IETF URNbis WG                                                 J. Hakala
Internet-Draft                           The National Library of Finland
Obsoletes: 3188 (if approved)                             A. Hoenes, Ed.
Intended status: Standards Track                                  TR-Sys
Expires: June 25, 2011                                 December 22, 2010

     Using National Bibliography Numbers as Uniform Resource Names


   National Bibliography Numbers, NBNs, are widely used by the national
   libraries and other organizations in order to identify various
   resources such as monographs pre-dating the emergence of the ISBN
   system or still images.  NBNs are applied to all kinds of resources
   that do not have an established identifier system of their own.

   Since 2001, there has been a URN (Uniform Resource Names) namespace
   for NBNs, and during 2001-2009 millions of URN-based unique and
   persistent NBNs have been assigned.  The namespace registration was
   performed in RFC 3188 and applied to the NBNs known at that point.
   No URN:NBN resolution services existed at the time when the RFC was
   written.  Since then, several countries including Finland, Germany,
   Italy, and the Netherlands have used URN:NBNs to identify electronic
   resources and to provide persistent links to them.  To this end,
   these countries have established URN:NBN resolution services that
   supply URN - URL linking.

   This document replaces RFC 3188 and defines how NBNs can be supported
   within the URN framework.  An updated namespace registration is


   This document is an outcome of work performed in 2009-2010 as a part
   of the project PersID ( and brought into the
   IETF; it formally introduces the RFC 3188bis work from PersID as a
   chartered work item of the URNbis WG.

   Comments are welcome and should be directed to the
   mailing list or the authors.

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Status of This Memo

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   This Internet-Draft will expire on June 25, 2011.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Fundamental Namespace and Community Considerations . . . . . .  5
     3.1.  The URN:NBN Namespace  . . . . . . . . . . . . . . . . . .  5
     3.2.  Community Considerations for NBNs  . . . . . . . . . . . .  6
   4.  National Bibliography Numbers (NBNs) . . . . . . . . . . . . .  7
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Encoding Considerations and Lexical Equivalence  . . . . .  9
     4.3.  Resolution of NBN-based URNs . . . . . . . . . . . . . . . 11
     4.4.  Additional Considerations  . . . . . . . . . . . . . . . . 12
     4.5.  URN Namespace ID Registration for the National
           Bibliography Number (NBN)  . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Appendix A.  Draft Change Log  . . . . . . . . . . . . . . . . . . 21
     A.1.  draft-hakala-rfc3188bis-nbn-urn-00 to
           draft-ietf-urnbis-*-00 . . . . . . . . . . . . . . . . . . 21

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1.  Introduction

   One of the basic permanent URI schemes (cf. RFC 3986 [RFC3986],
   [IANA-URI]) is 'URN' (Uniform Resource Name) as originally defined in
   RFC 2141 [RFC2141] and now being formally specified in RFC 2141bis
   [I-D.ietf-urnbis-rfc2141bis-urn].  Any identifier, when used within
   the URN system, needs its own namespace.  As of this writing, there
   are roughly 40 registered URN namespaces (see [IANA-URN]), one of
   which belongs to NBN, National Bibliography Number, as specified 2001
   in RFC 3188 [RFC3188].

   Currently URN:NBNs are in production use in several European
   countries including (in alphabetical order) Austria, Finland,
   Germany, Italy, the Netherlands, Norway, Sweden, and Switzerland.
   Several other countries in Europe and elsewhere are considering usage
   of them.  URN:NBNs have been applied to, e.g., Web archives,
   digitized materials, and doctoral dissertations.

   As part of the validation process for the development of URNs back in
   the late 1990s, the IETF URN working group agreed that it was
   important to demonstrate that a 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 [RFC2288] investigated the feasibility
   of using three identifiers (ISBN, ISSN and SICI, see below) as URNs,
   with positive results; however, it did not formally register
   corresponding URN namespaces.  This was in part due to the still
   evolving process to formalize criteria for namespace definition
   documents and registration, consolidated later in the IETF into RFC
   3406 [RFC3406].  That RFC, in turn, is now being updated as well into
   RFC 3406bis [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg].

   URN Namespaces have subsequently been registered for NBN (National
   Bibliography Number), ISBN (International Standard Book Number), and
   ISSN (International Serial Standard Number) in RFCs 3188 [RFC3188],
   3187 [RFC3187], and 3044 [RFC3044], respectively.  However, there is
   no registered namespace for SICI (Serial Item and Contribution
   Identifier), and no plans to make such registration, due to the lack
   of use of that standard.  The ISBN namespace registration is being
   revised so that it covers both ISBN-10 and ISBN-13;
   [I-D.ietf-urnbis-rfc3187bis-isbn-urn].  The current ISSN registration
   still does not cover ISSN-L, defined in the new version of ISSN; the
   URNbis WG will provide an updated namespace registration in

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   Please note that NBN differs from the other identifiers listed above
   because it is not a single identifier system and there is no standard
   describing NBN systems in use.  The term "National Bibliography
   Number" encompasses all local identifier systems that the national
   libraries and their partner organizations use in addition to the more
   formally (and internationally) established identifiers.
   Historically, they were only applied in the national bibliographies
   to identify the resources catalogued into it.  During the last 10
   years, the NBN scope has been extended to cover a vast range of
   digital resources available via the Internet.  Only a minority of
   these resources are catalogued in the national bibliographies or
   other bibliographical databases.

   Guidelines for using NBNs as URNs and the original namespace
   registration have been published in RFC 3188 [RFC3188].  The RFC at
   hand replaces RFC 3188; sections discussing the methods in which URN:
   NBNs can be resolved have been updated and the text is also made
   compliant with the stipulations of RFC 3406bis
   [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg], the successor of RFC 3406
   [RFC3406], which previously had replaced RFC 2611 [RFC2611] that was
   applied in the initial registration.

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   NBN refers to any National Bibliography Number identifier system used
   by the national libraries and other institutions using the system
   with the national library's permission.

3.  Fundamental Namespace and Community Considerations

3.1.  The URN:NBN Namespace

   NBNs identify objects covered by legal requirements on national
   libraries and similar institutions to preserve the cultural
   inheritage of their constituents.  They are predominantly used for
   objects that have not been assigned other, more specific, standard
   identifiers that could be used to identfy them in catalogues and
   other collections of metadata.

   Therefore, to the same extent as NBNs are used to close gaps between
   existing, more universal, but also more specific, identifier systems
   (like ISBN and ISSN), a dedicated URN namespace is needed to map
   these identifiers into the URN system and thus make them actionable
   for URN resolution systems.

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   Section 4 below, and there in particular Section 4.1, presents a
   detailed overview of the structure of the NBN namespace, related
   institutions, and the identifier assignment principles used.

3.2.  Community Considerations for NBNs

   National libraries are the key organizations providing persistent URN
   resolution services for resources identified with NBNs, independent
   of their form.  National libraries may however allow other
   organizations such as university libraries or governmental
   organizations to assign NBNs to their resources.  In such case the
   national library will co-ordinate the use of NBNs and support the NBN
   users in guaranteeing the persistence of these resources and
   resolution.  These other organizations may establish their own
   resolution services or they may use the infrastructure provided by
   the national library.

   NBNs identify finite objects, but sometimes these objects might be so
   large or complex that identification of fragments is appropriate (in
   addition to identification of the resource itself).  The materials
   identified by an NBN will often be digital, but they may also exist
   only in printed or other physical form.  In such a case, the URN:NBN
   resolver should nevertheless be able to supply, e.g., a description
   of the resource, possibly including the address where the resource is

   National bibliography numbers enable the national libraries and
   organizations which liaise with them to uniquely identify resources
   and provide persistent links to the resource accessible in the
   Internet.  Since most digital documents held in national libraries'
   digital collections are not eligible for other, more formal
   identifiers such as ISBN, NBNs are a valuable asset for the
   community.  A proof of this are the millions of URN:NBNs that have
   been allocated since the NBN namespace was registered, and the
   operational services that have been built, using these identifiers
   and resolver applications.

   For library users, URN-based identification and resolution services
   mean more efficient and reliable access to resources.  No special
   tools are needed for this; Web browsers are sufficient.  The users
   may also be able to acquire URN:NBNs to their own works such as a
   university thesis.

   Section 4 below, and in particular Section 4.3 therein, presents a
   detailed overview of the application of the URN:NBN namespace and the
   principles, and systems used, for the resolution of NBN-based URNs.

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4.  National Bibliography Numbers (NBNs)

4.1.  Overview

   National Bibliography Number (NBN) is a generic name referring to a
   group of identifier systems administered by the national libraries
   and institutions authorized by them.  The NBN assignment is typically
   performed by the organization hosting the resource.  These
   organizations (national libraries and institutions in liaison with
   them) are usually committed to preserving their collections for a
   long time -- at least decades, and possibly centuries.  National
   libraries give NBNs to resources belonging to the (legal) deposit
   collections which by default will be kept as long as possible, but
   not to resources considered ephemeral.

   Each national library uses its own NBNs independently of other
   national libraries; there is no global authority that controls NBN
   usage.  For this reason, NBNs as such are unique only on a national
   level.  When used as URNs, NBN strings MUST be augmented with a
   controlled prefix such as the ISO 3166-1 alpha-2 two-letter country
   code.  These prefixes guarantee uniqueness of the NBN-based URNs on
   the global scale [Iso3166MA].

   NBNs have traditionally been given to documents that do not have a
   formal (standard) identifier, but are catalogued to the national
   bibliography.  Examples of this include books that predate the
   introduction of the ISBN in the 1970s, or modern books that for some
   reason have not received an ISBN.  NBNs can be seen as a fall-back
   mechanism: if no other, standards-based identifier such as an ISBN
   can be given, an NBN is assigned.

   URNs may also be used in universities' open repositories when a
   resource already has another identifier -- for instance, a Handle
   required by the open archive software, or a DOI (Digital Object
   Identifier) -- that can only be resolved in a publisher's (or third
   party's) resolution service.  Such persistent identifier cannot be
   used to provide linking to the open repository or legal deposit
   collection.  URN:NBN-based resolution can deliver that, and may also
   be extended to include access to other repositories holding the same

   In principle, NBNs enable identification of any kind of resource,
   such as still images published in periodical articles, or short
   stories and poems published in book form or in the Web. Local
   policies may limit the NBN usage to for instance documents stored
   permanently in the national library's collections.  Following the
   initial registration of a URN namespace for NBN, several countries
   broadened the scope of NBN assignment significantly to cover broader
   scope of their digital materials.

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   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 resources.
   There are also applications, used for instance in digitization
   processes, that assign NBNs automatically to resources or even their
   component parts such as still images published in monographs or

   Within the limitations set by RFC 2141[bis], this document, and other
   relevant RFCs, both syntax and scope of local NBNs can be decided by
   each national library independently.  Historically, NBNs have
   consisted of one or more letters and/or digits.  For instance,
   (Finnish) NBN for the Romanian translation of the Finnish classic
   "Seven Brothers" published in 1957 is f568471.  URN strings can
   contain encoded UNICODE characters, as specified in the declaration
   of syntactic structure, and there are no length limitations.
   Therefore, literally billions of NBNs can be allocated, which makes
   them suitable for, e.g., naming of Web documents.

   In Italy a novel hierarchical distributed architecture for NBN
   assignment has been designed, in order to eliminate the single-point-
   of-error risks of a centralised system and to reduce the costs of
   managing a resolution service based on persistent identifiers.

   The Central National Library in Florence manages the national domain
   NBN:IT and the national URN resolution service that contains every
   URN:NBN assigned in Italy.  The library has supplied URN:NBN:IT sub-
   domains to trusted institutions and bodies such as universities that
   are responsible for digital collections and routinely manage digital
   resources, for instance via creating and updating metadata on these
   resources, including location (URL) information.  All these
   institutions have their own resolution services, but the URN - URL
   mappings in them are periodically harvested to the national
   resolution service using the Open Archives Initiative Protocol for
   Metadata Harvesting (OAI-PMH; see

   Harvesting the data to the central node enables distributed service.
   The central node can serve the users when the local node is not
   functional.  This architecture increases the robustness of the
   network via duplication of resolution services and enables peer-to-
   peer resolution between the second-level institutions.  Moreover, it
   is possible to add yet another layer to the network by creating an
   international node, which shall contain all the data from the
   national nodes.  Such international service may also be created by
   building a virtual union resolver that uses all the national nodes.

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   The PersID project is implementing such a system at the European

4.2.  Encoding Considerations and Lexical Equivalence

   Embedding NBNs within the URN framework initially did not present any
   particular encoding problems, since the ASCII characters utilized in
   traditional NBN systems belonged to the URN character set.  Machine
   generated NBNs may be more demanding; if necessary, NBNs must be
   translated into canonical form as specified in RFC 2141bis

   When an NBN is used as a URN, the namespace-specific string must
   consist of three parts:

   o  a prefix, consisting of either a two-letter ISO 3166-1 country
      code or another registered string,

   o  a delimiting character that is either hyphen (-) or colon (:), and

   o  the NBN string.

   ISO 3166-1 country codes and other registered prefix strings are
   case-insensitive.  The NBN string may be case sensitive.

   Different delimiting characters are not lexically equivalent.

   A hyphen MUST be used for separating the prefix and the NBN string.

   A colon MAY be used as the delimiting character if and only if a
   country code-based NBN namespace is split further into smaller sub-

   If there are several national libraries in one country, these
   libraries can divide the national namespace between themselves using
   this method.

   A national library MAY also assign to trusted organization(s) such as
   a university or a government institution its own NBN sub-namespace.
   For instance, the national library of Finland has given Statistics
   Finland (<>) a sub-namespace "st"
   (i.e., urn:nbn:fi:st).  These trusted organizations must follow the
   general rules of the NBN usage provided by the national library, and
   take care of the long-term preservation of the identified resources
   in order to guarantee persistence.

   Sub-namespace identifier strings are case-insensitive.

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   Non-ISO 3166-1 alpha-2 prefixes, if used, MUST be registered on the
   global level.  The U.S. Library of Congress maintains the central
   register of assigned non-ISO 3166-1 prefix strings together with the
   name and contact information of the registrant.  Each prefix MUST
   have one and only one user organization, which is responsible for
   maintaining the delegated sub-namespace according to the general
   rules set out in this document.

      Since the setup of that registry, and up to the time of this
      writing, no such prefixes have been registered, and it is expected
      that demand will remain low.  Therefore, no more complicated rules
      (for instance for a hierarchical structure of such prefixes), are
      specified here.  For this unlikely case of unexpected future
      needs, a revision of this document would be needed to accommodate

      [[ Note: If the NBN community does not see a need to maintain this
      -- so far unused -- option for prefixes not based on ISO 3166-1,
      it could be dropped without breaking backwards compatibility.
      Another option to consider would be migrating the registry to IANA
      if that would be preferred by the Library of Congress. ]]

   Sub-namespace codes beneath a country-code-based namespace MUST be
   registered on the national level by the national library that
   assigned the code.  The national register of these codes SHOULD be
   made available online.

   All two-letter prefixes are reserved for existing and possible future
   ISO country codes (or for private use) [Iso3166MA] and MUST NOT be
   used as non-ISO country-code prefixes.  If there are several national
   libraries in one country that use the same country code as a shared
   prefix, they need to agree on how to divide the namespace.  They may
   either share one namespace but agree on how to avoid assigning
   duplicate identifiers, or they may split the namespace into library-
   specific sub-namespaces.

   Models (indicated linebreak inserted for readability):

      URN:NBN:<ISO 3166 alpha-2 country code>-<assigned NBN string>

      URN:NBN:<ISO 3166 alpha-2 country code>:<sub-namespace code>-\
          <assigned NBN string>

      URN:NBN:<non-ISO 3166 prefix>-<assigned NBN string>

   Examples (using actually assigned NBNs):

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   From the libraries' point of view, one of the key benefits of using
   URNs and other persistent identifiers is that there is only one
   location -- the resolution service -- where the linking infomation
   has to be maintained.  If bibliographic records in libraries' on-line
   public access catalogues (OPACs) contain URLs, then each record must
   be modified whenever the URL changes.  This may mean hundreds of
   changes for a popular resource.  With URNs, only the URN - URL
   linking in the mapping table of the resolution servicem needs to be
   kept up-to-date.  All links in the bibliographic records point to the
   resolution service where the URN is translated to one or more URL(s).

4.3.  Resolution of NBN-based URNs

   [[ Editorial Note: the text below needs to be revisited once the
   perspective of the list of URN services in RFC 2483 has been
   discussed and resolved by the WG. ]]

   URNs can be used to provide various services.  RFC 2483 [RFC2483]
   gives a few examples, such as retrieving a single URL or all URLs
   applying to the resource.  The constant development of digital
   library applications has widened the scope of the services needed,
   which has meant that RFC 2483 is becoming more outdated all the time.
   Resolution services available may vary from one URN resolver to the
   next, depending on the technical implementation of the resolver and
   the target system contacted.  Please note that services MUST NOT be
   hard coded into the URN itself when the identifier is assigned.

   Eventually, URN:NBNs will be resolved with the help of a resolver
   discovery service (RDS).  No such system has been installed yet in
   the Internet infrastructure.  Therefore, URN:NBNs should be embedded
   in HTTP URIs in order to make them actionable in the present
   Internet.  In these HTTP URIs, the authority part must point to the
   appropriate URN resolution service.  In Finland, the address of the
   national URN resolver is <>.  Thus the HTTP URI for the
   URN in the example is <>.
   This URL in turn resolves to the actual address of the thesis, which
   as of this writing (2010-03-27) was <

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   The country code-based prefix part of the URN namespace-specific
   string will provide a guide to finding the correct national
   resolution service for URN:NBNs from the resolver discovery service
   when it is established.  If there are multiple URN:NBN resolvers in
   the country, there are two possible approaches for making sure that
   RDS will work.  All URN:NBNs mappings can be harvested to the
   national node (the Italian approach).  The other approach is to make
   the RDS aware of all the URN:NBN resolution services, and specify in
   the RDS which parts of the national URN:NBN namespace they are
   capable of serving.

   URN:NBN - URL mappings maintained nationally can be harvested using,
   e.g., OAI-PMH from abroad to other national and international URN
   resolvers.  This makes it possible to improve the reliability of the
   system; if the Finnish national resolver node does not respond, its
   URN - URL mappings may be available at other resolvers.

   Persistence of any resolution service is not only a technical issue,
   but also an organizational and legal one.  National libraries are in
   ideal position to provide persistent resolution services, since most
   of them maintain (legal) deposit collections, in which domestic
   publications shall be preserved for future generations.  Increasingly
   these collection contain also digital resources.

4.4.  Additional Considerations

   Guidelines adopted and promoted by each national library define when
   different manifestations of a work should be assigned the same or
   differing NBNs.  But some simple guidelines should be followed by all
   users of the namespace.  Manifestations with significantly different
   semantic content -- following for instance a migration that failed to
   retain all content -- must not have the same NBN.  Manifestations
   that have the same content but different look and feel, or
   manifestations that look (almost) identical but have significant
   technical differences (such as the same text document as Word 2003
   file and OOXML file, or the same image as uncompressed TIFF and JPEG
   2000) should not have the same NBN.  If there are several copies of
   the file hosted by one organization, each copy must have the same
   NBN.  If the NBN is based on a checksum (such as MD5, see RFC 1321
   [RFC1321]), the resources that are identical at the bit level will
   receive the same NBN.  Dissimilar resources may in theory get the
   same checksum; with a reliable message digest algorithm such
   probability is however very small.

   The rules governing the usage of NBNs are local and usually less
   strict than those specifying the usage of ISBNs and other standard
   identifiers.  As long as the NBNs were assigned only in the national
   libraries, the identifier use was however well co-ordinated in

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   practice.  Now, following significant broadening in the scope of the
   NBN to cover Web resources, NBN assignment is less tightly
   controlled.  Works may have several manifestations that may be almost
   identical.  For instance, a single photo can published in many
   electronic newspapers in different countries.  Since there is no
   standard identifier for still images, such a photo is likely to
   receive multiple NBN, one in each national web archive.  Printed
   materials will also cause problems when dititized.  If two
   organizations are digitizing the same resources and use NBNs for
   identification of these resources, the result will be duplicate NBN
   assignment since NBNs as a rule have national scope, and these
   organizations may not be aware of each other.  If the metadata
   describing the resource is harvested into a common service, and the
   bibliographic records are similar enough to be merged, the user may
   see two NBNs and HTTP URIs pointing to two different resolution
   services and physical copies of the same resource.  If the two copies
   had the same identifier such as an ISBN, there would still be two
   HTTP URIs providing access to different physical copies of the
   resource since the locations of the resolution services will differ.

   If the same resource -- for instance, a master's thesis published by
   two universities -- is held in two repositories located in different
   NBN-sub-namespaces within one national namespace, these copies may
   also receive different NBNs especially if there is no easy way of
   checking if the resource has already been identified somewhere.  In
   this case, duplication may be revealed in the national level when the
   metadata records of the two copies are compared.  In such case, like
   in the previous example, both URN:NBNs are equally valid.

4.5.  URN Namespace ID Registration for the National Bibliography Number

   This registration describes how National Bibliography Numbers (NBNs)
   can be supported within the URN framework.

   [[ RFC Editor: please replace "XXXX" in all instances of "RFC XXXX"
      below by the RFC number assigned to this document. ]]

   Namespace ID:  NBN

      This Namespace ID was formally assigned to the National
      Bibliography Number in October 2001 when the namespace was
      registered officially.  Utilization of URN:NBNs started in
      demonstrator systems in 1998; since then, millions of URN:NBNs
      have been assigned.  The number of users of the namespace has
      grown in two ways: new national libraries have started using NBNs,
      and some national libraries already using the system have formed
      new liaisons.

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   Registration Information:

      Version: 4
      Date: 2010-12-22

   Declared registrant of the namespace:

      Name: Mr. Juha Hakala
      Affiliation: Senior Adviser, The National Library of Finland
      Postal: P.O.Box 15, 00014 Helsinki University, Finland
      Web URL:

      The National Library of Finland registered the namespace on behalf
      of the Conference of the European National Librarians (CENL) and
      Conference of Directors of National Libraries (CDNL), which have
      both made a commitment in 1998 to foster the use of URNs.  The NBN
      namespace is available for free for all national libraries in the
      world.  The national libraries may allow other organizations use
      the namespace for free or for a fee.

   Declaration of syntactic structure of NSS part:

      The namespace-specific string (NSS) will consist of three parts:

         a prefix, consisting of either an ISO 3166-1 alpha-2 country
         code or other registered string and sub-namespace codes,

         delimiting characters (colon (:) and hyphen (-)), and

         an NBN string assigned by the national library or sub-delegated

      Formal declaration of the NSS, using ABNF [RFC5234]:

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       nbn_nss     = prefix "-" nbn_string

       prefix      = cc_prefix / reg_prefix
                     ; these prefixes are case-insensitive

       cc_prefix   = iso_cc *( ":" subspc )

       iso_cc      = 2ALPHA
                     ; country code as assigned by ISO 3166, part 1 --
                     ; identifies the national library
                     ; to which the branch is delegated

       subspc      = 1*(ALPHA / DIGIT)
                     ; as assigned by the respective national library

       reg_prefix  = 3*(ALPHA / DIGIT)
                     ; as assigned by the Library of Congress --
                     ; identifies a trusted third party
                     ; to which the branch is delegated

       nbn_string  = <specific per prefix>
                     ; MUST adhere to RFC 3986 <path-rootless> syntax;
                     ; parsers must regard nbn_strings as case-sensitive

      Colon may be used as a delimiting character only within the
      prefix, between ISO 3166-1 country code and sub-namespace code(s),
      which split the national namespace into smaller parts.

      Dividing non-ISO 3166-based namespaces further with sub-namespace
      codes MUST NOT be done.

      Whereas all prefixes are regarded as case-insensitive, NBN-strings
      MAY be case-insensitive at the preference of the assigning
      authority; parsers therefore MUST treat these as case-sensitive;
      any case mapping needed to introduce case-insensitivity MUST be
      implemented in the responsible resolution system.

      Hyphen MUST be used as the delimiting character between the prefix
      and the NBN string.  Within the NBN string, hyphen MAY be used for
      separating different sections of the identifier 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, has beeen created and made available via the Web.
      Contact information: <>.

      All two-letter codes are reserved for existing and possible future
      ISO country codes and MUST NOT be used as non-ISO prefixes.

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      Sub-namespace codes MUST be registered on the national level by
      the national library that assigned the code.  The list of such
      codes SHOULD be available via the Web.

      Models (indicated linebreak inserted for readability):

         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>



   Relevant ancillary documentation:

      National Bibliography Number (NBN) is a generic name referring to
      a group of identifier systems used by the national libraries and
      other organizations for identification of deposited publications
      and other resources that lack a 'canonical' 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 neither a general standard
      defining NBN syntax nor a global authority to control the use of
      these identifier systems.

      Each national library decides locally which resources shall
      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.  With the introduction of the Internet and URN:
      NBN namespace in 1998, the scope of NBN assignment has been
      extended to a broad spectrum of Internet resources including,
      e.g., harvested Web pages.

      Some national libraries (Finland, Norway, Sweden) have established
      Web-based URN generators that enable authors and publishers to
      fetch NBN-based URNs for the resources they publish in the Web.
      The most significant group of publications to which NBNs have been
      applied are doctoral theses.

      The syntax of NBNs is decided by each national library
      independently.  Historically, NBNs used in national bibliographies
      contained only characters that belong to the URN character set.

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      Following the expansion of NBN scope and semi- and fully automated
      NBN assignment processes, some NBNs may contain characters that
      must be translated into canonical form according to the
      specifications in RFC 2141bis [I-D.ietf-urnbis-rfc2141bis-urn].

   Conformance with URN syntax:

      Traditional NBNs (those applied in the national bibliographies)
      consisted of ASCII 7-bit letters and digits (a-z and 0-9).  For
      instance, the NBN of the first Hungarian translation of the
      Finnish national epos Kalevala is f20043425.  The book was
      published in 1853 and therefore does not have an ISBN.  Machine-
      generated NBNs must follow the stipulations of RFC 2141bis

      [[ Editorial Note: Need to discuss new specification requirements
      from the RFC 2141bis draft! ]]

   Rules for lexical equivalence of NSS part:

      Two URN:NBNs are lexically equivalent if they are octet-by-octet
      equal after the following (conceptional) preprocessing:
      1. normalize the case of the leading "urn:" token
      2. normalize the case of the NID
      3. normalize the case of the NSS prefix
      4. normalize the case of any percent-encoding

      Note: The case used in the normalization steps is a local matter;
      implementations can normalize to lower or upper case as they see
      fit, they only need to do it consistently.

   Identifier uniqueness and persistence considerations:

      NBN strings assigned by two national libraries may be identical.
      In order to guarantee global uniqueness of NBN-based URNs,
      therefore a controlled prefix is present in the namespace specific
      string.  These NBNs, once given to the resource, will be
      persistent.  Persistence of the resources themselves will be
      guaranteed by the national libraries as a part of their legal
      deposit activities.  This applies to publications and Web
      resources only; long-term preservation of other resources such as
      governmental documents will be dependent on other actors like
      national archives.

      An NBN, once it has been assigned, must never be re-used for
      another resource.

      At the national level, libraries may utilise different policies

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      for guaranteeing uniqueness of NBNs.  They may be assigned
      sequentially by programs (URN generators) in order to avoid human
      mistakes.  It is also possible to use checksums such as SHA-1 or
      MD5 as NBN.

   Process of identifier assignment:

      Assignment of NBN-based URNs MUST be controlled on national level
      by the national library / national libraries.  Although the basic
      principles are the same, there are differences in scope; for
      instance in the Netherlands URN:NBNs are used -- among other
      things -- to identify scientific articles stored in the national
      library's long-term preservation system.  The National Library of
      Finland, on the other hand, is using URNs extensively to identify
      and provide access to the digitized content.  There are also
      organizations that use NBN-based URNs to identify data sets.  The
      common denominator, however, is that the identified resources
      themselves are persistent.

      National libraries may choose different strategies in assigning
      NBN-based URNs, and different approaches have varying levels of
      control with respect to the persistence of the documents.  Manual
      URN assignment by the library personnel only provides the best
      possible control, especially if this is done traditionally, that
      is, only when the document is catalogued into the national
      bibliography.  Usually the scope of URN:NBN is much broader than
      this; NBNs may for instance be automatically generated for each
      archived resource by a long-term preservation system.  From
      control point of view, the most liberal approach is a URN
      generator which builds URNs for everyone, with no guarantee that
      the resource identified will be preserved or accessible.  Every
      national library must decide the degree of freedom it allows to
      the URN:NBN users.  Usage rules may of course vary from one sub-
      namespace to the next.  As of yet there are no international
      guidelines for NBN use beyond what has been stipulated above, but
      more sttringent rules may be developed in the future.

   Process for identifier resolution:

      See Section 4.3 of RFC XXXX.

   Validation mechanism:

      None specified on the global level (beyond a routine check of
      those characters that require special encoding when employed in
      URIs).  A national library may use NBNs that contain a checksum
      and can therefore be validated, but as of this writing there are
      no NBNs which incorporate such checksum.

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      NBN is an umbrella referring to identifier systems used for
      identification of diverse publications and other resources in the
      national libraries and their partner organizations.

5.  Security Considerations

   This document proposes means of encoding NBNs within the URN
   framework.  A URN resolution service for NBN-based URNs is depicted,
   but only at a fairly generic level; thus, questions of secure or
   authenticated resolution mechanisms and authentication of users are
   out of scope of this document.  It does not deal with means of
   validating the integrity or authenticating the source or provenance
   of URNs that contain NBNs.  Issues regarding intellectual property
   rights associated with objects identified by the NBNs are also beyond
   the scope of this document, as are questions about rights to the
   databases that might be used to construct resolution services.

6.  IANA Considerations

   IANA is asked to update the existing registration of the Formal URN
   Namespace 'NBN' using the template given above in Section 4.5.

7.  Acknowledgements

   This document is an outcome of work performed in 2009-2010 as a part
   of the project PersID ( that aims at revising
   the basic URN RFCs, in order to bring them in alignment with the
   current URI Standard (STD 63, RFC 3986), ABNF, and IANA guidelines,
   and to establish a modern URN resolution system for bibliographic
   identifiers.  This work has been brought to the IETF and has lead to
   the establishment of the URNbis working group in the Applications
   Area.  The author wishes to thank his colleagues in the PersID
   project for their support.

   Your name could go here ...

8.  References

8.1.  Normative References

              Hoenes, A., "Uniform Resource Name (URN) Syntax",
              draft-ietf-urnbis-rfc2141bis-urn-00 (work in progress),
              November 2010.

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              Hoenes, A., "Uniform Resource Name (URN) Namespace
              Definition Mechanisms",
              draft-ietf-urnbis-rfc3406bis-urn-ns-reg-00 (work in
              progress), December 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

8.2.  Informative References

              Huttunen, M., Hakala, J., and A. Hoenes, "Using
              International Standard Book Numbers as Uniform Resource
              Names", draft-ietf-urnbis-rfc3187bis-isbn-urn-00 (work in
              progress), December 2010.

              IANA, "URI Schemes Registry",

              IANA, "URN Namespace Registry",

              ISO, "ISO Maintenance agency for ISO 3166 country codes",

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC2141]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC2288]  Lynch, C., Preston, C., and R. Jr, "Using Existing
              Bibliographic Identifiers as Uniform Resource Names",
              RFC 2288, February 1998.

   [RFC2483]  Mealling, M. and R. Daniel, "URI Resolution Services
              Necessary for URN Resolution", RFC 2483, January 1999.

   [RFC2611]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "URN Namespace Definition Mechanisms", BCP 33, RFC 2611,
              June 1999.

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   [RFC3044]  Rozenfeld, S., "Using The ISSN (International Serial
              Standard Number) as URN (Uniform Resource Names) within an
              ISSN-URN Namespace", RFC 3044, January 2001.

   [RFC3187]  Hakala, J. and H. Walravens, "Using International Standard
              Book Numbers as Uniform Resource Names", RFC 3187,
              October 2001.

   [RFC3188]  Hakala, J., "Using National Bibliography Numbers as
              Uniform Resource Names", RFC 3188, October 2001.

   [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "Uniform Resource Names (URN) Namespace Definition
              Mechanisms", BCP 66, RFC 3406, October 2002.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

Appendix A.  Draft Change Log

   [[ RFC-Editor: Whole section to be deleted before RFC publication. ]]

A.1.  draft-hakala-rfc3188bis-nbn-urn-00 to draft-ietf-urnbis-*-00

   - formal updates for a WG draft; no more "Updates: 2288";
   - introduced references to other URNbis WG documents;
   - changes based on review by Tommi Jauhiainen;
   - Sect. 3 restructured into namespace and community considerations;
   - old Sect. 7 incorporated in new Sect. 3.1;
   - Security Considerations: old Section 4.5 merged into Section 5;
   - added guidelines for when two manifestations of the same work
     should get different URN:NBNs;
   - clarified role of ISO 3166/MA for ISO 3166-1 country codes;
   - clarified role of non-ISO prefix registry maintaind by the LoC;
   - resolved inconsistency in lexical equivalence rules: as already
     specified for ISO alpha-2 country-codes, and in accordance with
     established practice, the whole NBN prefix is now declared case-
   - registration template adapted to rfc3406bis [-00];
   - numerous editorial fixes and enhancements.

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Authors' Addresses

   Juha Hakala
   The National Library of Finland
   P.O. Box 15
   Helsinki, Helsinki University  FIN-00014


   Alfred Hoenes (editor)
   Gerlinger Str. 12
   Ditzingen  D-71254


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