# Revision of Chris & Peter's URN paper

Chris Weider (clw@merit.edu)
Tue, 19 Oct 93 12:04:46 -0400

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    Date: Tue, 19 Oct 93 12:04:46 -0400

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

    Message-Id: <9310191604.AA06476@merit.edu>

    To: uri@bunyip.com

    Subject: Revision of Chris & Peter's URN paper

Gang:
Here is a revision of the URN draft that we submitted earlier this year. It
has a number of changes from the earlier draft. In addition, Peter has seen
this revision but has not yet had an opportunity to comment; Alan suggested
that I send it out anyway in time for Houston.

Changes from earlier draft:

1) The multiple colon syntax has been removed; individual fields are now
separated by colons, with positional semantics indicating the individual
fields and a 'colon-counting' parse technique.

2) The characters < and > are use as delimiters for the URN. Unlike the
URL, this is built into the syntax of the URN; I still feel there is a need
for termination characters especially when these are going to be cut and
pasted.

3) (Major change) A fifth field has been added, specifying the encoding
scheme used for the opaque string. It seems to me that it would be unwise to
limit the potential character sets usable for the opaque string, particularly
if we're planning for the future. However, we still have those pesky mailers
to deal with... so I have defined one encoding scheme, ASCII encoded ASCII.
While this may seem rather redundant, think about other possibilities such
as ASCII encoded UNICODE, ASCII encoded binary checksums, etc.

Points emphasized more in the current draft:

1) The fact that the naming authority identifier may be hierarchical in
nature, and multi-leveled. Apparently this was not brought out enough in the
previous draft as we kept getting questions about it.

2) The fact that the primary function of the URN is to provide a persistant
(location independent) identifier.

Controversial points still in the draft:

1) The fact that the naming authorities have complete control over the opaque
string assignment, BUT that they are encouraged not to have semantically
meaningful subparts in the opaque string, which would give the human reader
an indication of its use. I sent out a message about the dangers of placing
comparative attributes (such as version number) in the URN itself; since I
didn't get any response, I must assume that everyone agrees with me
(wry grin)...

Well, with that, here's the latest draft.
Chris

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

Uniform Resource Names

Status of this Memo

In this paper, the authors propose an identifier, called 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 March 20, 1994.

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.

INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

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.

3.2 What URNs are *not*

URNs are not required 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 five 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 five components to the URN, separated by colons; the keyword
'URN', a code specifying the character set encoding of the rest of the URN, a
naming authority scheme identifier, a naming authority identifier, and an
opaque string. The URN is surrounded by the characters '<' and '>', which are
part of the syntax. Each part is described below. No component of the URN
can contain the characters ':', '>', ' ', or '\' unless they are escaped by a
backslash character '\'.

3.3.1 URN examples

<URN:ASCII:IANA:merit.edu:1929642>

<URN::ISBN_Publisher_ID:0_201_12:xyzx\:mnopq>

<URN:ASCII:IANA:12456:1\:<\>\:2345>

3.3.2 The character set encoding code

This string identifies the encoding scheme used for the rest of the URN.
There is only one defined at this time, ASCII, which indicates that the
rest of the URN is ASCII encoded ASCII. If this component is empty,
the default encoding scheme is assumed. The default encoding scheme is
ASCII.

INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

3.3.3 The naming authority scheme identifier

The naming authority scheme identifier is a string which is the name of a
protocol or organization which guarantees the uniqueness of the naming
authority identifier which follows. Naming authority scheme identifiers defined
at this time are

IANA
ISBN_Publisher_ID

3.3.4 The naming authority identifier

This string, along with the naming authority scheme identifier, identifies a
naming authority that may assign URNs to resources. This string may have
internal syntax depending on the naming authority scheme identifier associated
with it; for example, the naming authority identifier space associated with IANA
may be hierarchical and multi-leveled.

3.3.5 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 constraints of the
character encoding scheme.

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.
INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

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 unless they are escaped with the '\' character.
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.

urn <URN: Encoding_Scheme:Authority_Id : opaque_string >

Authority_Id Scheme_ID : [Individual ]
Scheme_ID IANA | ISBN_Publisher_ID | ISSN
Individual 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 | - | _ | . | @

The allowed characters in the opaque string are determined by the character
set encoding code. For the code ASCII, the allowable characters are xalphas as
above, the character ':' encoded as '\:', the character '>' encoded as '\>', and
the character '\' encoded as '\\'.

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

INTERNET--DRAFT Uniform Resource Names Weider, Deutsch

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

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