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Versions: 00 01 02 03 04 rfc3406                                        
Internet-Draft                                                 L. Daigle
URN WG                                          Thinking Cat Enterprises
Expires May 11, 2001                                        D. van Gulik
Category: Best Current Practice                               WebWeaving
draft-ietf-urn-rfc2611bis-00.txt                             R. Iannella
                                                            DSTC Pty Ltd
                                                            P. Faltstrom
                                                       November 10, 2000

                  URN Namespace Definition Mechanisms

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
     Task Force (IETF), its areas, and its working groups.  Note that
     other groups may also distribute working documents as Internet-

     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

     The list of current Internet-Drafts can be accessed at

     The list of Internet-Draft Shadow Directories can be accessed at


   The URN WG has defined a syntax for Uniform Resource Names (URNs)
   [RFC2141], as well as some proposed mechanisms for their resolution
   and use in Internet applications ([RFCXXXX], [RFCYYYY]).  The whole
   rests on the concept of individual "namespaces" within the URN
   structure.  Apart from  proof-of-concept namespaces, the use of
   existing identifiers in URNs has been discussed ([RFC2288]), and this
   document lays out general definitions of and mechanisms for
   establishing URN "namespaces".

   This document obsoletes RFC2611.

   Discussion of this document should be directed to urn-ietf@ietf.org

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Table of Contents

   Abstract ........................................................  1
   Table of Contents ...............................................  2
   1.0 Introduction ................................................  2
   2.0 What is a URN Namespace? ....................................  3
   3.0 URN Namespace (Registration) Types ..........................  3
   3.1  Experimental Namespaces ....................................  4
   3.2 Informal Namespaces .........................................  4
   3.3 Formal Namespaces ...........................................  4
   4.0 URN Namespace Registration, Update, and NID Assignment
       Process .....................................................  5
   4.1 Experimental ................................................  5
   4.2 Informal ....................................................  6
   4.3 Formal ......................................................  6
   5.0 Illustration ................................................  8
   5.1 Example Template ............................................  8
   5.1 Registration steps in practice .............................. 10
   6.0 Security Considerations ..................................... 11
   7.0 IANA Considerations ......................................... 11
   8.0 References .................................................. 11
   9.0 Authors' Addresses .......................................... 12
   10.0 Appendix -- URN Namespace Definition Template .............. 13

1.0 Introduction

   Uniform Resource Names (URNs) are resource identifiers with the
   specific requirements for enabling location independent
   identification of a resource, as well as longevity of reference.
   There are 2 assumptions that are key to this document:

   Assumption #1:

      Assignment of a URN is a managed process.

      I.e., not all strings that conform to URN syntax are necessarily
      valid URNs.  A URN is assigned according to the rules of a
      particular namespace (in terms of syntax, semantics, and process).

   Assumption #2:

      The space of URN namespaces is managed.

      I.e., not all syntactically correct URN namespaces (per the URN
      syntax definition)  are valid URN namespaces.  A URN namespace
      must have a recognized definition in order to be valid.

   The purpose of this document is to outline a mechanism and provide a
   template for explicit namespace definition, along with the mechanism

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   for associating an identifier (called a "Namespace ID", or NID) which
   is registered with the Internet Assigned Numbers Authority, IANA.

   Note that this document restricts itself to the description of
   processes for the creation of URN namespaces.  If "resolution" of any
   so-created URN identifiers is desired, a separate process of
   registration in a global NID directory, such as that provided by the
   DDDS system [RFCXXXX], is necessary.  See [RFCYYYY] for information
   on obtaining registration in the DDDS global NID directory.

2.0 What is a URN Namespace?

   For the purposes of URNs, a "namespace" is a collection of uniquely-
   assigned identifiers.  A URN namespace itself has an identifier in
   order to

      - ensure global uniqueness of URNs
      - (where desired) provide a cue for the structure of the

   For example, ISBNs and ISSNs are both collections of identifiers used
   in the traditional publishing world; while there may be some number
   (or numbers) that is both a valid ISBN identifier and ISSN
   identifier, using different designators for the two collections
   ensures that no two URNs will be the same for different resources.

   The development of an identifier structure, and thereby a collection
   of identifiers, is a process that is inherently dependent on the
   requirements of the community defining the identifier, how they will
   be assigned, and the uses to which they will be put.  All of these
   issues are specific to the individual community seeking to define a
   namespace (e.g., publishing community, association of booksellers,
   protocol developers, etc); they are beyond the scope of the IETF URN

   This document outlines the processes by which a collection of
   identifiers satisfying certain constraints (uniqueness of assignment,
   etc) can become a bona fide URN namespace by obtaining a NID.  In a
   nutshell, a template for the definition of the namespace is completed
   for deposit with IANA, and a NID is assigned.  The details of the
   process and possibilities for NID strings are outlined below; first,
   a template for the definition is provided.

3.0 URN Namespace (Registration) Types

     There are 3 categories of URN namespaces defined here,

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   distinguished by expected level of service and required procedures
   for registration.  Registration processes for each of these namespace
   types are given in Section 4.0.

3.1  Experimental Namespaces

   These are not explicitly registered with IANA.  They take the form


   No provision is made for avoiding collision of experimental NIDs;
   they are intended for use within internal or limited experimental

3.2 Informal Namespaces

   These are fully fledged URN namespaces, with all the rights and
   requirements associated thereto.  Informal namespaces can be
   registered in global registration services.  They are required to
   uphold the general principles of a well-managed URN namespace --
   providing persistent, unique identification of resources.  Informal
   and formal namespaces (described below) differ in the NID assignment.
   IANA will assign an alphanumeric NID to registered informal
   namespaces, per the process outlined in Section 4.0.

3.3 Formal Namespaces

   A formal namespace may be requested, and IETF review sought, in cases
   where the publication of the NID proposal and the underlying
   namespace will provide benefit to an open and broad base of the
   Internet community.  That is, as in any open standards outcome,
   publication of the NID proposal would allow persons not immediately
   associated with the proposer to create new software, or services, or
   otherwise better carry out their own activities than if the NID
   publication had not been made.  Benefits are expected to be in the
   form of open accessibility, interoperability, etc.

   It is expected that Formal NIDs may be applied to namespaces where
   some aspects are not fully open. For example, a namespace may make
   use of an externally managed (proprietary) registry (as, e.g., ISBN
   does), for assignment of URNs in the namespace, but it may still
   provide broad community benefit if the services associated have
   openly-published access protocols.

   In addition to the basic registration information defined in the
   registration template (in the Appendix), a formal namespace request

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   must be accompanied by documented considerations of the need for a
   new namespace and the community benefit of formally establishing the
   proposed URN namespace.

   Additionally, since the goal of URNs is to provide persistent
   identification, some consideration as to the longevity and
   maintainability of the namespace must be given.  The URN WG discussed
   at length the issue of finding objective measures for predicting (a
   priori) the continued success of a namespace.  No conclusion was
   reached -- much depends on factors that are completely beyond the
   technical scope of the namespace.  However, the collective experience
   of the IETF community does contain a wealth of information on
   technical factors that will prevent longevity of identification.  The
   IESG may elect not to publish a proposed namespace RFC if the IETF
   community consensus is that it contains technical flaws that will
   prevent (or seriously impair the possibility of) persistent

4.0 URN Namespace Registration, Update, and NID Assignment Process

   Different levels of disclosure are expected/defined for namespaces.
   According to the level of open-forum  discussion surrounding the
   disclosure, a URN namespace may be assigned or may request a
   particular identifier.  The  "IANA Considerations" document [RFC2434]
   suggests the need to specify update mechanisms for registrations --
   who is given the authority to do so, from time to time, and what are
   the processes.  Since URNs are meant to be persistently useful, few
   (if any) changes should be made to the structural interpretation of
   URN strings (e.g., adding or removing rules for lexical equivalence
   that might affect the interpretation of URN IDs already assigned).
   However, it may be important to introduce clarifications, expand the
   list of authorized URN assigners, etc, over the natural course of a
   namespace's lifetime.  Specific processes are outlined below.

   URN namespace registrations will be posted in the anonymous FTP
   directory "ftp://ftp.isi.edu/in-notes/iana/assignments/URN-

   The registration and maintenance procedures vary slightly from one
   namespace type (as defined in Section 3.0) to another.

4.1 Experimental

   These are not explicitly registered with IANA.  They take the form

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   No provision is made for avoiding collision of experimental NIDs;
   they are intended for use within internal or limited experimental

   As there is no registration, no registration maintenance procedures
   are needed.

4.2 Informal

   These are registered with IANA and are assigned a number sequence as
   an identifier, in the format:

                              "urn-" <number>

   where <number> is chosen by the IANA on a First Come First Served
   basis (see [RFC2434]).

   Registrants should send a copy of the registration template (see the
   Appendix), duly completed, to the


   mailing and allow for a 2 week discussion period for clarifying the
   expression of the registration information and suggestions for
   improvements to the namespace proposal.

   After suggestions for clarification of the registration information
   have been incorporated, the template may be submitted to:


   for assignment of a NID.

   The only restrictions on <number> are that it consist strictly of
   digits and that it not cause the NID to exceed length limitations
   outlined in the URN syntax ([RFC2141]).

   Registrations may be updated by the original registrant, or an entity
   designated by the registrant, by updating the registration template,
   submitting it to the discussion list for a further 2 week discussion
   period, and finally resubmitting it to IANA, as described above.

4.3 Formal

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   Formal NIDs are assigned via IETF Consensus, as defined in [RFC2434]:

     "IETF Consensus - New values are assigned through the IETF
      consensus process. Specifically, new assignments are made via
      RFCs approved by the IESG. Typically, the IESG will seek
      input on prospective assignments from appropriate persons
      (e.g., a relevant Working Group if one exists)."

   Thus, the Formal NID application is made via publication of an RFC
   through standard IETF processes.  The RFC need not be standards-
   track, but it will be subject to IESG review and acceptance pursuant
   to the guidelines written here (as well as standard RFC publication
   guidelines).  The template defined in the Appendix may be included as
   part of an RFC defining some other aspect of the namespace, or it may
   be put forward as an RFC in its own right.  The proposed template
   should be sent to the


   mailing list to allow for a 2 week discussion period  for clarifying
   the expression of the registration information, before the IESG
   reviews the document.

   The RFC must include a "Namespace Considerations" section, which
   outlines the perceived need for a new namespace (i.e., where existing
   namespaces fall short of the proposer's requirements).
   Considerations might include:

        - URN assignment procedures      - URN resolution/delegation
        - type of resources to be identified      - type of services to
   be supported

   NOTE:  It is expected that more than one namespace may serve the same
   "functional" purpose; the intent of the "Namespace Considerations"
   section is to provide a record of the proposer's "due diligence" in
   exploring existing possibilities, for the IESG's consideration.

   The RFC must also include a "Community Considerations" section, which
   indicates the dimensions upon which the proposer expects the Internet
   community to be able to benefit by publication of this namespace.
   Potential considerations include:

        - open assignment and use of identifiers within the namespace
        - open operation of resolution servers for the namespace
   (server)      - creation of software that can meaningfully resolve
   and        access services for the namespace (client)

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   A particular NID string is requested, and is assigned by IETF
   consensus (as defined in [RFC2434]), with the additional constraints
   that the NID string must

        - not be an already-registered NID      - not start with "x-"
   (see Type I above)      - not start with "urn-" (see Type II above)
        - not start with "XY-", where XY is any combination of 2
   ASCII letters  (see NOTE, below)      - be more than 2 letters long

   NOTE: ALL two-letter combinations, and two-letter combinations
   followed by "-" and any sequence of valid NID characters,  are
   reserved for potential use as countrycode- based  NIDs for eventual
   national registrations of URN namespaces.   The definition and
   scoping of rules for allocation of responsibility for such namespaces
   is beyond the scope of this document.

   Registrations may be revised by updating the RFC through standard
   IETF RFC update mechanisms.  Thus, proposals for updates may be made
   by the original authors, other IETF participants, or the IESG.  In
   any case, the proposed updated template must be circulated on the
   urn-nid discussion list, allowing for a 2 week review period.

5.0 Illustration

5.1 Example Template

   The following example is provided for the purposes of illustration of
   the URN NID template described in the Appendix.  Although it is based
   on a hypothetical "generic Internet namespace" that has been
   discussed informally within the URN WG, there are still technical and
   infrastructural issues that would have to be resolved before such a
   namespace could be properly and completely described.

   Namespace ID:
      To be assigned

   Registration Information:

      Version 1
      Date: <when submitted>

   Declared registrant of the namespace:

      Required: Name and e-mail address.
      Recommended:  Affiliation, address, etc.

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   Declared registrant of the namespace:

      Name:           T. Cat
      E-mail:         leslie@thinkingcat.com
      Affiliation:    Thinking Cat Enterprises
      Address:        1 ThinkingCat Way
                      Trupville, NewCountry

   Declaration of structure:

      The identifier structure is as follows:

      URN:<assigned number>:<FQDN>:<assigned US-ASCII string>

      where FQDN is a fully-qualified domain name, and the assigned
      string is conformant to URN syntax requirements.

   Relevant ancillary documentation:

      Definition of domain names, found in:

      RFC1035, November 1987.

   Identifier uniqueness considerations:

      Uniqueness is guaranteed as long as the assigned string is never
      reassigned for a given FQDN, and that the FQDN is never

      N.B.:  operationally, there is nothing that prevents a domain name
      from being reassigned;  indeed, it is not an uncommon occurrence.
      This is one of the reasons that this example makes a poor URN
      namespace in practice, and is therefore not seriously being
      proposed as it stands.

   Identifier persistence considerations:

      Persistence of identifiers is dependent upon suitable delegation
      of resolution at the level of "FQDN"s, and persistence of FQDN

      Same note as above.

   Process of identifier assignment:

      Assignment of these URNs delegated to individual domain name
      holders (for FQDNs).  The holder of the FQDN registration is

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      required to maintain an entry (or delegate it) in the DDDS.
      Within each of these delegated name partitions, the string may be
      assigned per local requirements.

      e.g.  urn:<assigned number>:thinkingcat.com:001203

   Process for identifier resolution:

      Domain name holders are responsible for operating or delegating
      resolution servers for the FQDN in which they have assigned URNs.

   Rules for Lexical Equivalence:

      FQDNs are case-insensitive.  Thus, the portion of the URN

              urn:<assigned number>:<FQDN>:

      is case-insenstive for matches.  The remainder of the identifier
      must be considered case-sensitve.

   Conformance with URN Syntax:

      No special considerations.

   Validation mechanism:

      None specified.



5.1 Registration steps in practice

   The key steps for registration of informal or formal namespaces
   typically play out as follows:

   Informal NID:

     1.  Complete the registration template.  This may be done as part
     of an Internet-Draft.

     2.  Communicate the registration template to urn-nid@apps.ietf.org
     for technical review -- as a published I-D, or text e-mail message
     containing the template.

     3. Update the registration template as necessary from comments, and

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     repeat steps 2 and 3 as necessary.

     4. Once comments have been addressed (and the review period has
     expired) end a request to IANA with the revised registration

   Formal NID:

     1. Write an Internet-Draft describing the namespace and including
     the registration template, duly completed.

     2. Send the Internet-Draft to the I-D editor, and send a copy to
     urn-nid@apps.ietf.org for technical review.

     3. Update the Internet-Draft as necessary from comments, and repeat
     steps 2 and 3 as needed.

     4.  Send a request to the IESG to publish the I-D as an RFC.  The
     IESG may request further changes (published as I-D revisions)
     and/or direct discussion to designated working groups, area
     experts, etc.

     5.  If the IESG approves the document for publication as an RFC,
     send a request to IANA to register the requested NID.

6.0 Security Considerations

   This document largely focuses on providing mechanisms for the
   declaration of public information.  Nominally, these declarations
   should be of relatively low security profile, however there is always
   the danger of "spoofing" and providing mis-information.  Information
   in these declarations should be taken as advisory.

7.0 IANA Considerations

   This document outlines the processes for registering URN namespaces,
   and has implications for the IANA in terms of registries to be
   maintained.  In all cases, the IANA should assign the appropriate NID
   (informal or formal), as described above, once an IESG-designated
   expert has confirmed that the requisite registration process steps
   have been completed.

8.0 References

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   [ISO8601]   ISO 8601 : 1988 (E), "Data elements and interchange
               formats - Information interchange - Representation of
               dates and times"

   [RFC2288]   Lynch, C., Preston, C. and R. Daniel, "Using Existing
               Bibliographic Identifiers as Uniform Resource Names", RFC
               2288, February 1998.

   [RFCXXXX]   Mealling, M., "URI Resolution using the Dynamic
                  Delegation Discovery System", RFCXXXX.

   [RFCYYYY]   Mealling, M., "Assignment Procedures for URI Resolution
                 Using DNS", RFCYYYY.

   [RFC2141]   Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC2434]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 2434,
               October 1998.

   [RFC1737]   Sollins, K. and L. Masinter, "Functional Requirements for
               Uniform Resource Names", RFC 1737, December 1994.

   [RFC2276]   Sollins, K., "Architectural Principles of Uniform
               Resource Name Resolution", RFC 2276, January 1998.

9.0 Authors' Addresses

   Leslie L. Daigle
   Thinking Cat Enterprises

   EMail:  leslie@thinkingcat.com

   Dirk-Willem van Gulik
   Plein 1813 - 5a
   8545 HX Arnhem
   The Netherlands

   Phone:  +39 0332 78 0014 (Phone and Fax)
   EMail:  Dirkx@webweaving.org

   Renato Iannella
   DSTC Pty Ltd
   Gehrmann Labs, The Uni of Queensland

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   AUSTRALIA, 4072

   Phone:  +61 7 3365 4310
   Fax:    +61 7 3365 4311
   EMail:  renato@dstc.edu.au

   Patrik Faltstrom
   Cisco Systems Inc
   170 W Tasman Drive SJ-13/2
   San Jose CA 95134

   EMail: paf@cisco.com
   URL:   http://www.cisco.com

10.0 Appendix -- URN Namespace Definition Template

   Definition of a URN namespace is accomplished by completing the
   following information template.  Apart from providing a mechanism for
   disclosing structure of the URN namespace, this information is
   designed to be useful for

      - entities seeking to have a URN assigned in a namespace (if
      - entities seeking to provide URN resolvers for a namespace (if

   This is particularly important for communities evaluating the
   possibility of using a portion of an existing URN namespace rather
   than creating their own.

   Information in the template is as follows:

   Namespace ID:
      Assigned by IANA.  In some contexts, a particular one may be
      requested (see below).

   Registration Information:

      This is information to identify the particular version of
      registration information:

      - registration version number: starting with 1, incrementing by 1
        with each new version
      - registration date: date submitted to the IANA, using the format

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        as outlined in [ISO8601].

   Declared registrant of the namespace:

      Required: Name and e-mail address.
      Recommended:  Affiliation, address, etc.

   Declaration of syntactic structure:

      This section should outline any structural features of identifiers
      in this namespace.  At the very least, this description may be
      used to introduce terminology used in other sections.  This
      structure may also be used for determining realistic
      caching/shortcuts approaches; suitable caveats should be provided.
      If there are any specific character encoding rules (e.g., which
      character should always be used for single-quotes), these should
      be listed here.

      Answers might include, but are not limited to:

      - the structure is opaque (no exposition) - a regular expression
        for parsing the identifier into components, including naming

   Relevant ancillary documentation:

      This section should list any RFCs, standards, or other published
      documentation that defines or explains all or part of the
      namespace structure.

      Answers might include, but are not limited to:

      - RFCs outlining syntax of the namespace
      - Other of the defining community's (e.g., ISO) documents
        outlining syntax of the identifiers in the namespace
      - Explanatory material introducing the namespace

   Identifier uniqueness considerations: This section should address the
   requirement that URN identifiers be assigned uniquely -- they are
   assigned to at most one resource, and are not reassigned.

   (Note that the definition of "resource" is fairly broad; for example,
   information on "Today's Weather" might be considered a single
   resource, although the content is dynamic.)

   Possible answers include, but are not limited to:

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      - exposition of the structure of the identifiers, and partitioning
        of the space of identifiers amongst assignment authorities which
        are individually responsible for respecting uniqueness rules
      - identifiers are assigned sequentially
      - information is withheld; the namespace is opaque

   Identifier persistence considerations:

      Although non-reassignment of URN identifiers ensures that a URN
      will persist in identifying a particular resource even after the
      "lifetime of the resource", some consideration should be given to
      the persistence of the usability of the URN.  This is particularly
      important in the case of URN namespaces providing global

      Possible answers include, but are not limited to:

      - quality of service considerations

   Process of identifier assignment:

      This section should detail the mechanisms and/or authorities for
      assigning URNs to resources.  It should make clear whether
      assignment is completely open, or if limited, how to become an
      assigner of identifiers, and/or get one assigned by existing
      assignment authorities.  Answers could include, but are not
      limited to:

      - assignment is completely open, following a particular algorithm
      - assignment is delegated to authorities recognized by a
        particular organization (e.g., the Digital Object Identifier
        Foundation controls the DOI assignment space and its delegation)
      - assignment is completely closed (e.g., for a private

   Process for identifier resolution:

      If a namespace is intended to be accessible for global resolution,
      it must be registerd in an RDS (Resolution Discovery System, see
      [RFC2276]) such as DDDS.  Resolution then proceeds according to
      standard URI resolution processes, and the mechanisms of the RDS.
      What this section should outline is the requirements for becoming
      a recognized resolver of URNs in this namespace (and being so-
      listed in the RDS registry).

      Answers may include, but are not limited to:

      - the namespace is not listed with an RDS; this is not relevant

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      - resolution mirroring is completely open, with a mechanism for
        updating an appropriate RDS
      - resolution is controlled by entities to which assignment has
        been delegated

   Rules for Lexical Equivalence:

      If there are particular algorithms for determining equivalence
      between two identifiers in the underlying namespace (hence, in the
      URN string itself), rules can be provided here.

      Some examples include:

      - equivalence between hyphenated and non-hyphenated groupings in
        the identifier string
      - equivalence between single-quotes and double-quotes
      - Namespace-defined equivalences between specific characters, such
        as "character X with or without diacritic marks".

      Note that these are not normative statements for any kind of best
      practice for handling equivalences between characters; they are
      statements limited to reflecting the namespace's own rules.

   Conformance with URN Syntax:

      This section should outline any special considerations required
      for conforming with the URN syntax.  This is particularly
      applicable in the case of legacy naming systems that are used in
      the context of URNs.

      For example, if a namespace is used in contexts other than URNs,
      it may make use of characters that are reserved in the URN syntax.
      This section should flag any such characters, and outline
      necessary mappings to conform to URN syntax.  Normally, this will
      be handled by hex encoding the symbol.

      For example, see the section on SICIs in [RFC2288].

   Validation mechanism:

      Apart from attempting resolution of a URN, a URN namespace may
      provide mechanism for "validating" a URN -- i.e., determining
      whether a given string is currently a validly-assigned URN.  For
      example, even if an ISBN URN namespace is created, it is not clear
      that all ISBNs will translate directly into "assigned URNs".

      A validation mechanims might be:

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      - a syntax grammar
      - an on-line service
      - an off-line service


      This section should outline the scope of the use of the
      identifiers in this namespace.  Apart from considerations of
      private vs. public namespaces, this section is critical in
      evaluating the applicability of a requested NID.  For example, a
      namespace claiming to deal in "social security numbers" should
      have a global scope and address all social security number
      structures (unlikely).  On the other hand, at a national level, it
      is reasonable to propose a URN namespace for "this nation's social
      security numbers".

Daigle                                                         [Page 17]