# Internet Draft on URNs

Chris Weider (clw@merit.edu)
Fri, 14 May 93 18:03:11 -0400

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    Date: Fri, 14 May 93 18:03:11 -0400

    From: "Chris Weider" <clw@merit.edu>

    Message-Id: <9305142203.AA23447@merit.edu>

    To: uri@bunyip.com

    Subject: Internet Draft on URNs

Gang:
This is the URN draft that Peter and I put together (but unfortunately
did not get distributed) before the Columbus IETF. At that IETF, it was
decided that since our proposal looked so much like the URN we all decided
on that we would make minor mods to our paper and submit it. So here it is!
As always, comments are greatly appreciated. Please note that we have
gotten 'round the recent 'whitespace' controversy by disallowing it in the
URN.... any white space in a presented URN can safely be ignored :^).
Chris Weider

INTERNET--DRAFT Chris Weider
IETF URI Working Group Merit Network, Inc.
Peter Deutsch
Bunyip Information
Systems, Inc.
May, 1993

Uniform Resource Names

Status of this Memo

In this paper, the authors propose an identifier, call the Uniform Resource
Name (URN), which is designed to provide persistent naming for resources
and objects on the Internet.

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."

Please check the I-D abstract listing contained in each Internet
Draft directory to learn the current status of this or any
other Internet Draft.

This Internet Draft expires November 10, 1993.

1: Introduction

A Uniform Resource Name (URN) is an identifier which can be used to uniquely
identify a resource, and is designed to provide persistent naming for
networked objects. This name would stay the same no matter what the
current location(s) of the object was.

2: Motivation

This work comes out of the discussions held at the Uniform Resource Identifier
meetings at the IETF, and from further discussions among interested parties.
Currently, the only standard identification scheme for resources on the Net is
the Uniform Resource Locator (URL) [Berners-Lee 1993]. This "Locator"
is designed to provide a uniform way of specifying location and retrieval
information for networked objects. The URL, however, will not provide a stable,
long-lived reference to a resource as the resources have a bad habit of moving
out from under the locator. Also, a given resource may have multiple URLs if
it resides at a number of different locations on the net, or is available
under a number of different access methods. Thus it is difficult to tell,
given two different URLs, whether the resources they point to are the same
or different without retrieving both of them. The Uniform Resource Name, or
URN, has been designed to alleviate these problems.

3: The Uniform Resource Name (URN)

3.1 Functionality

The URN is designed to provide persistent naming for objects on the net. It
is intended to be used in conjunction with a directory service, which can
provide a URN -> URL mapping [Weider 1993]. This URN-URL architecture allows
permanent references to be made to resources without worrying about their
current locations. It is also intended to provide some detection of duplicates
in responses to queries of various resource location services.
INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

3.2 What URNs are *not*

URNs are not intended to be human-readable in the sense that a human could
look at the URN and determine anything about the contents of the resource.
While the Naming Authority (q.v.) has the final determination of the contents
(subject to the syntax constraints), the Naming Authority is STRONGLY
discouraged from placing metainformation about the resource into the resource's
URN, as the URNs are not expected to be read, and because this paper will
specify only four consistent components of the URN. Although there have been a
number of proposals placing extensive semantics on the contents of the URN
[Spero 1992, Kunze 1993], it was decided by the authors of all the proposals
that all metainformation should be conveyed using another mechanism, and that
the Naming Authority should assume that humans will never look at the contents
of the URN to determine qualities of the resource they are retrieving, and
would not be required to guess from a given URN the URN of a document which
might be related.

3.3 Components of the URN

There are three components to the URN; a wrapper, a Naming Authority identifier,
and an opaque 'name'. The general syntax is:

URN:Naming_Authority_identifier::opaque_string:::

^ | ^ | ^
|_________________ wrapper ___|_______________|

Blanks, <crlf>s, and non-printing characters are NOT allowed. For a full
allowable character set, see section 5.

3.3.1 The wrapper

The wrapper consists of the 4 character header 'URN:', two consecutive
colons to separate the Naming_Authority_Identifier component from the
opaque_string component, and the 3 character trailer ':::'.

3.3.2 The Naming Authority Identifier

The Naming Authority identifier consists of two sub-components, a 'scheme
identifier' and an 'individual identifier'. A scheme identifier is the
name of a protocol or organization which can guarantee the uniqueness and
resolvability of the individual identifier. The individual identifier is
the identifier of an organization which has assigned the opaque string
component to the resource and can resolve the URN to a set of URLs for the
resource. The scheme identifier and the individual identifier are separated by
a colon. For example, typical Naming Authorities might be

IANA:42117

or

ISBN_Publisher_ID:0_201_12
etc.

3.3.3 The Opaque String

The opaque string component of the URN is any string the Naming Authority
wishes to assign to a given resource, subject only to the syntax description

INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

below. As mentioned above, the Naming Authority should not assume that a
human will ever read the URN. Also, the Naming Authority, in assigning an
opaque string to a given resource, should keep the following guidelines in
mind:

1: A given opaque string should be case-insensitive (for compatibility
with very old systems).

2: A given opaque string, once assigned, should never be reused. These
are expected to be persistent names for resources (think in terms
of decades).

3: In assigning an opaque string, and thus creating a URN, the Naming
Authority should make provisions for a URN -> URL mapping
function. This need be nothing more than finding an organization
which is already providing this service for other URNs and making
arrangements to have them translate for the new URN, or could
be as involved as creating a new software agent to provide this
service. Remember that a name is no good without some way of
getting a location.

4: URNs will be returned as pointers from a resource location service.
(See [Weider 1993]). Consequently, a Naming Authority should give
some thought to the assignation of new URNs for resources which
are derived in some fashion from other resources to which that
Authority has already assigned URNs. For example, should the
Postscript version and the ASCII version of a paper have the
same URN? While there are no universally applicable answers to
questions like these (for example, should the Russian and English
versions of a scientific paper have the same URN?) an Authority
should keep in mind that users will want to weed out duplicate
resources in the lists of URNs returned by a resource location
service, and consequently will be doing a lot of equality testing
on the URNs.

4: Setting up as a Naming Authority

There are 2 scheme identifiers listed here; others will no doubt be suggested
and added as this draft circulates. They are:

IANA
ISBN_Publisher_ID

To set one's organization up as a Naming Authority, one can use the ISBN
publisher ID one has been assigned, or one can apply for an Enterprise
Number from the IANA (Internet Assigned Number Authority) if the organization
does not already have one. The general syntax is listed in section 5.

5: Syntax

Below is a BNF like description of the syntax of the URN. Spaces have
been used here to separate components for readability, spaces are NOT ALLOWED
in a syntactically correct URN. Square brackets '[' and ']' are used to
indicate optional parts; a vertical line "|" indicates alternatives.
Single letters and digits stand for themselves. All words of more than one
letter are either expanded further in the syntax or represent themselves.

INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

urn URN: Authority_Id :: opaque_string :::
Authority_Id Scheme_ID [ : Individual ]
Scheme_ID IANA | ISBN_Publisher_ID
Individual xalphas
opaque_string xalphas
xalphas xalpha [ xalphas ]
xalpha a | b | c | d | e | f | g | h | i | j | k | l |
m | n | o | p | q | r | s | t | u | v | w | x |
y | z | A | B | C | D | E | F | G | H | I | J |
K | L | M | N | O | P | Q | R | S | T | U | V |
W | X | Y | Z | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
9 | 0 | - | _ | . | @

6: References

[Kunze 1993] Kunze, John, Resource Citations for Electronic Discovery and
Retrieval, March, 1993. Circulated to ietf-uri mailing list.

[Spero 1992] Spero, Simon, Uniform Resource Numbers, November 1992.
Circulated to ietf-uri mailing list.

[Weider 1993] Weider, Chris and Deutsch, Peter. A Vision of an Integrated
Internet Information Service, March, 1993. Available as

ftp://nic.merit.edu/documents/internet-drafts/draft-ietf-iiir-vision-00.txt

7: Author's addresses

Chris Weider
clw@merit.edu
Merit Network, Inc.
2901 Hubbard, Pod G
Ann Arbor, MI 48109
Phone: (313) 747-2730
Fax: (313) 747-3185

Peter Deutsch
peterd@bunyip.com
Bunyip Information Systems
310 St-Catherine St West
suite 202,
Montreal, Quebec H2X 2A1
CANADA

- Next message: Mark Constable: "Re: message/external-body & URL"
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- Maybe reply: Dave Brennan: "Re: Internet Draft on URNs"
- Reply: John Curran: "Re: Internet Draft on URNs"
- Maybe reply: Terry Winograd: "Re: Internet Draft on URNs"
- Maybe reply: Ed Krol: "Re: Internet Draft on URNs"
- Maybe reply: Ed Krol: "Re: Internet Draft on URNs"
- Reply: Marc Andreessen: "Internet Draft on URNs"
- Maybe reply: Karl Auerbach, Empirical Tools and Technologies, 408/427-5280: "Re: Internet Draft on URNs"
- Maybe reply: Terry Winograd: "Re: Internet Draft on URNs"
- Maybe reply: Dave Brennan: "Re: Internet Draft on URNs"