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RFC 3187

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Using International Standard Book Numbers as Uniform Resource Names


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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 (C) The Internet Society (2001).  All Rights Reserved.


   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.

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   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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      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-  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.

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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

   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

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   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

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

   *  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

   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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   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:


   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

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   Declared registrant of the namespace:

   Name: Hartmut Walravens
   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.



   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.

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   *  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

   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.

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   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.

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



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


   Hartmut Walravens
   The International ISBN agency
   Staatsbibliothek zu Berlin - Preussischer Kulturbesitz -
   D-10772 Berlin


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8. Full Copyright Statement

   Copyright (C) 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

   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


   Funding for the RFC Editor function is currently provided by the
   Internet Society.