Internet DRAFT - draft-hakala-isbn


Network Working Group                                       Juha Hakala
Internet-Draft                              Helsinki University Library
Category: Informational                               Hartmut Walravens
draft-hakala-isbn-01.txt                  The International ISBN Agency
Expires: 25 July 2001                                   25 January 2001

                Using International Standard Book Numbers as
                         Uniform Resource Names

Status of this Memo

This document is an Internet-Draft and is in full conformance with all 
provisions of Section 10 of RFC2026.

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This Internet-Draft will expire on 25 January, 2001.


This document discusses how International Standard Book Numbers (ISBN) 
can be supported within the URN framework and the syntax for URNs 
defined in RFC 2141 [Moats. Much of the discussion below is based on the 
ideas expressed in RFC 2288 [Lynch]. Chapter 5 contains a URN namespace 
registration request modelled according to the template in RFC 2611 
[Daigle et al.].

1. Introduction 

As part of the validation process for the development of URNs the IETF 
URN 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 et. al.] 
investigated the feasibility of using three identifiers (ISBN, ISSN and 
SICI) as URNs. This document will analyse the usage of ISBNs as URNs in 
more detail than RFC 2288. 

A registration request for acquiring Namespace Identifier (NID) "ISBN" 
for ISBNs is included in chapter 5. 

The document at hand is part of a global joint venture of the national 
libraries to foster identification of electronic documents in general 
and utilisation of URNs in particular. The document was written as a co-
operative project between the Helsinki University Library and The 
International ISBN Agency. 

We have used the URN Namespace Identifier "ISBN" for ISBNs in examples 

2. Identification vs. Resolution

As a rule the ISBNs identify finite, manageably-sized objects, but these 
objects may still be large enough that resolution into a hierarchical 
system is appropriate.

The materials identified by an ISBN 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 the national library's holdings. 

3. International Standard Book Numbers

3.1 Overview

RFC 2288 [Lynch] describes the ISBN system in the following way:

   An International Standard Book Number (ISBN) identifies an edition of
   a monographic work.  The ISBN is defined by the standard
   NISO/ANSI/ISO 2108:1992 [ISO1]

   Basically, an ISBN is a ten-digit number (actually, the last digit
   can be the letter "X" as well, as described below) which is divided
   into four variable length parts usually separated by hyphens when
   printed.  The parts are as follows (in this order):

   * a group identifier which specifies a group of publishers, based on
   national, geographic or some other criteria,

   * the publisher identifier,

   * the title identifier,

   * and a modulus 11 check digit, using X instead of 10.

   The group and publisher number assignments are managed in such a way
   that the hyphens are not needed to parse the ISBN unambiguously into
   its constituent parts.  However, the ISBN is normally transmitted and
   displayed with hyphens to make it easy for human beings to recognize
   these parts without having to make reference to or have knowledge of
   the number assignments for group and publisher identifiers.

Groups usually cover only one country, but occasionally a single group is used 
in several countries. For instance, group "3" is utilised in Germany, Austria 
and German-speaking parts of Switzerland. "976" is used in Caribbean community 
(Antigua, Bahamas, Barbados, Belize, Cayman Islands, Dominica, Grenada, Guyana, 
Jamaica, Montserrat, St. Kitts-Nevis, St. Lucia, St. Vincent and the Grenadines, 
Trinidad and Tobago, Virgin Islands (Br))and "982" in South Pacific (Cook 
Islands, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Solomon Islands, 
Tokelau, Tonga, Tuvalu; Vanuatu, Western Samoa). For each international group, 
the International ISBN Agency has assigned ranges of publisher identifiers to 
individual countries. These ranges are listed on the ISBN web site 
( The group identifiers are 
listed at

There are plans to extend the ISBN into 13 digits in order to make the 
system more suitable for identification of electronic monographs. So 
called Bookland ISBN will consist of a traditional ISBN preceded by the 
978 or 979 EAN flag.

3.2 Encoding Considerations and Lexical Equivalence

RFC 2288 [Lynch] says that:

   Embedding ISBNs within the URN framework presents no particular
   encoding problems, since all of the characters that can appear in an
   ISBN are valid in the identifier segment of the URN.  %-encoding, as
   described in [MOATS] is never needed.

   Example: URN:ISBN:0-395-36341-1

   For the ISBN namespace, some additional equivalence rules are
   appropriate.  Prior to comparing two ISBN URNs for equivalence, it is
   appropriate to remove all hyphens, and to convert any occurrences of
   the letter X to upper case.

3.3 Resolution of ISBN-based URNs

The existing ISBN structure is suitable for URN resolution purposes. The 
group identifier can assist in the resolver discovery process. For 
instance, the group identifier "951" means Finland. In this case, the 
Finnish national bibliographic database will be able to resolve the URN 
either into bibliographic data or - if the resource is available in the 
Internet - to the document itself.

If a group identifier does not identify a single country but a language 
area, there are two means for locating the correct national 
bibliography. First, it is possible to define a cascade of URN 
resolution services - for instance, German national bibliography, 
Austrian national bibliography and Swiss national bibliography, in this 
order - into the DNS records describing the resolution service for ISBNs 
starting with "3". Second, the publisher identifier ranges assigned by 
the International ISBN Agency could be defined into the DNS records. 
This method is better than cascading, since the correct resolution 
service can be found immediately.

In some exceptional cases - notably in the US and in UK, where 
international companies do a significant portion of publishing - the 
information provided by the group identifier may not always be fully 
reliable. For instance, some monographs published in New York by 
international publishing companies may get an ISBN with the group 
identifier "3". This is technically appropriate when the headquarters or 
one of the offices of the publisher is located in Germany. Information 
about such a book will not be available in the German national 
bibliography, but via the Library of Congress systems. Unfortunately the 
appropriate national bibliography cannot be known to the resolver 
discovery service. 

As a fall back mechanism a large union catalogue, such as WorldCat 
maintained by OCLC ( ) could be used to complement 
the default services provided by national bibliographies.

The problem described above may well be less severe than it looks. Some 
international publishers (Springer, for example) give the whole 
production to the national library of their home country as legal 
deposit, no matter which country the book was published. Thus everything 
published by Springer in New York with group identifier "3" will be 
found from the German national bibliography. On the other hand, when 
these companies give their home base also as a place of publication, the 
"home" national library requires the legal deposit. 

Due to the intelligent structure of ISBN, group identifier or even the 
publisher identifier can be used as a ćhintĆ. Technically it is possible 
to incorporate into the common structure also URN resolution services 
maintained by publishers. For instance, "951-0" is the unique ISBN 
publisher identifier of the largest publisher in Finland, Sanoma-WSOY. 
If they launch their own URN resolution services, resolution requests 
for ISBNs starting with "951-0" will be directed to the publisher's 
server, and all other requests to the national bibliography. 

3.4 Additional considerations

The basic guidelines for assigning ISBNs to electronic resources are the 

* Format/means of delivery is irrelevant to the decision whether a 
product needs an ISBN or not. If the content meets the requirement, it 
gets an ISBN, no matter what the format of the delivery system.

* Each format of a digital publication should have a separate ISBN. 

The definition of a new edition is normally based on one of the two 

* A change in the kind of packaging involved: the hard cover edition, 
the paperback edition and the library-binding edition would each get a 
separate ISBN. The same applies to different formats of digital files.

* A change in the text, excluding packaging or minor changes such as 
correcting a spelling error. Again, this criterion applies regardless of 
whether the publication is in printed or in digital form.  

Although these rules seem very clear, their interpretation may vary. As 
[Lynch] points out,

   The choice of whether to assign a new ISBN or to
   reuse an existing one when publishing a revised printing of an
   existing edition of a work or even a revised edition of a work is
   somewhat subjective.  Practice varies from publisher to publisher
   (indeed, the distinction between a revised printing and a new edition
   is itself somewhat subjective).  The use of ISBNs within the URN
   framework simply reflects these existing practices.  Note that it is
   likely that an ISBN URN will often resolve to many instances of the
   work (many URLs).

Publishers have also in some occasions re-used the same ISBN for another 
book. This reasonably rare kind of human error does not threaten or 
undermine the value of the ISBN system as a whole. Neither do they pose 
a serious threat to the URN resolution service based on ISBNs. An error 
will only lead into the retrieval of two or more bibliographic records 
from a national bibliographic database. Based on the information in the 
records, a user can choose the correct record from the result set. 

Most national bibliographies and especially the Books in Print correct 
ISBN mistakes. The systems then provide cross references ("incorrect 
ISBN -> correct ISBN"). 

Further details on the process of assigning ISBNs can be found in 
section 5  (Namespace registration) below.

4. Security Considerations

This document proposes means of encoding ISBNs within the URN framework. 
ISBN-based URN resolution service is depicted here only in a fairly 
generic level; thus questions of secure or authenticated resolution 
mechanisms are excluded.  It does not deal with means of validating the 
integrity or authenticating the source or provenance of URNs that 
contain ISBNs.  Issues regarding intellectual property rights associated 
with objects identified by the ISBNs 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 International Standard Book Number 

This registration describes how International Standard Book Numbers 
(ISBN) can be supported within the URN framework. 

Namespace ID:


This Namespace ID is the same as the internationally known acronym for 
the International Standard Book Number. Giving NID "ISBN" to any other 
identifier system would cause a lot of confusion.

Registration Information:

Version: 1
Date: 2001-01-25

Declared registrant of the namespace:

Name: Hartmut Walravens
Affiliation: Director, The International ISBN Agency
Address: Staatsbibliothek zu Berlin - Preužischer Kulturbesitz - D-10772 
Berlin, Germany

Declaration of syntactic structure:

An ISBN is a ten-digit number (actually, the last digit can be the 
letter "X" as well, as described below) which is divided into four 
variable length parts usually separated by hyphens when printed.  The 
parts are as follows (in this order):

* a group identifier which specifies a group of publishers, based on 
national, geographic or some other criteria,

* the publisher identifier,

* the title identifier,

* and a modulus 11 check digit, using X instead of 10.



Relevant ancillary documentation:

The ISBN (International Standard Book Number) is a unique machine-
readable identification number, which marks any edition of a book 
unambiguously. This number is defined in ISO Standard 2108. The number 
has been in use now for 30 years and has revolutionised the 
international book-trade. 154 countries are officially ISBN members, and 
more countries are joining the system. 

The administration of the ISBN system is carried out on three levels: 

   International agency
   Group agencies
   Publisher levels

The International ISBN agency is located within the State Library 
Berlin. The main functions of the International ISBN Agency are: 

* To promote, co-ordinate and supervise the world-wide use of the ISBN 
* To approve the definition and structure of group agencies.
* To allocate group identifiers to group agencies.
* To advise on the establishment and functioning of group agencies.
* To advise group agencies on the allocation of international publisher 
* To publish the assigned group numbers and publishers prefixes in up-
to-date form. 

More information about ISBN usage can be found from the ISBN Users' 
Manual. 4th edition of this document is available at http://www.isbn.spk-

Identifier uniqueness considerations:

ISBN that has been assigned once should never be re-used. Nevertheless, 
publishers do occasionally re-use the same number. From the point of the 
URN resolution system proposed here, this will typically cause retrieval 
of two bibliographic records. A user can choose the correct publication 
using the data in the record, such as the author or title. 

Incorrect ISBNs are routinely corrected in national bibliographies and 
Books in Print catalogue.

Identifier persistence considerations:

The ISBN accompanies a publication from its production onwards. It is 
persistent; ISBN once given - if correct - will never leave the 

Identifier assignment process:

Assignment of ISBNs is always controlled by ISBN group agencies, which 
are often national and quite frequently located in the national 
libraries. Publishers are usually given blocks of ISBNs, from which they 
pick identifiers for their newly published items. 

As pointed out earlier, in spite of the common rules of how to use 
ISBNs, there is some variation between different publishers in ISBN 
assignment. In practice these differences are so small that they do not 
pose a threat to the usability of the ISBN system.

Identifier resolution process:

URNs based on ISBNs will be primarily resolved via the national 
bibliography databases. Since ISBN group agencies are as a rule located 
in national libraries, the national bibliography databases cover almost 
every publication which does have an ISBN. 

If group identifier does not define a country but a language area there 
may be many countries using the same group identifier. In such cases, 
the International ISBN Agency has divided publisher identifiers into 
ranges assigned to each country within the group. The appropriate 
resolution service can be found by using the group identifier and 
publisher identifier information. Alternatively a cascade of national 
bibliographies can be defined. 

Resolution carried out in national bibliography databases may be 
complemented by so called union catalogues, which contain huge amount of 
bibliographic data (up to 42 million records). This complementary 
service is only needed if the ISBN group identifier information is 
misleading. This is not common.

The International ISBN Agency maintains a list of publishers who have 
been assigned a publisher identifier within the ISBN system. The 
publisher identifier may be used to allow participation of resolution 
services maintained by publishers into the URN resolution system for 

Rules for Lexical Equivalence:

For the ISBN namespace, some additional equivalence rules are 
appropriate.  Prior to comparing two ISBN URNs for equivalence, it is 
appropriate to remove all hyphens, and to convert any occurrences of the 
letter X to upper case.

Conformance with URN Syntax:

Embedding ISBNs within the URN framework presents no particular encoding 
problems, since all of the characters that can appear in an ISBN are 
valid in the identifier segment of the URN %-encoding, as described in 
[MOATS] is never needed.

   Example: URN:ISBN:0-395-36341-1

Validation mechanism:

Validity of an ISBN string can be checked by modulus 11 check digit, 
included in the ISBN. X is used instead of 10.

Validity of ISBN assignments can be checked from the group agencies or 
directly from the publisher. 



6. References

[Daigle et al.]: Daigle, L., van Gulik, D., Iannella, R. & Faltstrom, 
P.: URN Namespace Definition Mechanisms, RFC2611, June 1999.
[Lynch] Lynch, C., Using Existing Bibliographic Identifiers as Uniform 
Resource Names, RFC 2288, February 1998
[Moats] Moats, R., "URN Syntax", RFC 2141, May 1997.

7. Authors' Addresses

   Juha Hakala
   Helsinki University Library - The National Library of Finland
   P.O. Box 26
   FIN-00014 Helsinki University

...Hartmut Walravens
   The International ISBN agency
   Staatsbibliothek zu Berlin - Preužischer Kulturbesitz -
   D-10772 Berlin,

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