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Network Working Group                                          K. Davies
Internet-Draft                                                     ICANN
Intended status: Informational                            March 11, 2012
Expires: September 12, 2012


          Representing registration policy for IDNs using XML
                       draft-davies-idntables-01

Abstract

   This memo describes a method of representing the registration policy
   that a zone administrator uses for registering Internationalised
   Domain Names using Extensible Markup Language (XML).  These registry
   policies, commonly known as "IDN tables", are used to enforce and
   share policy on which specific code-points are permitted for
   registrations, and which alternative code-points are considered
   variants.

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 September 12, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Design Goals . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  IDN Table XML Format . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Namespace  . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Basic structure  . . . . . . . . . . . . . . . . . . . . .  6
     3.3.  The meta element . . . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  The version element  . . . . . . . . . . . . . . . . .  6
       3.3.2.  The date element . . . . . . . . . . . . . . . . . . .  7
       3.3.3.  The language element . . . . . . . . . . . . . . . . .  7
       3.3.4.  The domain element . . . . . . . . . . . . . . . . . .  7
       3.3.5.  The description element  . . . . . . . . . . . . . . .  8
     3.4.  The data element . . . . . . . . . . . . . . . . . . . . .  8
       3.4.1.  Sequences  . . . . . . . . . . . . . . . . . . . . . .  9
       3.4.2.  Variants . . . . . . . . . . . . . . . . . . . . . . .  9
     3.5.  Example table  . . . . . . . . . . . . . . . . . . . . . . 11
   4.  Processing a label against a table . . . . . . . . . . . . . . 12
     4.1.  Determining eligibility for a label  . . . . . . . . . . . 12
     4.2.  Determining variants for a label . . . . . . . . . . . . . 12
   5.  Conversion between other formats . . . . . . . . . . . . . . . 13
     5.1.  RFC 3743 Language Variant Table  . . . . . . . . . . . . . 13
     5.2.  RFC 4290 Model Table Format  . . . . . . . . . . . . . . . 13
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Appendix A.  RelaxNG Schema  . . . . . . . . . . . . . . . . . . . 17
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 20
   Appendix C.  Editorial Notes . . . . . . . . . . . . . . . . . . . 21
     C.1.  Known Issues and Future Work . . . . . . . . . . . . . . . 21
     C.2.  Sample tables and running code . . . . . . . . . . . . . . 21
     C.3.  Change History . . . . . . . . . . . . . . . . . . . . . . 21
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22














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1.  Introduction

   This memo describes how to use Extensible Markup Language (XML) to
   describe the list of permissible code points and variants used in a
   zone administrator's policies.

   Historically, zone administrators - such as top-level domain
   registries - have published their policies using text and HTML based
   formats loosely based around the format used to describe a Language
   Variant Table in [RFC3743].  [RFC4290] further posts a "Model table
   format" that describes a similar set of functionality.

   Through the first decade of IDN deployment, experience has shown that
   these table formats are difficult to consistently implement and
   compare due to their different formats.  A more universal format,
   such as one using a structured XML format, will assist by improving
   machine-readability, consistency, and maintainability of IDN tables.
   It will also provide for more complex conditional implementation of
   variants that reflects the known requirements of current zone
   administrator policies.































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2.  Design Goals

   The following items are explicit design goals of this format:

   o  MUST be in a format that can be implemented in a reasonably
      straightforward manner in software;

   o  The format SHOULD be able to be checked for formatting errors,
      such that common mistakes can be caught;

   o  An IDN Table MUST be able to express the set of valid code points
      that are allowed for registration under a specific zone
      administrator's policies;

   o  MUST be able to express computed alternatives to a given domain
      name based on a one-to-one, or one-to-many relationship.  These
      computed alternatives are commonly known as "IDN variants";

   o  IDN Variants SHOULD be able to be tagged with specific categories,
      such that the categories can be used to support registry policy
      (such as whether to list the computed variant in the zone, or to
      merely block it from registration);

   o  IDN Variants MUST be able to stipulated based on contextual
      information.  For example, specific variants may only be
      applicable when they follow another specific code point, or when
      the code point is displayed in a specific presentation form;

   o  The data contained within the table MUST be unambiguous, such that
      independent implementations that utilise the contents will arrive
      at the same results;

   o  IDN Tables SHOULD be suitable for comparison and re-use, such that
      one could easily compare the contents of two or more to see the
      differences, to merge them, and so on.

   o  As many existing IDN Tables are practicable SHOULD be able to be
      migrated to the new format with all applicable logic retained.

   It is explicitly NOT the goal of this format to:

   o  Stipulate what code points should be listed in an IDN Table by a
      zone administrator.  What registration policies are used for a
      particular zone is outside the scope of this memo.

   o  Stipulate what a consumer of an IDN Table must do when they
      determine a particular domain is valid or invalid; or arrive at a
      set of computed IDN variants.  IDN Tables are only used to



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      describe rules for computing code points, but does not prescribe
      how registries and other parties utilise them.

















































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3.  IDN Table XML Format

3.1.  Namespace

   The XML Namespace URI is [TBD].

3.2.  Basic structure

   The basic XML framework of the document is as follows:

       <?xml version="1.0"?>
       <idntable xmlns="http://www.iana.org/idn-tables/0.1">
           ...
       </idntable>

   Within the "idntable" element rests two sub-elements.  Firstly is a
   "meta" element that contains all meta-data associated with the IDN
   table, such as its authorship, what it is used for, implementation
   notes and references.  This is followed by a "data" element that
   contains the substantive code-point data.

       <?xml version="1.0"?>
       <idntable xmlns="http://www.iana.org/idn-tables/0.1">
           <meta>
               ...
           </meta>
           <data>
               ...
           </data>
       </idntable>

   A document should contain exactly one "idntable" element, and within
   that optionally one "meta" element and exactly one "data" element.

3.3.  The meta element

   The "meta" element is used to express meta-data associated within the
   IDN table.  It can be used to explain the author or relevant contact
   person, explain what the usage of the IDN table is, provide
   implementation notes as well as references.  The data contained
   within is not required by software consuming the IDN table in order
   to calculate valid IDN labels, or to calculate variants.

3.3.1.  The version element

   The "version" element is used to uniquely identify each version of
   the table being represented.  No specific format is required, but it
   is RECOMMENDED that it be a numerical positive integer, which is



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   incremented with each revision of the file.

   An example of a typical first edition of a document:

       <version>1</version>

   A common alternative is to use a major-minor number scheme, where two
   decimal numbers are used to represent major and minor changes to the
   table.  For example, "1.0" would be the first major release, "1.1"
   would be a minor update to that, and "2.0" would represent a major
   revision.

3.3.2.  The date element

   The "date" element is used to identify the date the table was
   written.  The contents of this element MUST be a valid ISO 8601 date
   string as described in [RFC3339].

   Example of a date:

       <date>2009-11-01</date>

3.3.3.  The language element

   The "language" element signals that the table is associated with a
   specific language or script.  The value of the language element must
   be a valid language tag as described in [RFC5646].  The tag may
   simply refer to a script if the table is not referring to a specific
   language.  There may be multiple language elements for a table if the
   table spans multiple languages and/or scripts.

   Example of an English language table:

      <language>en</language>

   If the table applies to a specific script, rather than a language,
   the "und" language tag should be used followed by the relevant
   [RFC5646] script subtag.  For example, for a Cyrillic script table:

      <language>und-Cyrl</language>

3.3.4.  The domain element

   This optional element refers to a domain to which this policy is
   applied.

       <domain>example</domain>




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   There may be multiple <domain> tags used to reflect a list of
   domains.

3.3.5.  The description element

   The "description" element is a free-form element that contains any
   additional relevant description.  Typically, this field contains
   authorship information, as well as additional context on how the
   table was formulated (such as with references), and how it has been
   applied.

   The element has an optional "type" attribute, which refers to the
   media type of the enclosed data.  If the description lacks a type
   field, it will be assumed to be plain text.

   The description elements describe information relating to the IDN
   table that is useful for the user of the table in its interpretation.
   This may explain the history, the rationale, reference sources etc.
   It may also contain authorship information.

   The "type" attribute may be used to specify the encoding within
   description element.  The attribute should be a valid MIME type.  If
   supplied, it will be assumed the contents is content of that
   encoding.  Typical types would be "text/plain" or "text/html". "text/
   plain" will be assumed if no type attribute is specified.

3.4.  The data element

   The "data" element contains the code point data the comprises the
   registry policy.  It describes registry policy using a series of XML
   elements that either represent individual code points, or ranges of
   code points.

   The data may use the "char" and "range" elements to specify code
   points, and code ranges.

   Discrete permissable code points or code point sequences may be
   stipulated with a "char" element, e.g.

       <char cp="002D"/>

   Ranges of permissable code points may be stipulated with a "range"
   element, e.g.

       <range first-cp="0030" last-cp="0039"/>

   Codepoints must be expressed in hexadecimal, i.e. according to the
   standard Unicode convention without the prefix "U+".  The rationale



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   for not allowing other encoding formats, including native Unicode
   encoding in XML, is explored in [UAX42].  The XML conventions used in
   this format, including the element and attribute names, mirror this
   document where practical and reasonable to do so.

3.4.1.  Sequences

   A sequence of two or more code points may be specified in a table,
   when the exact sequence of code points is required to occur in order
   for the consituent elements to be eligible.  This approach allows
   representation of policy where a specific code point is only eligible
   when preceded or followed by another code point.  For example, in
   order to represent the eligibility of the MIDDLE DOT (U+00B7) only
   when both preceded and followed by the LATIN SMALL LETTER L (U+006C):

   <char cp="006C 00B7 006C"/>

3.4.2.  Variants

   While most tables typically only determine code point eligibility,
   others additionally specify a mapping of code points to other code
   points, known as "variants".  What constitutes a variant is a matter
   of policy, and varies for each implementation.

3.4.2.1.  Basic variants

   Variants are specified as one of more children of a "char" element.

   For example, to map LATIN SMALL LETTER V (U+0076) as a variant of
   LATIN SMALL LETTER U (U+0075):

   <char cp="0075">
     <var cp="0076"/>
   </char>

   A sequence of multiple code points can be specified as a variant of a
   single code point.  For example, the sequence of LATIN SMALL LETTER O
   (U+006F) then LATIN SMALL LETTER E (U+0065) can be specified as a
   variant for an LATIN SMALL LETTER O WITH DIAERESIS (U+00F6) as
   follows:

   <char cp="00F6">
     <var cp="006F 0065"/>
   </char>

   Variants are specified in only on direction.  For symmetric variants,
   the inverse of the variant must be explicitly specified:




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   <char cp="006F 0065">
     <var cp="00F6"/>
   </char>

   It is not possible to specify variants for ranges.

3.4.2.2.  Null variants

   To specify a null variant, which is a variant string that maps to no
   codepoint, use an empty cp attribute.  For example, to mark a string
   with a ZERO WIDTH NON-JOINER (U+200C) to the same string without the
   ZERO WIDTH NON-JOINER:

   <char cp="200C">
     <var cp=""/>
   </char>

3.4.2.3.  Conditional variants

   At its basis, generation of variants are conditional on a specific
   code point or set of code points.  However, in some instances
   registries perform control based on other attributes that can not
   solely be determined based on simple code point comparisons.  For
   example, in some tables utilising the Arabic script, the Arabic
   contextual form is a determinant in which variants are used.  The
   contextual form can not be derived solely from the code point, as the
   code point is the same for the various forms.

   The IDN table provides for conditioning generation variants on
   specific instances as follows, using the "when" attribute.

   arabic-initial  Based on context, the code point would be presented
        in its Arabic Initial form.

   arabic-isolated  Based on context, the code point would be presented
        in its Arabic Isolated form.

   arabic-medial  Based on context, the code point would be presented in
        its Arabic Medial form.

   arabic-final  Based on context, the code point would be presented in
        its Arabic Final form.

   For example, to mark ARABIC LETTER ALEF WITH WAVY HAMZA BELOW
   (U+0673) as a variant of ARABIC LETTER ALEF WITH HAMZA BELOW
   (U+0625), but only when it appears in isolated or final forms:





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   <char cp="0625">
     <var cp="0673" when="arabic-isolated"/>
     <var cp="0673" when="arabic-final"/>
   </char>

3.5.  Example table

   A sample complete XML IDN table is as follows.

       <?xml version="1.0"?>
       <idntable xmlns="http://www.iana.org/idn-tables/0.1">
           <meta>
                <version>1</version>
                <date>2010-01-01</date>
                <language>sv</language>
                <domain>example</domain>
                <description type="text/html">
                <![CDATA[
                    This language table was developed with the
                    <a href="http://swedish.example/">Swedish
                    examples institute</a>.
                ]]>
                </description>
           </meta>
           <data>
               <range first-cp="0061" last-cp="007A"/>
               <char cp="00E4"/>
           </data>
       </idntable>






















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4.  Processing a label against a table

4.1.  Determining eligibility for a label

   In order to use a table to test a specific IDN table for membership
   in the table, a consumer of an IDN table must iterate through each
   code point within a given U-label, and test that each code point is a
   member of the IDN table.  If any code point is not a member of the
   IDN Table, it shall be deemed as not eligible in accordance with the
   table.

   A code point is deemed a member of the table when it is listed with
   the <char> element, and all necessary condition listed in "when"
   attributes are correctly satisfied.

4.2.  Determining variants for a label

   For a given eligible label, the set of variants is deemed to be each
   possible permutation of <var> elements, whereby all "when" attributes
   are correctly satisfied for each code point in the given permutation.































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5.  Conversion between other formats

5.1.  RFC 3743 Language Variant Table

   All attributes can be retained in conversion from an [RFC3743]
   language variant table to this XML format.

   This XML format can be converted to the format described in
   [RFC3743], with the following caveats:

   o  Version numbers not expressed as integers will not satisfy the
      ABNF formatting for [RFC3743].

   o  Much of the additional meta data can not be expressed in the text
      format (although can be supplied as comments in the text file).

   o  The [RFC3743] format only allows for two variant classes, those
      that are preferred and those that are regular.  Other distinctions
      will be lost.

   o  No ability to retain conditional variants.

5.2.  RFC 4290 Model Table Format

   All attributes can be retained in conversion from the [RFC4290] model
   table format to this XML format.

   Tables similarly can be converted to the format described in
   [RFC4290] with the same caveats as the [RFC3743] format, and
   additionally the inability to classify variants into groups such as
   "preferred".




















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6.  IANA Considerations

   This document does not specify any IANA actions.
















































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7.  Security Considerations

   There are no security considerations for this memo.
















































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8.  References

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC3743]  Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint
              Engineering Team (JET) Guidelines for Internationalized
              Domain Names (IDN) Registration and Administration for
              Chinese, Japanese, and Korean", RFC 3743, April 2004.

   [RFC4290]  Klensin, J., "Suggested Practices for Registration of
              Internationalized Domain Names (IDN)", RFC 4290,
              December 2005.

   [RFC5564]  El-Sherbiny, A., Farah, M., Oueichek, I., and A. Al-Zoman,
              "Linguistic Guidelines for the Use of the Arabic Language
              in Internet Domains", RFC 5564, February 2010.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

   [UAX42]    Unicode Consortium, "Unicode Character Database in XML".





























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Appendix A.  RelaxNG Schema


   <?xml version="1.0" encoding="UTF-8"?>
   <grammar ns="http://www.iana.org/idn-tables/0.1"
     xmlns="http://relaxng.org/ns/structure/1.0">
     <define name="language-tag">
       <text/>
     </define>
     <define name="domain-name">
       <text/>
     </define>
     <define name="code-point">
       <text/>
     </define>
     <define name="variant-condition">
       <text/>
     </define>
     <define name="point-single">
       <element name="char">
         <attribute name="cp">
           <ref name="code-point"/>
         </attribute>
         <zeroOrMore>
           <ref name="point-variant"/>
         </zeroOrMore>
       </element>
     </define>
     <define name="point-variant">
       <element name="var">
         <attribute name="cp">
           <ref name="code-point"/>
         </attribute>
         <optional>
           <attribute name="type"/>
         </optional>
         <optional>
           <attribute name="when">
             <ref name="variant-condition"/>
           </attribute>
         </optional>
       </element>
     </define>
     <define name="point-multiple">
       <element name="range">
         <attribute name="first-cp">
           <ref name="code-point"/>
         </attribute>



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         <attribute name="last-cp">
           <ref name="code-point"/>
         </attribute>
         <text/>
       </element>
     </define>
     <define name="points">
       <oneOrMore>
         <choice>
           <ref name="point-single"/>
           <ref name="point-multiple"/>
         </choice>
       </oneOrMore>
     </define>
     <start>
       <ref name="idn-table"/>
     </start>
     <define name="idn-table">
       <element name="idntable">
         <optional>
           <ref name="meta-section"/>
         </optional>
         <ref name="data-section"/>
       </element>
     </define>
     <define name="meta-section">
       <element name="meta">
         <zeroOrMore>
           <choice>
             <optional>
               <element name="version">
                 <text/>
               </element>
             </optional>
             <optional>
               <element name="date">
                 <text/>
               </element>
             </optional>
             <zeroOrMore>
               <element name="language">
                 <ref name="language-tag"/>
               </element>
             </zeroOrMore>
             <zeroOrMore>
               <element name="domain">
                 <ref name="domain-name"/>
               </element>



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             </zeroOrMore>
             <zeroOrMore>
               <element name="description">
                 <attribute name="type"/>
                 <text/>
               </element>
             </zeroOrMore>
           </choice>
         </zeroOrMore>
       </element>
     </define>
     <define name="data-section">
       <element name="data">
         <ref name="points"/>
       </element>
     </define>
   </grammar>


































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Appendix B.  Acknowledgements

   This format builds upon the work on documenting IDN tables by a
   number of other parties, most significantly that of the the Joint
   Engineering Team published as [RFC3743], and [RFC5564] published by
   the Arabic-language community.

   Contributions that have helped shape this document have been
   contributed by Francisco Arias, Mark Davis, Nicholas Ostler, Thomas
   Roessler, Steve Sheng and Andrew Sullivan.









































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Appendix C.  Editorial Notes

   This appendix to be removed prior to final publication.

C.1.  Known Issues and Future Work

   o  An optional mechanism for explicitly nominating the registry
      action associated with a computed variant could be added.  For
      example, an "action" attribute to the <var> element could specify
      one of the following: "allocate", "block", "delegate", "mirror" or
      "withhold".  Each of these actions would need to be formally
      defined.

   o  The tables may benefit from a unique identifier, such as an "id"
      attribute on the <idntables> element.

   o  A method of specifying the origin URI for a table, and an
      expiration or refresh policy, as meta-data may be a useful way to
      declare how the table will be updated.

   o  A more formal step-wise description of how variants are computed,
      including the methodology for assessing contextual rules, needs to
      be supplied.

C.2.  Sample tables and running code

   Some sample tables using this format, as well as a basic
   implementation of this specification, is posted at
   https://github.com/kjd/idntables

C.3.  Change History

   -00  Initial draft.


















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Author's Address

   Kim Davies
   Internet Corporation for Assigned Names and Numbers
   4676 Admiralty Way
   Suite 330
   Marina del Rey, CA  90292
   US

   Phone: +1 310 823 9358
   Email: kim.davies@icann.org
   URI:   http://www.iana.org/







































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