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IETF RFC 3187
Using International Standard Book Numbers as Uniform Resource Names
Last modified on Thursday, November 1st, 2001
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Network Working Group J. Hakala
Request for Comments: 3187 Helsinki University Library
Category: Informational H. Walravens
The International ISBN Agency
October 2001
Using International Standard Book 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 © The Internet Society (2001). All Rights Reserved.
Abstract
This document discusses how International Standard Book Numbers
(ISBN) can be supported within the URN (Uniform Resource Names)
framework and the syntax for URNs defined in RFC 2141. Much of the
discussion below is based on the ideas expressed in RFC 2288.
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.
Hakala & Walravens Informational PAGE 1 
RFC 3187 Using ISBNs as URNs October 2001
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 below.
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.
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RFC 3187 Using ISBNs as URNs October 2001
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 (http://www.isbn.spk-
berlin.de/html/prefix.htm). The group identifiers are listed at
http://www.isbn.spk-berlin.de/html/prefix/allpref.htm.
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.
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RFC 3187 Using ISBNs as URNs October 2001
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 (http://www.oclc.org ) 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.
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RFC 3187 Using ISBNs as URNs October 2001
Due to the intelligent structure of ISBN, group identifier or even
the publisher identifier can be used as a "hint". 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 following:
* 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
criteria:
* 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).
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RFC 3187 Using ISBNs as URNs October 2001
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 (ISBN)
This registration describes how International Standard Book Numbers
(ISBN) can be supported within the URN framework.
Namespace ID:
ISBN
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
Hakala & Walravens Informational PAGE 6
RFC 3187 Using ISBNs as URNs October 2001
Declared registrant of the namespace:
Name: Hartmut Walravens
E-mail: hartmut.walravens@sbb.spk-berlin.de
Affiliation: Director, The International ISBN Agency
Address: Staatsbibliothek zu Berlin - Preussischer 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.
Example:
URN:ISBN:0-395-36341-1
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 system.
Hakala & Walravens Informational PAGE 7
RFC 3187 Using ISBNs as URNs October 2001
* 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 identifiers.
* 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-berlin.de/html/userman.htm.
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
publication.
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.
Hakala & Walravens Informational PAGE 8
RFC 3187 Using ISBNs as URNs October 2001
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
ISBN.
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.
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RFC 3187 Using ISBNs as URNs October 2001
Validity of ISBN assignments can be checked from the group agencies
or directly from the publisher.
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.
7. Authors' Addresses
Juha Hakala
Helsinki University Library - The National Library of Finland
P.O. Box 26
FIN-00014 Helsinki University
FINLAND
EMail: juha.hakala@helsinki.fi
Hartmut Walravens
The International ISBN agency
Staatsbibliothek zu Berlin - Preussischer Kulturbesitz -
D-10772 Berlin
GERMANY
EMail: hartmut.walravens@sbb.spk-berlin.de
Hakala & Walravens Informational PAGE 10
RFC 3187 Using ISBNs as URNs October 2001
8. Full Copyright Statement
Copyright © The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Hakala & Walravens Informational PAGE 11
Using International Standard Book Numbers as Uniform Resource Names
RFC TOTAL SIZE: 22620 bytes
PUBLICATION DATE: Thursday, November 1st, 2001
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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