, but at times it may be useful
   for an application protocol to expose collation canonicalization over
   protocol.  Collation canonicalization can range from an identity
   mapping (e.g., the i;octet collation) to a mapping which makes the
   string unreadable to a human (e.g., the basic collation).

3.  Collation Name Syntax

   The collation name itself is a single US-ASCII string beginning with
   a letter and made up of letters, digits, or one of the following 4
   symbols: "-", ";", "=" or ".".  The name MUST NOT be longer than 254
   characters.

     collation-char  =  ALPHA / DIGIT / "-" / ";" / "=" / "."

     collation-name  =  ALPHA *253collation-char

   The string a client uses to select a collation MAY contain a wildcard
   ("*") character which matches zero or more collation-chars.  Wildcard
   characters MUST NOT be adjacent.  Clients which support disconnected
   operation SHOULD NOT use wildcards to select a collation, but clients
   which provide collation operations only when connected to the server
   MAY use wildcards.  If the wildcard string matches multiple
   collations, the server SHOULD select the collation with the broadest



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   scope (preferably international scope), the most recent table
   versions and the greatest number of supported operations.  A single
   wildcard character ("*") refers to the application protocol collation
   behavior that would occur if no explicit negotiation were used.

   When used as a protocol element for ordering, the collation name MAY
   be prefixed by either "+" or "-" to explicitly specify an ordering
   direction.  As mentioned previously, "+" has no effect on the
   ordering function, while "-" negates the result of the ordering
   function.  In general, collation-order is used when a client requests
   a collation, and collation-sel is used with the server informs the
   client of the selected collation.

     collation-wild  =  ("*" / (ALPHA ["*"])) *(collation-char ["*"])
                         ; MUST NOT exceed 255 characters total

     collation-sel   =  ["+" / "-"] collation-name

     collation-order =  ["+" / "-"] collation-wild

   Some protocols are designed to use URIs to refer to collations rather
   than simple tokens.  A special section of the IANA web page is
   reserved for such usage.  The "collation-uri" form is used to refer
   to a specific IANA registry entry for a specific named collation (the
   collation registration may not actually be present if it is
   experimental).  The "collation-auri" form is an abstract name for an
   ordering, a comparator pattern or a vendor private comparator.

     collation-uri   =  "http://www.iana.org/assignments/collation/"
                        collation-name ".xml"

     collation-auri  =  ( "http://www.iana.org/assignments/collation/"
                        collation-order [".xml"]) / other-uri

     other-uri       =  absoluteURI
                     ;  excluding the IANA collation namespace.

   While this specification makes no absolute requirements on the
   structure of collation names, naming consistency is important, so the
   following initial guidelines are provided.

   Collation names with an international audience typically begin with
   "i;".  Collation names intended for a particular language or locale
   typically begin with a language tag [5] followed by a ";".  After the
   first ";" is normally the name of the general collation algorithm
   followed by a series of algorithm modifications separated by the ";"
   delimiter.  Parameterized modifications will use "=" to delimit the
   parameter from the value.  The version numbers of any lookup tables



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   used by the algorithm SHOULD be present as parameterized
   modifications.

   Collation names of the form *;vnd-domain.com;* are reserved for
   vendor-specific collations created by the owner of the domain name
   following the "vnd-" prefix.  Registration of such collations (or the
   name space as a whole) with intended use of "Vendor" is encouraged
   when a public specification or open-source implementation is
   available, but is not required.

4.  Collation Specification Requirements

   A collation specification MUST state which of the three basic
   functions are supported (equality, substring, ordering) and how to
   perform each of the supported functions on any two input
   octet-strings including empty strings.  Given a collation with a
   specific name, and any two fixed input strings, the result MUST be
   the same.  The collation specification MUST state whether the
   collation operates on raw octets or on characters (in which case the
   UTF-8 charset is presumed).  Collations MUST be transitive.

   A collation specification MUST describe the internal canonicalization
   algorithm.  This algorithm can be applied to individual strings and
   the result strings can be stored to potentially optimize future
   comparison operations.  A collation MAY specify that the
   canonicalization algorithm is the identity function.  The output of
   the canonicalization algorithm MAY have no meaning to a human.

   Collations which use more than one customizable lookup table in a
   documented format MUST assign numbers to the tables they use.  This
   permits an application protocol command to access the tables used by
   a server collation.
   o  The equality function always returns "match" or "no-match" when
      supplied valid input and MAY return "error" if the input strings
      are not valid UTF-8 strings or violate other collation
      constraints.
   o  The substring matching function determines if the first string is
      a substring of the second string.  A collation which supports
      substring matching will automatically support the two special
      cases of substring matching: prefix and suffix matching if those
      special cases are supported by the application protocol.  It
      returns "match" or "no-match" when supplied valid input and
      returns "error" when supplied invalid input.
   o  The ordering function determines how two octet strings are
      ordered.  It returns "-1" if the first string is listed before the
      second string according to the collation, "+1" if the second
      string is listed before the first string, and "0" if the two
      strings are equal.  If the order of the two strings is reversed,



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      the result of the ordering function of the collation MUST be
      negated.  In general, collations SHOULD NOT return "0" unless the
      two octet sequences are identical.

      Since ordering is normally used to sort a list of items, "error"
      is not a useful return value from the ordering function.  Strings
      with errors that prevent the sorting algorithm from functioning
      correctly should sort to the end of the list.  Thus if the first
      string is invalid UTF-8 while the second string is valid, the
      result will be "+1".  If the second string is invalid UTF-8 while
      the first string is valid, the result will be "-1".  If the
      collation is character-based, and both strings are invalid UTF-8,
      the result SHOULD match the result from the "i;octet" collation.

      When the collation is used with a "+" prefix, the behavior is the
      same as when used with no prefix.  When the collation is used with
      a "-" prefix, results which would be "+1" are instead "-1" and
      results which would be "-1" are instead "+1".

   Unless otherwise specified by the collation or application protocol,
   a NULL string (as opposed to an empty string) is equal only to
   another NULL string, a NULL string is not a substring of any other
   string, and a NULL string sorts to a position after all non-NULL
   strings, but before strings which generate errors.

   Some application protocols will permit the use of multi-value
   attributes with a collation.  This paragraph describes the rules that
   apply unless otherwise specified by the collation or application
   protocol.  The equality and substring collation algorithms will be
   iterated over each pair of single values from the two inputs.  If any
   combination produces an error, the result is an error.  Otherwise, if
   any combination produces a "match", the result is a match.  Otherwise
   the result is "no-match".  For the ordering function, the smallest
   ordinal octet string from the first set of values is compared to the
   smallest ordinal octet string from the second set of values.

   Application protocols MAY return position information for substring
   matches.  If this is done, the position information MUST include both
   the starting offset and the ending offset in the string.  This is
   important because more sophisticated collations can match strings of
   unequal length (for example, a pre-composed accented character will
   match a decomposed accented character).

   Collation specifications intended for common use are expected to
   reference standards from standards bodies with significant experience
   dealing with the details of international character sets.





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5.  Application Protocol Requirements

   An application protocol which offers searching, substring matching
   and/or sorting and permits the use of characters outside the US-ASCII
   charset needs to consider the following requirements and issues:

   The protocol MUST provide a mechanism for the client to select the
   collation to use with equality matching, substring matching and
   ordering.

   The protocol MUST specify how comparisons behave in the absence of an
   explicit collation negotiation or when a collation negotiation of "*"
   is used.  The protocol MAY specify that the default collation used in
   such circumstances is sensitive to server configuration.

   The protocol SHOULD provide a way to list available collations
   matching a given wildcard pattern or patterns.

   If the protocol provides positional information for the results of a
   substring match, that positional information MUST fully specify the
   substring in the result that matches independent of the length of the
   search string.  For example, returning both the starting and ending
   offset of the match would suffice, as would the starting offset and a
   length.  Returning just the starting offset is not acceptable.  This
   rule is necessary because advanced collations can treat strings of
   different lengths as equal (for example, pre-composed and decomposed
   accented characters).

   If the protocol permits the use of collations on stored character
   data which is not encoded with the UTF-8 charset, then the protocol
   specification has to describe relevant issues of the conversion.
   Details to consider include how to handle unknown charsets, any
   charsets which are mandatory-to-implement, any issues with byte-order
   that might apply, and any transfer encodings which need to be
   supported.

   If the protocol provides a canonicalization function for strings,
   then use of collations MAY be appropriate for that function.

   If the protocol supports disconnected clients, then a mechanism for
   the client to precisely replicate the server's collation algorithm is
   likely desirable.  Thus the protocol MAY wish to provide a command to
   fetch lookup tables used by charset conversions and collations.

   The protocol specification should consider assigning protocol error
   codes for the following circumstances:
   o  The client requests the use of a collation by name or pattern, but
      no implemented collation matches that pattern.



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   o  The client attempts to use a collation for a function that is not
      supported by that collation.  For example, attempting to use the
      "i;ascii-numeric" collation for a substring matching function.
   o  The client uses an equality or substring matching collation and
      the result is an error.  It may be appropriate to distinguish
      between the two input strings, particularly when one is supplied
      by the client and one is stored by the server.  It might also be
      appropriate to distinguish the specific case of an invalid UTF-8
      string.

   If the protocol permits the use of a collation with data structures
   beyond those described in this specification (octet strings, NULL
   string, array of octet strings), the protocol MUST describe the
   default behavior for a collation with that data structure.

6.  Initial Collations

   This section describes an initial set of collations for the collation
   registry.

6.1  Octet Collation

   The "i;octet" collation is a simple and fast collation intended for
   use on binary octet strings rather than on character data.  It never
   returns an "error" result.  It provides equality, substring and
   ordering functions.  The ordering algorithm is as follows:
   1.  If both strings are the empty string, return the result "0".
   2.  If the first string is empty and the second is not, return the
       result "-1".
   3.  If the second string is empty and the first is not, return the
       result "+1".
   4.  If both strings begin with the same octet value, remove the first
       octet from both strings and repeat this algorithm from step 1.
   5.  If the unsigned value (0 to 255) of the first octet of the first
       string is less than the unsigned value of the first octet of the
       second string, then return "-1".
   6.  If this step is reached, return "+1".

   This algorithm is roughly equivalent to the C library function memcmp
   with appropriate length checks added.

   The matching function returns "match" if the sorting algorithm would
   return "0".  Otherwise the matching function returns "no-match".

   The substring function returns "match" if the first string is the
   empty string, or if there exists a substring of the second string of
   length equal to the length of the first string which would result in
   a "match" result from the equality function.  Otherwise the substring



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   function returns "no-match".

   The associated canonicalization algorithm is the identity function.

6.2  ASCII Numeric Collation

   The "i;ascii-numeric" collation is a simple collation intended for
   use with arbitrary sized decimal numbers stored as octet strings of
   US-ASCII digits (0x30 to 0x39).  It supports equality and ordering,
   but does not support the substring function.  The algorithm is as
   follows:
   1.  If neither string begins with a digit, return "error" if
       matching, or the result of the "i;octet" collation for ordering.
   2.  If the first string begins with a digit and the second string
       does not, return "error" if matching and "-1" for ordering.
   3.  If the second string begins with a digit and the first string
       does not, return "error" if matching and "+1" for ordering.
   4.  Let "n" be the number of digits at the beginning of the first
       string, and "m" be the number of digits at the beginning of the
       second string.
   5.  If n is equal to m, return the result of the "i;octet" collation.
   6.  If n is greater than m, prepend a string of "n - m" zeros to the
       second string and return the result of the "i;octet" collation.
   7.  If m is greater than n, prepend a string of "m - n" zeros to the
       first string and return the result of the "i;octet" collation.

   The associated canonicalization algorithm is to truncate the input
   string at the first non-digit character.

6.3  ASCII Casemap Collation

   The "en;ascii-casemap" collation is a simple collation intended for
   use with English language text in pure US-ASCII.  It provides
   equality, substring and ordering functions.  The algorithm first
   applies a canonicalization algorithm to both input strings which
   subtracts 32 (0x20) from all octet values between 97 (0x61) and 122
   (0x7A) inclusive.  The result of the collation is then the same as
   the result of the "i;octet" collation for the canonicalized strings.
   Care should be taken when using OS-supplied functions to implement
   this collation as this is not locale sensitive, but functions such as
   strcasecmp and toupper can be locale sensitive.

   For historical reasons, in the context of ACAP and Sieve, the name
   "i;ascii-casemap" is a synonym for this collation.

6.4  Nameprep Collation

   The "i;nameprep;v=1;uv=3.2" collation is an implementation of the



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   nameprep [7] specification based on normalization tables from Unicode
   version 3.2.  This collation applies the nameprep canoncialization
   function to both input strings and then returns the result of the
   i;octet collation on the canonicalized strings.  While this collation
   offers all three functions, the ordering function it provides is
   inadequate for use by the majority of the world.

   Version number 1 is applied to nameprep as specified in RFC 3491.  If
   the nameprep specification is revised without any changes that would
   produce different results when given the same pair of input octet
   strings, then the version number will remain unchanged.

   The table numbers for tables used by nameprep are as follows:

                +--------------+-----------------------+
                | Table Number | Table Name            |
                +--------------+-----------------------+
                |            1 | UnicodeData-3.2.0.txt |
                |            2 | Table B.1             |
                |            3 | Table B.2             |
                |            4 | Table C.1.2           |
                |            5 | Table C.2.2           |
                |            6 | Table C.3             |
                |            7 | Table C.4             |
                |            8 | Table C.5             |
                |            9 | Table C.6             |
                |           10 | Table C.7             |
                |           11 | Table C.8             |
                |           12 | Table C.9             |
                +--------------+-----------------------+


6.5  Basic Collation

   The basic collation is intended to provide tolerable results for a
   number of languages for all three functions (equality, substring and
   ordering) so it is suitable as a mandatory-to-implement collation for
   protocols which include ordering support.  The ordering function of
   the basic collation is the Unicode Collation Algorithm [8] version 9
   (UCAv9).

   The equality and substring functions are created as described in
   UCAv9 section 8.  While that section is informative to UCAv9, it is
   normative to this collation specification.

   This collation is based on Unicode version 3.2, with the following
   tables relevant:




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   1.  For the normalization step,
       <http://www.unicode.org/Public/3.2-Update/UnicodeData-3.2.0.txt>
       is used.  Column 5 is used to determine the canonical
       decomposition, while column 3 contains the canonical combining
       classes necessary to attain canonical order.
   2.  The table of characters which require a logical order exception
       is a subset of the table in
       <http://www.unicode.org/Public/3.2-Update/PropList-3.2.0.txt> and
       is included here:

   0E40..0E44    ; Logical_Order_Exception
   # Lo   [5] THAI CHARACTER SARA E..THAI CHARACTER SARA AI MAIMALAI
   0EC0..0EC4    ; Logical_Order_Exception
   # Lo   [5] LAO VOWEL SIGN E..LAO VOWEL SIGN AI

   # Total code points: 10

   3.  The table used to translate normalized code points to a sort key
       is <http://www.unicode.org/reports/tr10/allkeys-3.1.1.txt>.

   UCAv9 includes a number of configurable parameters and steps labelled
   as potentially optional.  The following list summarizes the defaults
   used by this collation:
   o  The logical order exception step is mandatory by default to
      support the largest number of languages.
   o  Steps 2.1.1 to 2.1.3 are mandatory as the repertoire of the basic
      collation is intended to be large.
   o  The second level in the sort key is evaluated forwards by default.
   o  The variable weighting uses the "non-ignorable" option by default.
   o  The semi-stable option is not used by default.
   o  Support for exactly three levels of collation is the default
      behavior.
   o  No preprocessing step is used by the basic collation prior to
      applying the UCAv9 algorithm.  Note that an application protocol
      specification MAY require pre-processing prior to the use of any
      collations.
   o  The equality and substring algorithms exclude differences at level
      2 and 3 by default (thus it is case-insensitive and ignores
      accentual distinctions.
   o  The equality and substring algorithms use the "Whole Characters
      Only" feature described in UCAv9 section 8 by default.

   The exact collation name with these defaults is
   "i;basic;uca=3.1.1;uv=3.2".  When a specification states that the
   basic collation is mandatory-to-implement, only this specific name is
   mandatory-to-implement.





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   In order to allow modification of the optional behaviors, the
   following ABNF is used for variations of the basic collation:

     basic-collation  =  ("i" / Language-Tag) ";basic;uca=3.1.1;uv=3.2"
                         [";match=accent" / ";match=case"]
                         [";tailor=" 1*collation-char ]

   If multiple modifiers appear, they MUST appear in the order described
   above.  The modifiers have the following meanings:
   match=accent   Both the first and second levels of the sort keys are
                  considered relevant to the equality and substring
                  operations (rather than the default of first level
                  only).  This makes the matching functions sensitive to
                  accentual distinctions.
   match=case     The first three levels of sort keys are considered
                  relevant to the equality and substring operations.
                  This makes the matching functions sensitive to both
                  case and accentual distinctions.

   The default weighting option is "non-ignorable".  The "semi-stable"
   sort key option is not used by default.

   The canonicalization algorithm associated with this collation is the
   output of step 3 of the UCAv9 algorithm (described in section 4.3 of
   the UCA specification).  This canonicalization is not suitable for
   human consumption.

   Finally, the UCAv9 algorithm permits the "allkeys" table to be
   tailored to a language.  People who make quality tailorings are
   encouraged to register those tailorings using the collation registry.
   Tailoring names beginning with "x" are reserved for experimental use,
   are treated as "Limited use" and MUST NOT match wildcards if any
   registered collation is available that does match.

7.  Use by ACAP and Sieve

   Both ACAP [11] and Sieve [15] are standards track specifications
   which used collations prior to the creation of this specification and
   registry.  Those standards do not meet all the application protocol
   requirements described in Section 5.  For backwards compatibility,
   those protocols use the "i;ascii-casemap" instead of
   "en;ascii-casemap".

8.  IANA Considerations

8.1  Collation Registration Procedure

   IANA will create a mailing list collation@iana.org which can be used



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   for public discussion of collation proposals prior to registration.
   Use of the mailing list is encouraged but not required.  The actual
   registration procedure will not begin until the completed
   registration template is sent to iana@iana.org.  The IESG will
   appoint a designated expert who will monitor the collation@iana.org
   mailing list and review registrations forwarded from IANA.  The
   designated expert is expected to tell IANA and the submitter of the
   registration within two weeks whether the registration is approved,
   approved with minor changes, or rejected with cause.  When a
   registration is rejected with cause, it can be re-submitted if the
   concerns listed in the cause are addressed.  Decisions made by the
   designated expert can be appealed to the IESG and subsequently follow
   the normal appeals procedure for IESG decisions.

   Collation registrations in a standards track, BCP or IESG-approved
   experimental RFC are owned by the IESG and changes to the
   registration follow normal procedures for updating such documents.
   Collation registrations in other RFCs are owned by the RFC author(s).
   Other collation registrations are owned by the individual(s) listed
   in the contact field of the registration and IANA will preserve this
   information.  Changes to a registration MUST be approved by the
   owner.  In the event the owner can't be contacted for a period of one
   month and a change is deemed necessary, the IESG MAY re-assign
   ownership to an appropriate party.

8.2  Collation Registration Template

   Registration of a collation is done by sending a well-formed XML
   document that validates with collationreg.dtd (Section 9).  The
   registration MUST include a collation element that MAY include an
   "rfc=" attribute if the specification is in an RFC and MUST include a
   scope attribute of "i18n", "local" or "other" and an intendedUse
   attribute of "common", "limited", "vendor", or "deprecated".

   The collation element contains the other elements in the
   registration.  The mandatory name element gives the precise name of
   the comparator.  The mandatory title element give the title of the
   comparator.  The mandatory functions element lists which of the three
   functions the comparator provides.  The mandatory specification
   element describes where to find the specification, and MAY have a URI
   attribute.  The submittor element provides an RFC 2822 email address
   for the person who submitted the registration.  It is optional if the
   owner element contains an email address.  The mandatory owner element
   contains either the four letters "IETF" or an email address of the
   owner of the registration.  The optional version element is included
   when the registration is likely to be revised or has been revised in
   such a way that the results change for certain input strings.  The
   optional UnicodeVersion element indicates the version number of the



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   UnicodeData file on which the collation is based.  The optional
   UCAVersion element specifics the version of the Unicode Collation
   Algorithm on which the collation is based.  The optional
   UCAMatchLevel element specifies the number of Unicode Collation
   Algorithm sort key levels used for the equality and substring
   operations.

   Here is a template for the registration:

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>collation name</name>
     <title>technical title for collation</title>
     <functions>equality order substring</functions>
     <specification>specification reference</specification>
     <owner>email address of owner or IETF</owner>
     <submittor>email address of submittor<submittor>
     <version>1</version>
     <UnicodeVersion>3.2</UnicodeVersion>
     <UCAVersion>3.1.1</UCAVersion>
   </collation>

   Be aware that future revisions of this specification may add
   additional function types, as well as additional XML attributes and
   values.  Any system which automatically parses these XML documents
   MUST take this into account to preserve future compatibility.

8.3  Octet Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>i;octet</name>
     <title>Octet</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
   </collation>











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8.4  ASCII Numeric Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="other" intendedUse="limited">
     <name>i;ascii-numeric</name>
     <title>ASCII Numeric</title>
     <functions>equality order</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
   </collation>


8.5  Legacy English Casemap Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="local" intendedUse="deprecated">
     <name>i;ascii-casemap</name>
     <title>Legacy English Casemap</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
   </collation>


8.6  English Casemap Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="local" intendedUse="common">
     <name>en;ascii-casemap</name>
     <title>English Casemap</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
   </collation>











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8.7  Nameprep Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>i;nameprep;v=1;uv=3.2</name>
     <title>Nameprep</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
     <version>1</version>
     <UnicodeVersion>3.2</UnicodeVersion>
   </collation>


8.8  Basic Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>i;basic;uca=3.1.1;uv=3.2</name>
     <title>Basic</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
     <UnicodeVersion>3.2</UnicodeVersion>
     <UCAVersion>3.1.1</UCAVersion>
     <UCAMatchLevel>1</UCAMatchLevel>
   </collation>




















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8.9  Basic Accent Sensitive Match Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>i;basic;uca=3.1.1;uv=3.2;match=accent</name>
     <title>Basic Accent Sensitive Match</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
     <UnicodeVersion>3.2</UnicodeVersion>
     <UCAVersion>3.1.1</UCAVersion>
     <UCAMatchLevel>2</UCAMatchLevel>
   </collation>


8.10  Basic Case Sensitive Match Collation Registration

   <?xml verison='1.0'?>
   <!DOCTYPE rfc SYSTEM 'collationreg.dtd'>
   <collation rfc="XXXX" scope="i18n" intendedUse="common">
     <name>i;basic;uca=3.1.1;uv=3.2;match=case</name>
     <title>Basic Case Sensitive Match</title>
     <functions>equality order substring</functions>
     <specification>RFC XXXX</specification>
     <owner>IETF</owner>
     <submittor>chris.newman@sun.com<submittor>
     <UnicodeVersion>3.2</UnicodeVersion>
     <UCAVersion>3.1.1</UCAVersion>
     <UCAMatchLevel>3</UCAMatchLevel>
   </collation>


8.11  Structure of Collation Registry

   Once the registration is approved, IANA will store each XML
   registration document in a URL of the form
   http://www.iana.org/assignments/collation/collation-name.xml where
   collation-name is the contents of the name element in the
   registration.  Both the submittor and the designated expert is
   responsible for verifying that the XML is well-formed and complies
   with the DTD.  In the future, it is hoped IANA will take over XML
   verification responsibility from the designated expert.

   IANA will also maintain a text summary of the registry under the name
   http://www.iana.org/assignments/collation/summary.txt.  This summary
   is divided into four sections.  The first section is for collations



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   intended for common use.  This section is intended for collation
   registrations published in IESG approved RFCs or for locally scoped
   collations from the primary standards body for that locale.  The
   designated expert is encouraged to reject collation registrations
   with an intended use of "common" if the expert believes it should be
   "limited", as it is desirable to keep the number of "common"
   registrations small and high quality.  The second section is reserved
   for limited use collations.  The third section is reserved for
   registered vendor specific collations.  The final section is reserved
   for deprecated collations.

8.12  Example Initial Registry Summary

   The following is an example of how IANA might structure the initial
   registry summary.txt file:

     Collation                              Functions Scope Reference
     ---------                              --------- ----- ---------
   Common Use Collations:
     i;octet                                e, o, s   Other [RFC XXXX]
     i;nameprep;v=1;uv=3.2                  e, o, s   i18n  [RFC XXXX]
     i;basic;uca=3.1.1;uv=3.2               e, o, s   i18n  [RFC XXXX]
     i;basic;uca=3.1.1;uv=3.2;match=accent  e, o, s   i18n  [RFC XXXX]
     i;basic;uca=3.1.1;uv=3.2;match=case    e, o, s   i18n  [RFC XXXX]
     en;ascii-casemap                       e, o, s   Local [RFC XXXX]

   Limited Use Collations:
     i;ascii-numeric                        e, o      Other [RFC XXXX]

   Vendor Collations:

   Deprecated Collations:
     i;ascii-casemap                        e, o, s   Local [RFC XXXX]


   References
   ----------
   [RFC XXXX]  Newman, C., "Internet Application Protocol Collation
               Registry", RFC XXXX, Sun Microsystems, October 2003.


9.  DTD for Collation Registration









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   <!-
     DTD for Collation Registration Document

     Data types:

     entity      description
     ======      ===========
     NUMBER      [0-9]+
     URI         As defined in RFC 2396
     CTEXT       printable ASCII text (no line-terminators)
     TEXT        character data
     ->
   <!ENTITY % NUMBER        "CDATA">
   <!ENTITY % URI           "CDATA">
   <!ENTITY % CTEXT         "#PCDATA">
   <!ENTITY % TEXT          "#PCDATA">
   <!ELEMENT collation      (name,title,functions,specification+,owner+,
                             submittor*,version?,UnicodeVersion?,
                             UCAVersion?,UCAMatchLevel?)>
   <!ATTLIST collation
             rfc            %NUMBER;                           "0"
             scope          (i18n|local|other)                 #IMPLIED
             intendedUse    (common|limited|vendor|deprecated) #IMPLIED>
   <!ELEMENT name           (%CTEXT;)>
   <!ELEMENT title          (%CTEXT;)>
   <!ELEMENT functions      (%CTEXT;)>
   <!ELEMENT specification  (%TEXT;)>
   <!ATTLIST specification
             uri            %URI;                              "">
   <!ELEMENT owner          (%CTEXT;)>
   <!ELEMENT submittor      (%CTEXT;)>
   <!ELEMENT version        (%CTEXT;)>
   <!ELEMENT UnicodeVersion (%CTEXT;)>
   <!ELEMENT UCAVersion     (%CTEXT;)>
   <!ELEMENT UCAMatchLevel  (%CTEXT;)>


10.  Guidelines for Expert Reviewer

   The expert reviewer appointed by the IESG has fairly broad latitude
   for this registry.  While a number of collations are expected
   (particularly customizations of the basic collation for localized
   use), an explosion of collations (particularly common use collations)
   is not desirable for widespread interoperability.  However, it is
   important for the expert reviewer to provide cause when rejecting a
   registration, and when possible to describe corrective action to
   permit the registration to proceed.  The following table includes
   some example reasons to reject a registration with cause:



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   o  The registration is not a well-formed XML document that follows
      the DTD.
   o  The registration has intended use of "common", but there is no
      evidence the collation will be widely deployed so it should be
      listed as "limited".
   o  The registration has intended use of "common", but is redundant
      with the functionality of a previously registered "common"
      collation.
   o  The collation name fails to precisely identify the version numbers
      of relevant tables to use.
   o  The registration fails to meet one of the "MUST" requirements in
      Section 4.
   o  The collation name fails to meet the syntax in Section 3.
   o  The collation specification referenced in the registration is
      vague or has optional features without a clear behavior specified.
   o  The referenced specification does not adequately address security
      considerations specific to that collation.

11.  Security Considerations

   Collations will normally be used with UTF-8 strings.  Thus the
   security considerations for UTF-8 [3] and stringprep [6] also apply
   and are normative to this specification.

12.  Open Issues

   1.  Is any Nameprep processing appropriate for the basic collation?
       Because a result of "0" from an ordering algorithm is
       undesirable, much of the nameprep processing is inappropriate.
       Furthermore, a result of "error" which is important for nameprep
       is generally inappropriate as an internal result in an ordering
       algorithm since it makes the results less intuitive.  The sort
       key table also eliminates most problematic characters from
       consideration if the appropriate collation modifier is used.
       Finally, exact compatibility with the Unicode Collation Algorithm
       is deemed desirable by the author, as even the smallest variation
       may require implementation of largely duplicate code.  However,
       this decision is outside my expertise, so I welcome alternate
       viewpoints.
   2.  The ICU implementation of the UCA algorithm includes additional
       algorithmic customizations such as the ability to be
       case-sensitive while at the same time being insensitive to
       accents.  Should these customizations be added to this
       specification?
   3.  Should a format for customization data for the basic collation be
       defined so that disconnected clients might have the option of
       downloading that information?




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   4.  Need to deal with the concept of "maybe" or "indeterminate"
       results from matching or ordering.  See what LDAP does as an
       example.
   5.  Need to get agreement from IANA to provide persistent URLs (URNs
       are not sufficient) for the collation registry.

13.  Changes From -01

   Add IANA comment to open issues.  Otherwise this is just a re-publish
   to keep the document alive.

14.  Changes From -00

   1.  Replaced the term comparator with collation.  While comparator is
       somewhat more precise because these abstract functions are used
       for matching as well as ordering, collation is the term used by
       other parts of the industry.  Thus I have changed the name to
       collation for consistency.
   2.  Remove all modifiers to the basic collation except for the
       customization and the match rules.  The other behavior
       modifications can be specified in a customization of the
       collation.
   3.  Use ";" instead of "-" as delimiter between parameters to make
       names more URL-ish.
   4.  Add URL form for comparator reference.
   5.  Switched registration template to use XML document.
   6.  Added a number of useful registration template elements related
       to the Unicode Collation Algorithm.
   7.  Switched language from "custom" to "tailor" to match UCA language
       for tailoring of the collation algorithm.

15.  References

15.1  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [3]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
        2279, January 1998.

   [4]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
        Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

   [5]  Alvestrand, H., "Tags for the Identification of Languages", BCP



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        47, RFC 3066, January 2001.

   [6]  Hoffman, P. and M. Blanchet, "Preparation of Internationalized
        Strings ("stringprep")", RFC 3454, December 2002.

   [7]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for
        Internationalized Domain Names (IDN)", RFC 3491, March 2003.

   [8]  Davis, M. and K. Whistler, "Unicode Collation Algorithm version
        9", July 2002,
        <http://www.unicode.org/reports/tr10/tr10-9.html>.

15.2  Informative References

   [9]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message Bodies",
         RFC 2045, November 1996.

   [10]  Myers, J., "Simple Authentication and Security Layer (SASL)",
         RFC 2222, October 1997.

   [11]  Newman, C. and J. Myers, "ACAP -- Application Configuration
         Access Protocol", RFC 2244, November 1997.

   [12]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434, October
         1998.

   [13]  Resnick, P., "Internet Message Format", RFC 2822, April 2001.

   [14]  Freed, N. and J. Postel, "IANA Charset Registration
         Procedures", BCP 19, RFC 2978, October 2000.

   [15]  Showalter, T., "Sieve: A Mail Filtering Language", RFC 3028,
         January 2001.


Author's Address

   Chris Newman
   Sun Microsystems
   1050 Lakes Drive
   West Covina, CA  91790
   US

   EMail: chris.newman@sun.com





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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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