EPICUR: Uniform Resource Name (URN) - Strategy of the German National Library

Please cite this document as: urn:nbn:de:1111-200606309

Stable references to digital objects, for example in information systems such as online catalogues or bibliographies can only be created if a standardised, persistent addressing system is used, such as the Uniform Resource Names (URNs) system. However the permanence of such an addressing system cannot be assured if it is only being applied locally. Within the context of the EPICUR project, the German National Library is pursuing the goal of creating the foundations for co-operative, usable conventions for managing and resolving URNs, so that the benefits of URNs as a standard can be consistently applied, for example as reliable references within online publications, search criteria or access mechanisms. In addition, quality criteria will be specified for the application of URNs from the namespace "nbn:de" ("National Bibliography Number" for Germany). The URN strategy described below will be primarily targeted to institutions such as library consortia, publishers, information providers and universty libraries who wish to assign and use URNs. At the same time it is also intended to provide an information basis for a more general circle of users.

1. What is the objective of the URN Strategy?

The German National Library provides the basic organisational and technical conditions to assign, manage and resolve URNs to all users of URNs in the namespace "nbn:de". URNs guarantee permanent access to the object in question. This access is guaranteed by means of high technical availability of the URN service and by means of stable object archiving. URNs will be referenced in national and international reference systems such as bibliographies, catalogues and search engines and can be transported across bibliographic exchange formats. The URN activities of the German National Library are tied in with international initiatives, projects and committees such as the CDNL "Persistent Identifiers" Working Group and the CENL Working Group on Networking Standards and is based on national, co-operatively agreed procedures in conjunction with library associations.

2. To what can a URN be assigned and managed?

2.1 Definition of a "digital URN object"

Within the context of URN management, the term "digital object" is understood as any single unit to which a URN can be assigned. A unit currently refers to a static publication, such as, for example, monographic online resources. A solution for dynamic, serial publications, in particular for periodicals, is still to be developed. Starting points for this already exist. The smallest unit of a digital object can be addressed by a generally used Internet access mechanism such as a URL.

2.2 Granularity of objects

A URN provides a reference to at least one of an entire object's URLs, by means of which an object is addressed. A URN can also refer to several copies of the same object, accessible through multiple URLs, and can incorporate a variety of object presentation formats.

Graphic of a URN pointing to multiple URLs

URNs can be assigned to addressable part objects.

Graphic of URN pointing to part objects

2.3 URN objects

The following can be counted as objects for which URNs from the namespace "nbn:de" can be assigned:

3. How will URNs (nbn:de) be allocated and managed?

URNs comprise several hierarchically constructed components. Amongst these are the namespace such as "nbn", which can however comprise several subordinate sub-namespaces such as "de". For the "nbn" namespace element, for which the German National Library has responsibility, the hierarchical structure which has been initiated at an international level will be continued at a national level.

3.1 Assigning URN (nbn:de) sub-namespaces

Assigning URN sub-namespaces is carried out centrally by the German National Library. Within these sub-namespaces URNs can be individually assigned in line with current requirements, though these must comply with the guidelines for structuring a URN.

3.2 Allocating a complete URN

Libraries belonging to library association structure URNs in line with the following approach

urn:nbn:de:[designations of library association]*:[official notation of university libraries]-[unique production number][check digit]

An example:


Institutions from within the area of responsibility of the BSZ use the abbreviation "bsz", NOT "swb" to identify the URN sub-namespace of this library association.

Institutions which are not organised as library association, such as publishers, or, in the case of co-operatively allocated NBNs, institutions which are not based in Germany, can apply to the German National Library to have their own sub-namespace. This will be structured as a four digit number.

urn:nbn:de:[four digit number]-[unique production number][check digit]

An example:


3.3 URN registration

URNs allocated in this decentralised way, as well as their associated URLs, are to be registered directly with the German National Library within 24 hours of their publication on a document server. This however affects only information relevant to the URN. Regular reporting of metadata to the German National Library is excluded from this. The 24 hour deadline must also be observed if the initial URN registration takes place via a third party, such as a regional aggregator.

3.4 The German National Library services

The German National Library provides the following services as part of its URN management:

Each institution with responsibility for a sub-namespace sets out a guideline of its services. These are published by the German National Library on its web presentation under http://www.persistent-identifier.de/. This includes

4. What principles and recommendations does URN management entail?

4.1 Principles for assigning URNs in the "nbn:de" namespace

4.2 Recommendations

Assigning URNs

Linking URNs with metadata

4.3 Recommendations for structuring URLs

A character set according to RFC 1738 for URLs should be used, so that URLs can be checked with some certainty by a linkcheck procedure. Special characters such as spaces and the German umlauts accent would have to be encoded as hexadecimals presentation or if possible avoided altogether.

*RFC 2396 Uniform Resource Identifier: Generic Syntax; RFC 1738 Uniform Resource Locators

5. What standard interfaces are available for the technical implementation of URN management?

Minimum standard

OAI 2.0 provide a simple, standardised interface in order to implement the EPICUR XML Schema that enables the complex URN management.


Near real-time processing of URN/URL data. An interface will be made available by the German National Library.

6. What resolution services are available?

The primary function of the resolver is to redirect a URN query to the location where the item is currently stored.

6.1 Standard resolver processes

If only one URL is registered together with a URN, then the resolver will point to this URL. If multiple URLs are managed by one URN, then a standard resolver procedure exists to return the URL with the highest priority. This for example be the URL for a full text document in a specific format such as PDF, or it could be a front door or front page URL, i.e. an internet document containing a meta-description of the object. In case this URL is temporarily or permanently not available, then a reference will automatically be provided to the URL with the next highest priority. The URL with the highest priority can be defined by an institution having responsibility for a sub-namespace and applies to the entire sub-namespace.

An example:

Standard request*:

GET http://nbn-resolving.de/urn/resolver.pl?urn=urn:nbn:de:gbv:089-3321752945

without parameters

Standard response:

Content of GET-Request http://edok01.tib.uni-hannover.de/edoks/e01dh01/332175294.pdf

6.2 Configurable resolver response behaviour

If several URLs are being administered to one URN, then individual URLs can be called up in a targeted way by the resolver, i.e. the user can influence the resolver's response behaviour.

An example:

Graphic: Configurable resolver response behaviour

Standardisation is the goal of this service specification in the form of an RFC.

In the EPICUR project, the following functions are planned for controlling the response behaviour of the URN resolver in responding to a URN request:

7. Does the German National Library administer URNs from external namespaces?

As a technical service, interested institutions will be offered URN management for external namespaces (other than "nbn:de). The aim of these individual URN applications will be determined by the institution responsible for the namespace in question. the German National Library will offer the following services: