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Versions: 00 01 02 03 05 06 07 08 rfc2611                               
Internet Draft                               Leslie L. Daigle
August 4, 1998                               Bunyip Information Systems
draft-ietf-urn-nid-req-05.txt                Dirk-Willem van Gulik
                                             ISIS/CEO, JRC Ispra
                                             Renato Iannella
                                             DSTC Pty Ltd
                                             Patrik Faltstrom

      URN Namespace Definition Mechanisms

Status of this Document

     This document is an Internet-Draft.  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-Drafts.

     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."

     To view the entire list of current Internet-Drafts, please check
     the "1id-abstracts.txt" listing contained in the Internet-Drafts
     Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net
     (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East
     Coast), or ftp.isi.edu (US West Coast).

0.0 Abstract

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 ([RFC2168, RFC2169]).
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'.

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
for associating an identifier (called a "Namespace ID", or NID) which
is registered with the Internet Assigned Number 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
NAPTR system [RFC2168], is necessary.  See [NAPTR-REG] for information
on obtaining registration in the NAPTR 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 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 needs
of the identifiers, 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 work.

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 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 applicable)
        . entities seeking to provide URN resolvers for a namespace
          (if applicable)

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).

Declared registrant of the namespace:

        Name and e-mail address.

Declaration of 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.

        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 authorities

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 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.

        Possible answers include, but are not limited to:

        . exposition of the structure of the identifiers, and
          partitioning of the space of identifiers amongst
          assignment authorities
        . 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 resolution.

        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
        . 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 NAPTR.  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

        Answers may include, but are not limited to:

        . the namespace is not listed with an RDS; this is not
        . 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 URN strings in this namespace,
        rules can be provided here.

        Some examples include:

        . mappings between different character set encodings
        . equivalence between hyphenated and non-hyphenated
          groupings in the identifier string

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 have a more generous character set than is
        immediately available with URNs.  This section should flag this
        issue and outline necessary mappings to conform to
        URN syntax.  (E.g., 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:

        . 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
        posit a URN namespace for "this nation's social security

4.0 URN Namespace Registration 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.

There are 3 categories of URN namespaces defined here, distinguished
by expected level of service and required procedures for registration.

          I. Experimental: 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 contexts.

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

                        "iana-" <number>

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

                Registrants should send a copy of the registration
                template (see section 3.0), 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 ([RFC2168]).

        III. Formal:  These are processed through an RFC review
                process.  The RFC need not be standards-track.  The template
                defined in section 3.0 may be
                included as part of the RFC, or a separate message
                referencing the RFC.  The proposed template should
                be sent to the


                mailing list to allow for a 2 week discussion period.

                The registration template should then be sent to


                A particular NID string is requested, and is assigned by IETF
                consensus (as defined in [IANA-CONSIDERATIONS]), with
                the additional constraints that the NID string must
                not start with "x-" (see Type I above) or "iana-" (see Type II
                above), and is not already a registered NID.

                The two-letter country codes are reserved
                for availability for national registrations.

URN namespace registrations will be posted in the anonymous FTP directory

5.0 Example

The following example is provided for the purposes of illustration of
the URN NID template described in section 3.0.  Although it is based on
a posited "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

Declared registrant of the namespace:

        T. Cat

Declaration of structure:

        The identifier structure is as follows:

        URN:<assigned number>:<FQDN>:<assigned 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 reassigned.

        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 assignment.

        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 required to maintain an entry (or delegate it) in the
        NAPTR RDS.  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.



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 References

[IANA-CONSIDERATIONS] H. Alvestrand and T. Narten, "Guidelines for
    Writing an IANA Considerations Section in RFCs",

[RFC2168] Ron Daniel & Michael Mealling, "Resolution of Uniform
    Resource Identifiers using the Domain Name System", RFC 2168,
    June 1997.

[RFC2169] Ron Daniel, "A Trivial Convention for using HTTP in URN
    Resolution", RFC 2169, June 1997.

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

[NAPTR-REG] M. Mealling, "Assignment Procedures for the URI Resolution
    using DNS (RFC2168)", draft-ietf-urn-net-procedures-00.txt.

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

[RFC1737] Karen R Sollins & Larry Masinter, "Functional Requirements
    for Uniform Resource Names", RFC1737, December 1994

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

8.0 Authors' Addresses

Leslie L. Daigle
Bunyip Information Systems Inc
310 Ste. Catherine St. W
Suite 300
Montreal, Quebec, CANADA
H2X 2A1
voice: +1 514 875-8611
fax:   +1 514 875-8134
email:  leslie@bunyip.com

Dirk-Willem van Gulik
Joint Research Centre Ispra
21020 Ispra (Va)
voice: +39 332 78 9549 or 5044
fax:   +39 332 78 9185
email:  Dirk.vanGulik@jrc.it

Renato Iannella
DSTC Pty Ltd
Gehrmann Labs, The Uni of Queensland
voice:  +61 7 3365 4310
fax:    +61 7 3365 4311
email:  renato@dstc.edu.au

Patrik Faltstrom
Borgarfjordsgatan 16
P.O. Box 62
S-164 94 Kista
voice:  +46-5626 4000
fax:    +46-5626 4200
email:  paf@swip.net