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Versions: 00                                                            
Internet Engineering Task Force                        Leslie L. Daigle
draft-daigle-urnframework-00.txt         Bunyip Information Systems Inc
INTERNET-DRAFT                                         Patrik Faltstrom
                                                          Tele2/Swipnet
                                                        Renato Iannella
                                                           DSTC Pty Ltd

                                                          June 13, 1996.



  A Framework for the Assignment and Resolution of Uniform Resource Names

----------------------------------------
Abstract
----------------------------------------

The main purpose of URNs is to serve as persistent resource identifiers,
where each URN may potentially need to be usable for several decades.
A primary goal of the URN framework is to provide a mechanism whereby a
URN can be resolvable for many decades, while still allowing the
resolution services for that URN to be provided by the parties responsible
for maintenance of the information about that URN.  The Uniform Resource Name
framework abstract description is proposed as a means of handling URN
identifiers in modular layers of information management.  From the standpoint
of the bearer of a URN, this means that much of the underlying support for a
given URN or collection may change without disrupting the identification
capacities of the URN.


----------------------------------------
Status of this draft
----------------------------------------

    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.    Internet-Drafts may  be updated,  replaced,  or
    obsoleted by  other  documents  at  any  time.     It  is  not
    appropriate to use  Internet-Drafts as  reference material  or
    to cite them other  than as a  ``working draft'' or ``work  in
    progress.''

    To learn  the current  status  of any  Internet-Draft,  please
    check the 1id-abstracts.txt listing contained in the Internet-
    Drafts Shadow Directories  on ds.internic.net,  nic.nordu.net,
    ftp.isi.edu, or munnari.oz.au.

    This draft expires November 13, 1996.

    Updated versions and related information can be found at:

        http://www.bunyip.com/research/ietf/urn-bof


----------------------------------------
Introduction
----------------------------------------

The main purpose of URNs is to serve as persistent resource identifiers,
where each URN may potentially need to be usable for several decades.
A primary goal of the URN framework is to provide a mechanism whereby a
URN can be resolvable for many decades, while still allowing the
resolution services for that URN to be provided by the parties responsible
for maintenance of the information about that URN.  Since the resources
named by a URN may change ownership over time, the resolution services
for a URN must be able to change without changes to the URN itself.

The Uniform Resource Naming framework defines the structures and services
required in order to support uniform resource naming across a number of
different namespaces.  The underlying characteristics of these namespaces may
vary considerably, but the URN framework lays out the basic requirements a
namespace must (claim to) live up to in order to be supported as a partition
of the URN namespace. When this work is complete, these requirements will
exist in the form of an objectively verifiable checklist against which new
namespaces can be compared/supporting structures built.

The URN framework aims to provide flexible methods to support various
'resolution services' for URNs.  The resolution service will provide a client
with access to the named resource. The URN framework will provide the client
with the ability to instantiate these resolution services, in a manner that
will not bind any client or service to protocol dependant technologies.

The URN framework abstract description is proposed as a means of handling the
URN identifiers in modular layers of information management.  From the
standpoint of the bearer of a URN, this means that much of the underlying
support for a given URN or collection may change without disrupting the
identification capacities of the URN.  For example, the resolution service(s)
used by a collection may move or change format entirely, without affecting the
validity of the URN.

Beyond accommodating differences in individual namespaces, this framework
is also designed to modularize authority in such a way as to keep information
maintenance close to the responsible entity.  For example, if a resource
location changes, only the final level of resolution needs to be made
aware of the change.


----------------------------------------
Syntax
----------------------------------------

For the purposes of this document, the following informal syntax is used:

        URN:<NID>:<NSS>

NID is the Namespace Identifier and NSS is the Namespace Specific String.  Each
namespace defines the structure of its NSS, and the Namespace ID is used to
determine the _syntactic_ interpretation of the Namespace Specific String to
the extent of extracting the Naming Authority information.  This may be
done by providing rules for extracting specific Naming Authority ID information
from the NSS, or by having a specified set of Naming Authorities for an
entire namespace.  The NID[+NA] serves as a key to finding the location of
resolution services.  The protocol used to resolve the name is independent of
the name itself.  This construct allows the incorporation of different name
structures.

Examples:

        URN:duns:002372413:annual-report-1997

In this example, "duns" is the NID, and "002372413:annual-report-1997" is
the NSS.

        URN:inet:gatech.edu:olympic-schedule-1997

Here, "inet" is the NID, and "gatech.edu:olympic-schedule-1997" is the NSS.


Each of the "duns" and "inet" namespaces define rules for the syntactic
interpretation of the NSS to the extent of extracting an NA string.


----------------------------------------
URN Resolution through Registries
----------------------------------------

The URN framework provides URN resolution infrastructure in the shape
of an abstract description of registries of namespaces and naming authorities.
Resolution of a URN, when possible,  can be accomplished by consulting these
registries, although client software may implement strategies for optimization
of the process.

This default method of resolution-with-registries proceeds as follows:

        . A NID registry consulted get a description of the NSS.  (See
          draft-daniel-naptr-01.txt for a description of the implementation of
          such an NID registry).

        . If there is a NA string in the NSS, the next step of the resolution
          is to look up the NID+NA; otherwise the NID is used again in
          this step of resolution.  The lookup occurs in a resolution
          authority registry (see draft-daniel-naptr-01.txt for a
          description of the implementation of such a registry) to
          identify one or more resolution services for the result.

        . The URN is passed to one of the resolution services.

Note that this document refers to "a global NID registry".  There is
still discussion underway as to the best means of handling public and private
namespaces and different ways of implementing registries.

Pictorially, this can be represented as:


             URN:<NID>:<NSS>
                    |
                    v
          +---------------------+
          | Global NID Registry |
          +---------------------+
                    |
                    |
                 (one of)
          +---------+-----------+
          |                     |
          v                     v
      NID (No NA        NA (extracted from NSS)
       extracted)           + NID
          |                     |
          |                     |
          |        +------------+
          |        |
          |        |
          v        v
    +----------------+
    | Resolution     |
    | Authority      |
    | Registry       |
    +----------------+
           |
           |  (ranked in order of preference)
           +------------------------------------+-----(...)------+
           |                                    |                |
           v                                    v                v
        Resolution                         Resolution         Resolution
        Service1 ID                        Service2  ID       ServiceN ID
           |
           |
           |
           |
           v
    +----------------+
    | BrandX         |
    | URN            |
    | Resolution     |
    | Service        |
    +----------------+
           |
           v
        <result>


N.B.:  <result> is defined abstractly -- it might be the desired resource,
a description of the resource, the location of the resource, etc.

NID registry:

While there needs to be some form of global NID registry (which is not
an uncommon requirement for Internet infrastructure, e.g., the DNS service),
it is possible that a given client will refer first (or exclusively) to a
local NID registry.  This will certainly be useful for closed software
information systems.

It is expected that the NID registry will be fairly small, and pretty
involatile.  It is expected that caching will be quite successful in handling
the majority of requests.

Some namespaces will not want to publish rules for parsing names -- i.e., the
(partial) decoding of the NSS might be considered violation of the proprietary
nature of the name assignment scheme, giving the world at large more
information about the information in the namespace than the namespace's owner
is happy about.  Such namespaces can either opt to pre-pend other indications
of naming authorities in translating their names into NSS's, or these will
fall into the category of URN's from which the NA cannot be extracted.


Resolution Authority Registry:

Once the NA (if any) has been extracted from the URN, the client
consults the Resolution Authority Registry to determine who can
resolve names issued in that namespace by that naming authority.
Depending on the client software, there may be more than one
resolution authority registry that can be consulted.


Examples:

        URN:duns:002372413:annual-report-1997

If the duns namespace does not provide rules for extracting the NA information
from the NSS, NA's for the whole namespace must be provided.

        URN:inet:gatech.edu:olympic-schedule-1997

The inet namespace may provide rules for extracting "gatech.edu" as the
key for composing an NA that should be looked up in the Naming Authority
Registry.

Similarly,

        URN:message-id:199606071447.KAA20718@cs.utk.edu

The message-id namespace may provide rules for extracting "cs.utk.edu" as
the key for compsoin an NA that should be looked up in the Naming Authority
Registry.


----------------------------------------
Clients can do what they want...
----------------------------------------

In providing the above as the default URN resolution procedure,
it is expected that there will be at least one "system" (infrastructure)
deployed to support it -- some global name registry,  and a set of
NA identification servers.  Registration in these services is
required as a step in becoming an official URN-supported namespace.  This
is required in order to be able to ensure global fall-back mechanisms for
resolution of orphaned or migrated resources.

Nevertheless, the resolution strategy used by any client is chosen by the
developers of that client.  For example, a given application may choose to
provide and support a directory of often-used URNs, and its client software
may first consult that directory.  Defining the reliability and optimality
of such strategies is beyond the scope of the URN framework; may the best
strategy win.  The global infrastructure that _is_ provided by the URN
framework  is designed to ensure the overall goals of URNs -- global scope,
persistence, etc.



----------------------------------------
The URN Framework
   -- what is in, what is not
----------------------------------------

This proposed URN framework addresses the URN requirements as laid out in RFC
1737.  Some of these are provided by the infrastructure of the framework itself,
some are defined as characteristics a given namespace must support in order to
be considered eligible to participate in the URN framework, and a few are
considered to lie within the realm of individual namespaces (e.g.,
characteristics that are important to one community, but that impede the
implementation of characteristics necessary to another).

In particular, the URN framework provides global scope, allows persistence,
independence, and legacy support.  Participating Namespaces must claim to
provide global uniqueness in the URNs generated in order to be part of the
URN framework, although they may vary in how they provide persistence and
scalability.


----------------------------------------
Namespace Identifier Requirements and
Administration
----------------------------------------

Some set of criteria must be established to govern what can and cannot
be used as a (top-level) namespace (NID assignment).  This can include:

        . demonstration of an established namespace management system
          (including an overview of mechanisms for preventing the
          duplication/reassignation of name identifiers.  These mechanisms
          are particular to the individual namespaces).
        . multi-organization participation in the naming system
        . rules on how names are assigned, name assignment authority
          delegation
        . provision of escape clause



----------------------------------------
Related issues
----------------------------------------

The URN framework, described here in its abstract form, is meant to provide
the infrastructure for a system that _can_ fulfill the desiderata of URN
systems.  This section describes certain stated issues that are handled
indirectly by the URN framework -- that is, the hooks are available in the
abstract framework, but the implementation will be dependent on elements that
are outside the scope of the URN infrastructure per se.


Lexical Equivalence

This definition of the abstract URN framework does not immediately provide
mechanisms to determine equivalence of two URNs.  That is, in order to
accommodate the variety of existing and proposed namespaces, it is not
possible to define a single scheme that would incorporate this ability.
Nevertheless, there is every likelihood that single resources may be
assigned more than one URN (under different naming schemes, or as the
resources are included in different perspectives of a collection, for
instance).  It is expected that, where needed, individual services for
determining "equivalence" will evolve.


Authority Over Name Strings

The modular nature of the framework distributes authority across different
levels in the resolution process.  Therefore, while the Global NID
Registry will provide the official response about what Resolution Authority
Registries are registered to handle a given URN, it has nothing to say
about the NSS.  Similarly, individual Resolution Services maintain authority
for resolving the URN to a particular result, but they have make no
authoritative statements about a namespace.

Rules for individual namespaces are determined by the owners of the
namespace before they are registered in the NID registry.  Authority
of assignment of individual names within the namespace is also dependent
on the individual namespace, and is not part of the URN resolution framework.



Scope of Grandfathering

Grandfathering of existing namespaces under the URN framework will be handled
in the same way as the creation of new partitions -- a proposal must be
put forward to demonstrate that the namespace can fulfill the requirements
of URN namespace partitions (e.g., generating globally unique URN identifiers)
and what rules will be registered in the Global NID Registry.

----------------------------------------
Acknowledgements
----------------------------------------

The URN work was initiated as part of the IETF URI Working Group.  When
that group was closed at the Stockholm IETF in July, 1995, interested
parties continued to meet to move the work forward.

In addition to the URN BOF held at the Dallas IETF in December, 1995,
three voluntary meetings have been organized (in Knoxville, Montreal,
and Los Alamos).  This document is a direct product of those discussions,
and the following attendees must be thanked for their hard work in helping
move this effort forward:

Ron Daniel
David Ely
Dirk van Gulik
Dan Laliberte
Michael Mealling
Keith Moore
Keith Shafer
Michael Shapiro
Reed Wade
Stuart Weibel
Chris Weider
Ted Wolf



----------------------------------------
Authors' Addresses
----------------------------------------

Leslie L. Daigle
Bunyip Information Systems Inc.
310 Ste. Catherine St. West
Suite 300
Montreal, Quebec, Canada
H2X 2A1
voice: (514) 875-8611
fax: (514) 875-8134
e-mail: leslie@bunyip.com

Patrik Faltstrom
Tele2/Swipnet
Box 62
Borgarfjordsgatan 16
S-164 94 Kista
Sweden
Phone: +46-8-56264000
Fax:   +46-8-56264200
Email: paf@swip.net

Renato Iannella
Research Data Network CRC
DSTC Pty Ltd
Gehrmann Laboratories
University of Queensland
Australia
Phone: +61-7--3365-4310
Fax: +61-7--3365-4311
Email:  renato@dstc.edu.au