Network Working Group J. Hakala
Request for Comments: 3188 Helsinki University Library
Category: Informational October 2001
Using National Bibliography Numbers as
Uniform Resource Names
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document discusses how national bibliography numbers (persistent
and unique identifiers assigned by the national libraries) can be
supported within the URN (Uniform Resource Names) framework and the
syntax for URNs defined in RFC 2141. Much of the discussion is based
on the ideas expressed in RFC 2288.
1. Introduction
As part of the validation process for the development of URNs the
IETF working group agreed that it is important to demonstrate that
the current URN syntax proposal can accommodate existing identifiers
from well established namespaces. One such infrastructure for
assigning and managing names comes from the bibliographic community.
Bibliographic identifiers function as names for objects that exist
both in print and, increasingly, in electronic formats. RFC 2288
[Lynch] investigated the feasibility of using three identifiers
(ISBN, ISSN and SICI) as URNs.
This document will analyse the usage of national bibliography numbers
(NBNs) as URNs. The need to extend analysis to new identifier
systems was briefly discussed in RFC 2288 as well, with the following
summary: "The issues involved in supporting those additional
identifiers are anticipated to be broadly similar to those involved
in supporting ISBNs, ISSNs, and SICIs".
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A registration request for acquiring a Namespace Identifier (NID)
"NBN" for national bibliography numbers has been written by the
National Library of Finland on the request of the Conference of
Directors of National Libraries (CDNL) and the Conference of the
European National Librarians (CENL). Chapter 5 contains a URN
namespace registration request modeled according to the template in
RFC 2611.
The document at hand is part of a global co-operation of the national
libraries to foster identification of electronic documents in general
and utilisation of URNs in particular. Some national libraries,
including the national libraries of Finland, Norway and Sweden, are
already assigning NBN-based URNs for electronic resources.
We have used the URN Namespace Identifier "NBN" for the national
bibliographic numbers in examples below.
2. Identification vs. Resolution
As a rule the national bibliography numbers identify finite,
manageably-sized objects, but these objects may still be large enough
that resolution to a hierarchical system is appropriate.
The materials identified by a national bibliography number may exist
only in printed or other physical form, not electronically. The best
that a resolver will be able to offer in this case is bibliographic
data from a national bibliography database, including information
about where the physical resource is stored in a national library's
holdings.
The URN Framework provides resolution services that may be used to
describe any differences between the resource identified by a URN and
the resource that would be returned as a result of resolving that
URN. However, NBNs will be used for instance to identify resources
in digital Web archives created by harvester robot applications. In
this case, NBN will identify exactly the resource the user expects to
see.
3. National bibliography numbers
3.1 Overview
National Bibliography Number (NBN) is a generic name referring to a
group of identifier systems utilised by the national libraries and
only by them for identification of deposited publications which lack
an identifier, or to descriptive metadata (cataloging) that describes
the resources. In many countries legal (or voluntary) deposit is
being extended to electronic publications.
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Each national library uses its own NBN strings independently of other
national libraries; there is no global authority which controls them.
For this reason NBNs are unique only on national level. When used as
URNs, NBN strings must be augmented with a controlled prefix such as
country code. These prefixes guarantee uniqueness of the NBN-based
URNs on the global scale.
NBNs have traditionally been given to documents that do not have a
publisher-assigned identifier, but are cataloged to the national
bibliography. NBNs can be seen as a fall-back mechanism: if no
other, better established identifier such as ISBN can be given, an
NBN is assigned. In principle, NBN usage enables identification of
any Internet document. Local policies may limit the NBN usage to a
much smaller subset of documents.
Some national libraries (e.g., Finland, Norway, Sweden) have
established Web-based URN generators, which enable authors and
publishers to fetch NBN-based URNs for their network documents. At
least national libraries of Sweden and Finland are harvesting and
archiving domestic Web documents (and a number of other libraries
plan to start this activity), and long-time preservation of these
materials requires persistent and unique identification. NBNs can be
and are in fact already used as internal identifiers in these Web
archives.
Both syntax and scope of NBNs can be decided by each national library
independently. Typically, an NBN consist of one or more letters
and/or digits. This simple syntax makes NBNs infinitely extensible
and very suitable for e.g., naming of the Web documents. For
instance the application used by the national library of Finland for
Web harvesting creates NBNs which are based on the MD5 checksum of
the archived resource.
3.2 F-code
F-code is the NBN used by the National Library of Finland.
F-codes have been used since early 20th century to identify catalogue
cards and later MARC records in the national bibliography. In 1998
the national library decided to enable the Finnish authors and
publishers to assign F-codes to their Internet documents, if these
documents do not qualify for other identifiers such as ISBN. F-
codes, embedded into URNs, can be fetched from the URN generator
(http://www.lib.helsinki.fi/cgi-bin/urn.pl) developed in co-operation
between the national library of Finland and the Lund University
library, NETLAB unit. Attached to the generator there is a user
guide (http://www.lib.helsinki.fi/meta/URN-opas.html; only in
Finnish), which tells the users how to use URNs.
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F-codes are also used within the Web harvesting and archiving
software (http://www.csc.fi/sovellus/nedlib/), which has been built
for the Networked European Deposit Library (NEDLIB) project (see
http://www.kb.nl/nedlib). NEDLIB harvester calculates MD5 checksum
for each archived resource, and then builds an NBN-based URN from the
checksum. The URN serves then as a unique identifier to the archived
resource. Traditional identifiers can not be used for this purpose,
since there may for instance be several variants of a book which
(quite rightly so) all have the same ISBN. Moreover, identifiers
embedded into a document do not necessarily belong to the document
itself; thus the Web archiving application can not trust the
identifiers embedded into the body of the document.
The F-code built by the URN generator consist of:
Prefix (for example fe)
Year (YYYY; for example 1999)
Number (for example 1055)
The generator also adds namespace identifier "NBN" and ISO 3166
country code. Thus a URN based on F-code would in this case be for
instance urn:nbn:fi-fe19991055.
URNs created by the Web archiving application have similar overall
structure, except that prefix (which may be defined by the operator)
is fea and year is not used. An example: urn:nbn:fi-fea-
5c5875e6e49ae649cad63e5ee4f6c346.
F-codes never need any special encoding when used as URNs, since they
consist of alphanumeric codes only (0-9, a-z). This is often the
case for other national libraries' NBN systems as well.
3.3 Encoding Considerations and Lexical Equivalence
Embedding NBNs within the URN framework usually presents no
particular encoding problems, since all of the characters that can
appear in commonly used NBN systems can be expressed in special
encoding, as described in RFC 2141 [MOATS].
When an NBN is used as a URN, the namespace specific string will
consist of three parts: prefix, consisting of either a two-letter ISO
3166 country code or other registered string, delimiting character
which is either hyphen (-) or colon (:), and NBN string assigned by
the national library. Delimiting characters are not lexically
equivalent.
Hyphen is always used for separating the prefix and the NBN string.
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Colon is used as the delimiting character if and only if a country
code-based NBN namespace is split further in smaller sub-namespaces.
If there are several national libraries in one country, these
libraries can split their national namespace into smaller parts using
this method.
A national library may also assign a trusted organisation(s) its own
sub-namespace. For instance, the national library of Finland has
given Statistics Finland (http://www.stat.fi/index_en.html) a sub-
namespace "st" (e.g., urn:nbn:fi:st:). The Finnish Council of State
(http://www.vn.fi/vn/english/index.htm) will use sub-namespace "vn"
(e.g., urn:nbn:fi:vn).
Non-ISO 3166-prefixes, if used, must be registered on the global
level. The Library of Congress will maintain the central register of
reserved codes. This register will be available to the national
libraries and other users in the Web.
Sub-namespace codes beneath a country-code-based namespace need to be
registered on the national level by the national library which
assigned the code. The national register must be available in the
Web and should also be linked to the global register maintained by
the Library of Congress.
Two-letter codes may not be used as non-ISO prefixes, since all such
codes are reserved for existing and possible future ISO country
codes. If there are several national libraries in one country who use
the same prefix - for instance, a country code -, they need to agree
on how to split the namespace between them.
Models:
URN:NBN:<ISO 3166 country code>-<assigned NBN string>
URN:NBN:<ISO 3166 country code>:<sub-namespace code>-<assigned NBN
string>
URN:NBN:<non-ISO 3166 prefix>-<assigned NBN string>
Examples:
URN:NBN:fi-fe19981001 (A "real" URN assigned by the National Library
of Finland).
3.4 Resolution of NBN-based URNs
The (usually) country code-based prefix part of the URN namespace
specific string will provide a guide to where to find a resolution
service, and the NBN register will identify the assigning agency.
Once the NBN-based URN resolution is in global usage, the number of
prefixes will slowly approach and may eventually exceed the number of
national libraries.
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If NBN assignment for a given country is limited to the national
bibliography database, then all NBN-based URNs for that country will
be resolved there. In one model these databases contain detailed
resource descriptions including URLs, which will point both to the
copy of the document in the Internet and to the copy in the national
library's (legal) deposit collection. Due to the limitations in the
usage of legal deposit documents it is possible that the deposited
electronic materials can not be delivered in electronic form outside
the premises of the national library.
If it is possible for the authors and publishers to retrieve NBNs to
Web documents and there is no obligation to deposit thus identified
documents to the national library, URN resolution service is not
possible without a national Web index and archive, maintained by the
national library or other organisation(s). A Web index/archive will
also resolve machine-generated URNs to the archived Web documents.
3.5 Additional considerations
Guidelines adopted by each national library define when different
versions of a work should be assigned the same or differing NBNs.
These rules apply only if identifier assignment is done manually. If
identifiers are allocated programmatically, the only criteria that
can be used is that two documents which are identical on the bit
level (have the same MD5 checksum) are deemed identical and should
receive the same NBN. The likelihood of this happening to dissimilar
documents is about 2^64, according to the RFC 1321.
The rules governing the usage of NBNs are less strict than those
specifying the usage of ISBN or other, better established
identifiers. Since the NBNs have up to now been given only by the
personnel (cataloguers) working in the national libraries, the
identifier assignment has in practice been well co-ordinated.
A NBN-based URN will resolve to single instance of the work if
identifier assignment has been automatic. Given the nature of NBNs
it is also likely that different versions of the same work will
receive different NBNs even if the identifier is given manually.
4. Security Considerations
This document proposes means of encoding several existing
bibliographic identifiers within the URN framework. This document
does not discuss resolution except at a very generic level; thus
questions of secure or authenticated resolution mechanisms are out of
scope. It does not address means of validating the integrity or
authenticating the source or provenance of URNs that contain
bibliographic identifiers. Issues regarding intellectual property
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rights associated with objects identified by the various
bibliographic identifiers are also beyond the scope of this document,
as are questions about rights to the databases that might be used to
construct resolvers.
5. Namespace registration
URN Namespace ID Registration for the National Bibliography Number
(NBN)
Namespace ID:
NBN
This Namespace ID has been in production use in demonstrator systems
since summer 1998; thousands of URNs from this namespace have already
been delivered in Finland, Sweden and Norway.
Registration Information:
Version: 3
Date: 2001-01-30
The first registration of the NID "NBN" was done via the URN WG in
1998. The second, slightly edited registration request was done in
1999.
Declared registrant of the namespace:
Name: Juha Hakala
E-mail: juha.hakala@helsinki.fi
Affiliation: Helsinki University Library - The National Library of
Finland, Conference of European National Librarians (CENL) and
Conference of Directors of National Libraries (CDNL)
Address: P.O.Box 26, 00014 Helsinki University, Finland
Both CENL and CDNL made decisions to foster the usage of URNs during
1998. The latter organisation has set up a working group for this
purpose. One item in the common work plan is utilisation of national
bibliography numbers as URNs for identification of grey literature
published in the Internet. The NBN namespace will be available for
free for all national libraries in the world.
Declaration of syntactic structure:
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The namespace specific string will consist of three parts:
prefix, consisting of either a two-letter ISO 3166 country code or
other registered string and sub-namespace codes,
delimiting characters (colon (:), or hyphen (-), and
NBN string assigned by the national library.
Colon is used as a delimiting character only within the prefix,
between ISO 3166 country code and sub-namespace code, which splits
the national namespace into smaller parts. This technique can be
used when there are several national libraries, which all need their
own namespaces, or when the national library allows trusted partners
to set up their own sub-namespaces within the national NBN namespace.
Dividing non-ISO 3166-based namespaces further with sub-namespace
codes is not allowed.
Hyphen is used as a delimiting character between the prefix and the
NBN string. Within the NBN string, hyphen can be used for separating
different sections of the code from one another.
Non-ISO prefixes used instead of the ISO country code must be
registered. A global registry, maintained by the Library of
Congress, will be created and made available via the Web. Contact
information: nbn.register@loc.gov.us.
All two-letter codes are reserved for existing and possible future
ISO country codes and may not be used as non-ISO prefixes.
Sub-namespace codes must be registered on the national level by the
national library which assigned the code. The register must be
available via the Web, and it should be accessible via the global
registry set up by the Library of Congress.
Models:
URN:NBN:<ISO 3166 country code>-<assigned NBN string>
URN:NBN:<ISO 3166 country code:sub-namespace code>-<assigned NBN
string>
URN:NBN:<non-ISO 3166 prefix>-<assigned NBN string>
Example:
A country code-based URN: URN:NBN:fi-fe19981001 (A URN assigned by
the National Library of Finland).
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Relevant ancillary documentation:
National Bibliography Number (NBN) is a generic name referring to a
group of identifier systems used by the national libraries for
identification of deposited publications which lack an identifier, or
to descriptive metadata (cataloguing) that describes the resources.
Each national library uses its own NBN system independently of other
national libraries; there is no global authority which controls
syntax of these identifier systems.
Each national library can decide freely which resources will receive
NBNs. These identifiers have traditionally been assigned to
documents that do not have a publisher-assigned identifier, but are
nevertheless catalogued to the national bibliography. Typically
identification of grey publications have largely been dependent on
NBNs.
Some national libraries (Finland, Norway, Sweden) have established
Web-based URN generators, which enable authors and publishers to
fetch NBN-based URNs for their network documents.
Both syntax and scope of NBNs is decided by each national library
independently. Typically, a NBN consist of one or more letters and a
number.
Identifier uniqueness considerations:
NBN strings assigned by two national libraries may be identical. For
this reason usage of a controlled prefix in the namespace specific
string is obligatory in order to guarantee global uniqueness of NBN-
based URNs.
In the national level, libraries utilise different policies for
guaranteeing uniqueness. A national library may automate the
delivery of NBN-based URNs. In this case, the NBNs are assigned
sequentially by a program (URN generator).
Identifier persistence considerations:
Persistence of the NBNs as identifiers is guaranteed by the
persistence of national libraries and information systems, such as
national bibliographies, maintained by them. NBNs have been used for
several centuries for printed materials. NBN-based identification of
electronic documents is a recent practice, but it is likely to
continue for a very long time.
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Process of identifier assignment:
Assignment of NBN-based URNs is always controlled on national level
by the national library / national libraries. The Conference of
Directors of National Librarians (CDNL) has established in 1999 a
task force, which will co-ordinate the URN usage in all national
libraries.
National libraries may choose different strategies in assigning NBN-
based URNs. One option is assignment by the library personnel only.
This is done when the document is catalogued into the national
bibliography. Thus in this case the national bibliography database
will serve as the URN resolution service.
A national library may also set up a URN generator (generators), and
allow publishers and authors to retrieve NBN-based URNs from there.
In this case there is no guarantee that the identified resource will
ever be catalogued into the national bibliography, and URN resolution
is dependent on Web index/archive.
Process for identifier resolution:
URNs based on NBNs will be primarily resolved via the national
bibliography databases. In one model these databases contain
detailed resource descriptions including URLs, which will point both
to the copy of the document in the Internet and to the copy in the
national library's (legal) deposit collection. Due to the
limitations in the usage of legal deposit documents it is possible
that the deposited materials can not be delivered outside the
premises of the national library.
For those documents not catalogued into the national bibliography
database URN resolution may take place via national or international
Web indexes and/or archives. Nordic national libraries have
established in autumn 2000 a joint initiative called Nordic Web
Archive (NWA), which aims at creating a national Web archive into all
Nordic countries. Indexes to these archive systems will be able to
act as URN resolution services of any document which a) is or has
been available via the Web, and b) had an URN embedded into it.
Country code and additional sub-namespace information will provide a
guide to where to find appropriate resolution services. For
instance, if the country code is "fi", the primary resolution service
is the national bibliography database. Secondary resolution service
is the Web archive.
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Generally, there will be one or more resolution services specified
for each country, depending on the assignment policy and services of
the national library. If NBN assignment is limited to the national
bibliography database, then all NBN-based URNs for that country will
be resolved there. If the authors and publishers have been allowed
to retrieve NBNs to their Web resources, URN resolution services
require a national Web archive. If other organisations have been
allowed to assign NBNs, they may also set up their own URN resolution
services.
Rules for Lexical Equivalence:
None in the global level. Any national library may provide its own
rules, on the basis of its NBN syntax.
Conformance with URN Syntax:
All NBNs we know of are ASCII strings consisting of letters (a-z) and
numbers (0-9). If NBN contains characters that are reserved in the
URN syntax, this data must be presented in hex encoded form as
defined in RFC 2141. A national library may limit the full scope of
its NBN strings in URN usage in such a way that there are no reserved
characters in the URN namespace specific strings.
Validation mechanism:
None specified on the global level. A national library may use NBNs,
which contain a checksum and can therefore be validated, but this is
for the time being not a common practice.
Scope:
Global.
6. References
[Daigle] Daigle, L., van Gulik, D., Iannella, R. and P. Faltstrom,
"URN Namespace Definition Mechanisms", RFC 2611, June 1999.
[Lynch] Lynch, C., Preston, C. and R. Daniel, "Using Existing
Bibliographic Identifiers as Uniform Resource Names", RFC
2288, February 1998.
[Moats] Moats, R., "URN Syntax", RFC 2141, May 1997.
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7. Author's Address
Juha Hakala
Helsinki University Library - The National Library of Finland
P.O. Box 26
FIN-00014 Helsinki University
FINLAND
EMail: juha.hakala@helsinki.fi
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