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rfc:rfc8458

Internet Engineering Task Force (IETF) J. Hakala Request for Comments: 8458 The National Library of Finland Obsoletes: 3188 October 2018 Category: Informational ISSN: 2070-1721

   Using National Bibliography Numbers as Uniform Resource Names

Abstract

 National Bibliography Numbers (NBNs) are used by national libraries
 and other organizations in order to identify resources in their
 collections.  NBNs are usually applied to resources that are not
 catered for by established (standard) identifier systems such as
 International Standard Book Number (ISBN).
 A Uniform Resource Name (URN) namespace for NBNs was established in
 2001 in RFC 3188.  Since then, a number of European national
 libraries have implemented URN:NBN-based systems.
 This document replaces RFC 3188 and defines how NBNs can be supported
 within the updated URN framework.  A revised namespace registration
 (version 4) compliant to RFC 8141 is included.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are candidates for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8458.

Hakala Informational [Page 1] RFC 8458 NBN URNs October 2018

Copyright Notice

 Copyright (c) 2018 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Conventions Used in This Document . . . . . . . . . . . . . .   5
 3.  Fundamental Namespace and Community Considerations for NBN  .   5
   3.1.  The URN:NBN Namespace . . . . . . . . . . . . . . . . . .   5
   3.2.  Community Considerations for NBNs . . . . . . . . . . . .   6
 4.  National Bibliography Number URNs . . . . . . . . . . . . . .   7
   4.1.  Assignment  . . . . . . . . . . . . . . . . . . . . . . .   7
   4.2.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.1.  Usage of r-component and q-component  . . . . . . . .  10
     4.2.2.  Usage of f-component  . . . . . . . . . . . . . . . .  10
   4.3.  Encoding Considerations and Lexical Equivalence . . . . .  10
   4.4.  Resolution and Persistence of NBN-based URNs  . . . . . .  12
   4.5.  Additional Considerations . . . . . . . . . . . . . . . .  13
 5.  URN Namespace ID (NID) Registration for the National
     Bibliography Number (NBN) . . . . . . . . . . . . . . . . . .  13
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
 7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
   8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
 Appendix A.  Significant Changes from RFC 3188  . . . . . . . . .  18
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

Hakala Informational [Page 2] RFC 8458 NBN URNs October 2018

1. Introduction

 One of the basic permanent Uniform Resource Identifier (URI) schemes
 (cf. [RFC3986] and [IANA-URI]) is Uniform Resource Name (URN).  URNs
 were originally defined in RFC 2141 [RFC2141].  In 2017, a revision
 was adopted with new definitions and registration procedures
 [RFC8141].  Any traditional identifier, when used within the URN
 system, must have a namespace of its own that is registered with IANA
 [IANA-URN].  National Bibliography Number (NBN) is one such
 namespace, specified in 2001 in RFC 3188 [RFC3188].
 This document describes the syntax and usage of NBN URNs and updates
 the registration of the associated URN namespace.  This document
 additionally describes certain policy assumptions about how national
 libraries and their partner organizations partition, delegate, and
 manage the namespace.  Violation of those assumptions could impact
 the utility of the NBN URN namespace.
 URN:NBNs are in production use in several European countries
 including (in alphabetical order) Austria, Finland, Germany, Hungary,
 Italy, the Netherlands, Norway, Sweden, and Switzerland.  The URN:NBN
 namespace is collectively managed by these national libraries.  URN:
 NBNs have been applied to diverse content including Web archives,
 digitized materials, research data, and doctoral dissertations.  They
 can be used by national libraries and organizations cooperating with
 them.
 As a part of the initial development of the URN system in the late
 1990s, the IETF URN Working Group agreed that it was important to
 demonstrate that the URN syntax can accommodate existing identifier
 systems.  RFC 2288 [RFC2288] investigated the feasibility of using
 ISBN, ISSN, and SICI (Serial Item and Contribution Identifier) as
 URNs, with positive results; however, it did not formally register
 corresponding URN namespaces.  (For further discussion of how these
 systems have evolved as URNs, see RFC 8254 [RFC8254].)  This was in
 part due to the still-evolving process to formalize criteria for
 namespace definition documents and registration.  The criteria were
 consolidated later in the IETF, first in RFC 2611 [RFC2611], then RFC
 3406 [RFC3406], and now RFC 8141 [RFC8141].
 URN namespaces have been registered for NBN, ISBN, and ISSN in RFCs
 3188 [RFC3188], 3187 [RFC3187], and 3044 [RFC3044], respectively.
 ISBN and ISSN namespaces were made compliant with RFC 8141 [RFC8141]
 in 2017 by publishing revised ISSN [ISSN-namespace] and ISBN
 [ISBN-namespace] namespace registrations.

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 The term "National Bibliography Number" encompasses persistent local
 identifier systems that national libraries and their partner
 organizations use in addition to the more formally (and
 internationally) established identifiers.  These partner
 organizations include universities and their libraries and other
 subsidiaries, other research institutions, plus governmental and
 public organizations.  Some national libraries maintain a significant
 number of these liaison relationships; for instance, the German
 National Library had almost 400 by early 2018 [NBN-Resolving].
 In practice, NBN differs from standard identifier systems such as
 ISBN and ISSN because it is not a single identifier system with
 standard-specified scope and syntax.  Each NBN implementer creates
 its own system with its own syntax and assignment rules.  Each user
 organization is also obliged to keep track of how NBNs are being
 used; however, within the generic framework set in this document,
 local NBN assignment policies may vary considerably.
 Historically, NBNs have been applied in the national bibliographies
 to identify the resources catalogued into them.  Prior to the
 emergence of bibliographic standard identifiers in the early 1970s,
 national libraries assigned NBNs to all catalogued publications.
 Since the late 1990s, the NBN scope has been extended to cover a vast
 range of resources, both originally digital and digitized.  Only a
 small subset of these resources is catalogued in the national
 bibliographies or other bibliographic databases.  Digitized resources
 and their component parts (such as still images in books or journal
 articles) are examples of resources that may get NBNs.
 It is possible to extend the scope of the NBN much further.  The
 National Library of Finland is using them in the Finnish National
 Ontology Service Finto to identify corporate names (see
 <http://finto.fi/cn/en/>).  Using NBNs to identify metadata elements
 provides a stable basis for creation of linked data.
 Simple guidelines for using NBNs as URNs and the original namespace
 registration were published in RFC 3188 [RFC3188].  The RFC at hand
 replaces RFC 3188; sections discussing the methods by which URN:NBNs
 should be resolved have been updated, unused features have been
 eliminated, and the text is compliant with the stipulations of the
 revised URN specification [RFC8141].

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2. Conventions Used in This Document

 "NBN" refers to any National Bibliography Number identifier system
 used by the national libraries (or equivalent organizations) and
 other institutions, which use these identifiers with national
 libraries' support and permission.
 In this memo, "URN:NBN" is used as a shorthand for "NBN-based URN".
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

3. Fundamental Namespace and Community Considerations for NBN

3.1. The URN:NBN Namespace

 NBNs are widely used to identify both hand-held and digital resources
 in the collections of national libraries and other institutions that
 are responsible for preserving the cultural heritage of their
 constituents.  Resources in these collections are usually preserved
 for a long time (i.e., for centuries).  While the preferred methods
 for digital preservation may vary over time and depend on the
 content, the favorite one has been migration.  Whenever necessary, a
 resource in an outdated file format is migrated into a more modern
 file format.  To the extent possible, all old versions of the
 resource are also kept in order to alleviate the negative effects of
 partially successful migrations and the gradual loss of original look
 and feel that may accompany even fully successful migrations.  When
 NBN is used to identify manifestations and there are many of them for
 a single work, local policy can require that each manifestation ought
 to have its own NBN.
 NBNs are typically used to identify objects for which standard
 identifiers such as ISBN are not applicable.  However, NBNs can be
 used for component resources even when the resource as a whole
 qualifies for a standard identifier.  For instance, if a digitized
 book has an ISBN, JPEG image files of its pages might be assigned
 NBNs.  These URN:NBNs can be used as persistent links to the pages.
 The scope of standard identifier systems such as ISBN and ISSN is
 limited; they are applicable only to certain kinds of resources.  One
 of the roles of the NBN is to fill in the gaps left by the standard
 identifiers.  Collectively, these identifiers and NBNs cover all
 resources that national libraries and their partners need to include
 in their collections.

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 Section 4 below, and particularly Section 4.1, present a more
 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.  As coordinators of NBN usage, national libraries have
 allowed other organizations, such as university libraries or
 governmental organizations, to assign NBNs to the resources these
 organizations preserve for the long term.  In such case, the national
 library coordinates the use of NBNs at the national level.  National
 libraries can also provide URN resolution services and technical
 services to other NBN users.  These organizations are expected to
 either establish their own URN resolution services or use the
 technical infrastructure provided by the national library.  URN:NBNs
 are expected to be resolvable and support one or more resolution
 services.
 Although NBNs can be used to identify component resources, the NBN
 namespace does not specify a generic, intrinsic syntax for doing
 that.  However, there are at least two different ways in which
 component resources can be taken into account within the NBN
 namespace.
 The simplest and probably the most common approach is to assign a
 separate NBN for each component resource, such as a file containing a
 digitized page of a book, and make no provisions to make such NBNs
 discernible in a systematic way from others.
 Second, if the stipulations of the URI generic syntax [RFC3986] and
 the Internet media type specification [RFC2046] are met, in
 accordance with the provisions in RFC 8141 [RFC8141], the URN
 f-component can be attached to URN:NBNs in order to indicate the
 desired location within the resource supplied by URN resolution.
 From the library community point of view, it is important that the
 f-component is not a part of the Namespace-Specific String (NSS), and
 therefore f-component attachment does not mean that the relevant
 component part is identified.  Moreover, the resolution process still
 retrieves the entire resource even if there is an f-component.  The
 component part selection is applied by the resolution client (e.g.,
 browser) to the resource returned by the resolution process.  In
 other words, in this latter case the component parts are just logical
 and physical parts of the identified resource whereas in the former
 cases they are independently named entities.

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 Resources identified by NBNs are not always available in the
 Internet.  If one is not, the URN:NBN can resolve to a surrogate such
 as a metadata record describing the identified resource.
 Section 4 below, and particularly Section 4.4, presents a detailed
 overview of the application of the URN:NBN namespace as well as the
 principles of, and systems used for, the resolution of NBN-based
 URNs.

4. National Bibliography Number URNs

4.1. Assignment

 National Bibliography Number (NBN) is a generic term referring to a
 group of identifier systems administered by national libraries and
 institutions authorized by them.  The NBN assignment is typically
 performed by the organization hosting the resource.  National
 libraries are committed to permanent preservation of their deposit
 collections.
 Assignment of NBN-based URNs is controlled on a national level by the
 national library (or national libraries, if there is more than one).
 National guidelines can differ, but the identified resources
 themselves are usually persistent.
 Different national URN:NBN assignment policies have resulted in
 varying levels of control of the assignment process.  Manual URN:NBN
 assignment by the library personnel provides the tightest control,
 especially if the URN:NBNs cover only resources catalogued into the
 national bibliography.  In most national libraries, the scope of
 URN:NBN is already much broader than this.  Usage rules can vary
 within one country, from one URN:NBN sub-namespace to the next.
 Each national library uses NBNs independently of other national
 libraries; apart from this document, there are no guidelines that
 specify or control NBN usage.  As such, NBNs are unique only on the
 national level.  When used as URNs, base NBN strings MUST be
 augmented with a controlled prefix, which is the particular nation's
 ISO 3166-1 alpha-2 two-letter country code (referred to as "ISO
 country code" below) [ISO3166-1].  These prefixes guarantee
 uniqueness of the URN:NBNs at the global scale [ISO3166MA].
 National libraries using URN:NBNs usually specify local assignment
 policies for themselves.  Such policy can limit the URN:NBN usage to,
 e.g., the resources stored in the national library's digital
 collections or databases.  Although this specification does not

Hakala Informational [Page 7] RFC 8458 NBN URNs October 2018

 specify principles for URN:NBN assignment policies that can be
 applied, NBNs assigned to short-lived resources should not be made
 URN:NBNs unless such policy can be justified.
 URN:NBN assignment policy can clarify, for instance, the local policy
 concerning identifier assignment to component parts of resources and
 can specify, with sufficient detail, the syntax of local component
 identifiers (if there is one as a discernible part of the NBNs).  The
 policy can also cover any employed extensions to the default NBN
 scope.
 NBNs as such are locally but not globally unique; two national
 libraries can assign the same NBN to different resources.  A prefix,
 based on the ISO country code as described above, guarantees the
 global uniqueness of URN:NBNs.  Once an NBN has been assigned to a
 resource, it MUST be persistent, and therefore URN:NBNs are
 persistent as well.
 A URN:NBN, once it has been generated from a NBN, MUST NOT be reused
 for another resource.
 Users of the URN:NBN namespace MUST ensure that they do not assign
 the same URN:NBN twice.  Different policies can be applied to
 guarantee this.  For instance, NBNs and corresponding URN:NBNs can be
 assigned sequentially by programs in order to avoid human mistakes.
 It is also possible to use printable representations of checksums
 such as SHA-1 [RFC6234] as NBNs.

4.2. Syntax

 The Namespace-Specific String (NSS) will consist of three parts:
 o  a prefix consisting of an ISO 3166-1 alpha-2 country code and
    optional sub-namespace code(s) separated by a colon(s);
 o  a hyphen (-) as the delimiting character; and,
 o  an NBN string assigned by the national library or sub-delegated
    authority.

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 The following formal definition uses ABNF [RFC5234].
  nbn-nss     = prefix "-" nbn-string
  prefix      = iso-cc *( ":" subspc )
              ; The entire prefix is case insensitive.
  iso-cc      = 2ALPHA
              ; Alpha-2 country code as assigned by part 1 of ISO 3166
              ; (identifies the national library to which the branch
              ; is delegated).
  subspc      = 1*(ALPHA / DIGIT)
              ; As assigned by the respective national library.
  nbn-string  = path-rootless
              ; The "path-rootless" rule is defined in RFC 3986.
              ; Syntax requirements specified in RFC 8141 MUST be
              ; taken into account.
 A colon SHOULD be used within the prefix only as a delimiting
 character between the ISO 3166-1 country code and sub-namespace
 code(s), which splits the national namespace into smaller parts.
 The structure (if any) of the nbn_string is determined by the
 authority for the prefix.  Whereas the prefix is regarded as case
 insensitive, NBN strings can be case sensitive at the preference of
 the assigning authority; parsers therefore MUST treat these as case
 sensitive, and any case mapping needed to introduce case
 insensitivity is the responsibility of the relevant resolution
 system.
 A hyphen SHOULD be used as the delimiting character between the
 prefix and the NBN string.  Within the NBN string, a hyphen MAY be
 used for separating different sections of the identifier from one
 another.
 All two-letter codes are reserved by the ISO 3166 Maintenance Agency
 for either existing or possible future ISO country codes (or for
 private use).
 Sub-namespace identifiers MUST be registered on the national level by
 the national library that assigned the identifier.  The list of such
 identifiers can be made publicly available via the Web.
 Note that because case mapping for ASCII letters is completely
 reversible and does not lose information, the case used in case-
 insensitive matching is a local matter.  Implementations can convert

Hakala Informational [Page 9] RFC 8458 NBN URNs October 2018

 to lower or upper case as they see fit; they only need to do it
 consistently.

4.2.1. Usage of r-component and q-component

 URN:NBN resolvers do not currently support the use of either
 r-component or q-component.
 Resolution services based on r-component can be implemented in the
 future when the r-component syntax and semantics have been specified.

4.2.2. Usage of f-component

 If URN:NBN resolves to the identified resource and the media type of
 the resource supports f-component usage, it can be used to indicate a
 location within the identified resource.  Persistence is achieved if
 the URN:NBN is assigned to one and only one version of a resource,
 such as a PDF/A version of a book.
 The URN:NBN namespace does not impose any restrictions of its own on
 f-component usage.

4.3. Encoding Considerations and Lexical Equivalence

 Expressing NBNs as URNs is usually straightforward, as normally only
 ASCII characters are used in NBN strings.  If this is not the case,
 non-ASCII characters in NBNs MUST be translated into canonical form
 as specified in RFC 8141.  If a national library uses NBNs that can
 contain percent-encoded characters higher than U+007F, the library
 needs to carefully define the canonical transformation from these
 NBNs into URNs, including normalization forms.
 When an NBN is used as a URN, the NSS MUST consist of three parts:
 o  a prefix, structured as a primary prefix, which is a two-letter
    ISO 3166-1 country code of the library's country, and zero or more
    secondary prefixes that are each indicated by a delimiting colon
    character (:) and a sub-namespace identifier;
 o  a hyphen (-) as a delimiting character; and,
 o  the NBN string.
 Different delimiting characters are not semantically equivalent.
 The syntax and roles of the three parts listed above are described in
 Section 4.2.

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 If there are several national libraries in one country, these
 libraries MUST agree on how to divide the national namespace between
 themselves using this method before the URN:NBN assignment begins in
 any of these libraries.
 A national library MAY also assign URN:NBN sub-namespaces to trusted
 organizations such as universities or government institutions.  The
 sub-namespace MAY be further divided by the partner organization.
 All sub-namespace identifiers used within 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.
 Being part of the prefix, sub-namespace identifier strings are case-
 insensitive.  They MUST NOT contain any colons or hyphens.
 Formally, two URN:NBNs are lexically equivalent if they are octet-
 by-octet equal after the following (conceptional) preprocessing:
 1.  convert all characters in the leading "urn:nbn:" token to a
     single case;
 2.  convert all characters in the prefix (country code and its
     optional sub-divisions) to a single case; and,
 3.  convert all characters embedded in any percent-encodings to a
     single case.
 Models (indicated line break 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>
 Examples:
    URN:NBN:fi-fe201003181510
    urn:nbn:ch:bel-9039
    urn:nbn:se:uu:diva-3475
    urn:nbn:hu-3006

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4.4. Resolution and Persistence of NBN-based URNs

 Eventually, URNs might be resolved with the help of a Global Resolver
 Discovery Service (GRDS), and URN:NBN syntax makes it possible to
 locate the relevant resolver.  Since no GRDS system has been
 installed yet in the Internet, URN:NBNs are 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.  For instance, in Finland, the address of the national URN
 resolver is <http://urn.fi>.  Thus, the HTTP URI for the Finnish URN
 in the example above is <http://urn.fi/URN:NBN:fi-fe201003181510>.
 The country-code-based prefix part of the URN:NBN namespace-specific
 string will provide a hint needed to find the correct resolution
 service for URN:NBNs from the GRDS when it is established.
 There are three interrelated aspects of persistence that need to be
 discussed: persistence of the objects itself, persistence of the
 identifier, and persistence of the URN resolvers.
 NBNs have traditionally been assigned to printed resources, which
 tend to be persistent.  In contrast, digital resources require
 frequent migrations to guarantee accessibility.  Although it is
 impossible to estimate how often migrations are needed, hardware and
 software upgrades take place frequently, and a lifetime exceeding
 10-20 years can be considered as long.
 However, it is a common practice to keep also the original and
 previously migrated versions of resources.  Therefore, even outdated
 versions of resources can be available in digital archives, no matter
 how old or difficult to use they have become.
 If all versions of a resource are kept, a user who requires
 authenticity can retrieve the original version of the resource,
 whereas a user to whom the ease of use is a priority is likely to be
 satisfied with the latest version.  In order to enable the users to
 find the best match, a national library can link all manifestations
 of a resource to each other so as to make a user aware of them.
 Thus, even if specific versions of digital resources are not normally
 persistent, persistent identifiers such as URN:NBNs support
 information architectures that enable persistent access to any
 version of the resource, including ones that can only be utilized by
 using digital archaeology tools such as custom-made applications to
 render the resource.

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 Persistence of URN resolvers themselves is mainly an organizational
 issue that is related to the persistence of organizations maintaining
 them.  As URN:NBN resolution services will be supplied (primarily) by
 the national libraries, these services are likely to be long lived.

4.5. Additional Considerations

 It is a good idea to apply URN:NBNs (or other persistent identifiers)
 to all resources that have been prioritized in the organization's
 digital preservation plan.
 Assignment of URN:NBNs to resources that are known to not be
 persistent should be considered carefully.  URN:NBNs can, however, be
 applied to resources that have a low-level preservation priority and
 will not be migrated to more modern file formats or preserved via
 emulation.
 If the identified version of a resource has disappeared, the
 resolution process can supply a surrogate if one exists.  A surrogate
 can be, for instance, a more modern digital version of the original
 electronic resource.

5. URN Namespace ID (NID) Registration for the National Bibliography

  Number (NBN)
 This URN namespace registration describes how National Bibliography
 Numbers (NBNs) can be supported within the URN framework; it uses the
 updated IANA template specified in RFC 8141.
 Namespace Identifier:  NBN
    This namespace ID was formally assigned to the National
    Bibliography Number in October 2001, when the namespace was
    registered officially [RFC3188].  Utilization of URN:NBNs had
    started in demo systems already in 1998.  Since 2001, tens of
    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 many national libraries using the system
    have formed new liaisons.
 Version:  4
 Date:  2018-04-09

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 Registrant:
    Name: Juha Hakala
    Affiliation: Senior Adviser, The National Library of Finland
    Email: juha.hakala@helsinki.fi
    Postal: P.O. Box 15, 00014 Helsinki University, Finland
    Web URL: http://www.nationallibrary.fi/
    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).  The NBN
    namespace is available for free for the national libraries.  They
    can allow other organizations to assign URN:NBNs and use the
    resolution services established by the library for free or for a
    fee.  The fees, if collected, can be based on, e.g., the
    maintenance costs of the system.
 Purpose:  See Section 3 of RFC 8458
 Syntax:  See Section 4.2 of RFC 8458
 Assignment:  See Section 4.1 of RFC 8458
 Security and Privacy:  See Section 7 of RFC 8458
 Interoperability:
    National libraries and their partners usually apply URN:NBNs if a
    standard identifier such as ISBN is not applicable for the
    resource to be identified.  Some overlap with other URN namespaces
    is possible.
    URN:NBNs may contain characters which must be percent-encoded, but
    usually they consist of printable ASCII characters only.
 Resolution:  See Section 4.4 of RFC 8458
 Documentation:  RFC 8458
 Revision Information:
    This version of the URN:NBN namespace registration has been
    updated to use the revised definition of URN syntax from RFC 8141,
    although usage of r-components is not specified yet.  In addition,
    non-ISO 3166 (country code) based NBNs have been deleted due to
    lack of deployment.  The entire NBN prefix is now specified to be
    case insensitive in accordance with established practice.  This
    version also includes numerous clarifications based on actual
    usage of URN:NBNs.

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6. IANA Considerations

 IANA has updated the existing registration of the formal URN
 namespace, "NBN", using the template given above in Section 5.

7. Security Considerations

 This document defines means of encoding NBNs as URNs.  A URN
 resolution service for NBN-based URNs is depicted but only at a
 generic level; thus, questions of secure or authenticated resolution
 mechanisms and authentication of users are out of scope of this
 document.
 Although no validation mechanisms are specified on the global level
 (beyond a routine check of those characters that require special
 encoding when employed in URIs), NBNs assigned by any given authority
 can have a well-specified and rich syntax (including, e.g., fixed
 length and checksum).  In such cases, it is possible to validate the
 correctness of NBNs programmatically.
 Issues regarding intellectual property rights associated with objects
 identified by the URN:NBNs are beyond the scope of this document, as
 are questions about rights to the databases that might be used to
 construct resolution services.
 Beyond the generic security considerations laid out in the underlying
 documents listed in the Normative References, no specific security
 threats have been identified for NBN-based URNs.

8. References

8.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66,
            RFC 3986, DOI 10.17487/RFC3986, January 2005,
            <https://www.rfc-editor.org/info/rfc3986>.
 [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234,
            DOI 10.17487/RFC5234, January 2008,
            <https://www.rfc-editor.org/info/rfc5234>.

Hakala Informational [Page 15] RFC 8458 NBN URNs October 2018

 [RFC8141]  Saint-Andre, P. and J. Klensin, "Uniform Resource Names
            (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
            <https://www.rfc-editor.org/info/rfc8141>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2. Informative References

 [IANA-URI] IANA, "Uniform Resource Identifier (URI) Schemes",
            <http://www.iana.org/assignments/uri-schemes>.
 [IANA-URN] IANA, "Uniform Resource Names (URN) Namespaces",
            <http://www.iana.org/assignments/urn-namespaces>.
 [ISBN-namespace]
            Griffiths, S., "Namespace Registration for International
            Standard Book Number (ISBN) ISO 2108:2017",
            <https://www.iana.org/assignments/urn-formal/isbn>.
 [ISO3166-1]
            ISO, "Codes for the representation of names of countries
            and their subdivisions -- Part 1: Country codes",
            ISO 3166-1:2013, November 2013,
            <https://www.iso.org/standard/63545.html>.
 [ISO3166MA]
            ISO, "ISO 3166 Country Codes",
            <https://www.iso.org/iso/country_codes.htm>.
 [ISSN-namespace]
            Bequet, G., "Namespace Registration for International
            Standard Serial Number (ISSN) and Linking ISSN (ISSN-L)
            based on ISO 3297:2007", June 2017,
            <https://www.iana.org/assignments/urn-formal/issn>.
 [NBN-Resolving]
            Deutsche Nationalbibliothek, "URN:NBN Resolver fuer
            Deutschland und Schweiz: Information ueber Partner
            Institutionen", <https://nbn-resolving.org/institutions>.
 [PERSID]   PersID initiative, 2009-2011, "persid: Building a
            persistent identifier infrastructure",
            <http://www.persid.org>.

Hakala Informational [Page 16] RFC 8458 NBN URNs October 2018

 [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Two: Media Types", RFC 2046,
            DOI 10.17487/RFC2046, November 1996,
            <https://www.rfc-editor.org/info/rfc2046>.
 [RFC2141]  Moats, R., "URN Syntax", RFC 2141, DOI 10.17487/RFC2141,
            May 1997, <https://www.rfc-editor.org/info/rfc2141>.
 [RFC2288]  Lynch, C., Preston, C., and R. Daniel, "Using Existing
            Bibliographic Identifiers as Uniform Resource Names",
            RFC 2288, DOI 10.17487/RFC2288, February 1998,
            <https://www.rfc-editor.org/info/rfc2288>.
 [RFC2611]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
            "URN Namespace Definition Mechanisms", BCP 33, RFC 2611,
            DOI 10.17487/RFC2611, June 1999,
            <https://www.rfc-editor.org/info/rfc2611>.
 [RFC3044]  Rozenfeld, S., "Using The ISSN (International Serial
            Standard Number) as URN (Uniform Resource Names) within an
            ISSN-URN Namespace", RFC 3044, DOI 10.17487/RFC3044,
            January 2001, <https://www.rfc-editor.org/info/rfc3044>.
 [RFC3187]  Hakala, J. and H. Walravens, "Using International Standard
            Book Numbers as Uniform Resource Names", RFC 3187,
            DOI 10.17487/RFC3187, October 2001,
            <https://www.rfc-editor.org/info/rfc3187>.
 [RFC3188]  Hakala, J., "Using National Bibliography Numbers as
            Uniform Resource Names", RFC 3188, DOI 10.17487/RFC3188,
            October 2001, <https://www.rfc-editor.org/info/rfc3188>.
 [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
            "Uniform Resource Names (URN) Namespace Definition
            Mechanisms", RFC 3406, DOI 10.17487/RFC3406, October 2002,
            <https://www.rfc-editor.org/info/rfc3406>.
 [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
            (SHA and SHA-based HMAC and HKDF)", RFC 6234,
            DOI 10.17487/RFC6234, May 2011,
            <https://www.rfc-editor.org/info/rfc6234>.
 [RFC8254]  Klensin, J. and J. Hakala, "Uniform Resource Name (URN)
            Namespace Registration Transition", RFC 8254,
            DOI 10.17487/RFC8254, October 2017,
            <https://www.rfc-editor.org/info/rfc8254>.

Hakala Informational [Page 17] RFC 8458 NBN URNs October 2018

Appendix A. Significant Changes from RFC 3188

 Numerous clarifications have been made based on a decade of
 experience with RFC 3188.
 NBNs that are not based on ISO 3166 (country codes) have been removed
 due to lack of usage.
 In accordance with established practice, the whole NBN prefix is now
 declared case insensitive.
 The document is based on the new URN syntax specification, RFC 8141.
 Use of query components and fragment components with this namespace
 is now specified in accordance with RFC 8141.

Acknowledgements

 Revision of RFC 3188 started during the project PersID [PERSID].
 Later, the revision was included in the charter of the URNbis Working
 Group and worked on in that group in parallel with what became RFCs
 8141 and 8254.  The author wishes to thank his colleagues in the
 PersID project and the URNbis participants for their support and
 review comments.
 Tommi Jauhiainen has provided feedback on an early draft version of
 this document.  The author wishes to thank Tommi Jauhiainen, Bengt
 Neiss, and Lars Svensson for the comments they have provided to
 various draft versions of this document.
 John Klensin provided significant editorial and advisory support for
 later draft versions of the document.

Contributors

 This document would not have been possible without contributions by
 Alfred Hoenes.

Author's Address

 Juha Hakala
 The National Library of Finland
 P.O. Box 26
 FIN-00014 Helsinki University
 Finland
 Email: juha.hakala@helsinki.fi

Hakala Informational [Page 18]

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