EPICUR - Uniform Resource Name (URN) - Strategy of the German National Library
EPICUR: Uniform Resource Name (URN) - Strategy of the German National Library
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.
URNs can be assigned to addressable part objects.
2.3 URN objects
The following can be counted as objects for which URNs from the namespace "nbn:de" can be assigned:
items currently archived by the German National Library. This includes:
- Online dissertations
- Online publications from publishers and other issuers.
items to be archived in the German National Library in the future. Network publications archived by the
German National Library to receive a URN (nbn:de), as well as any which, when archived, have a DOI or other
objects which will be administered on certified document servers
(e.g. endeavours by DINI),
with a perspective to making them permanently available via long term archiving.
In this case a workflow system would have to guarantee that URLs were updated. Workflow is here being used to mean
a firm arrangment between the German National Library and an institution with responsibility for a namespace. URL checks
are to be carried out centrally by the German National Library as part of the URN managment process and having there by
identified inactive URLs, institutions are then required to register new, valid URLs with the German National Library.
Further information on technical implementation can be found under Point 5 "
Which standard interfaces are available for technical implementation?".
A deadline of, for example, X working days has yet to be specified. Alternatively it is conceivable that a dedicated
interface for automatic registration at the German National Library may be implemented. The EPICUR project has already
taken this into account. The interface that meets these requirements will be implemented by the German National Library.
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]
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]
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:
- Interfaces for URN registration within 24 hours after publication on a document server.
- Periodic URL link check procedure
- Interfaces for updating URLs,
- Periodic authenticity checking of objects, initially based on MD5 fingerprints for objects up to 50MB.
Publishing services regarding sub-namespace on the German National Library server
- Configurable URN resolution,
- Maintaining a stable technical infrastructure
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
Setting the standard resolution for URNs
Information on whether a URL points to one URL or to several,
Allocating URNs for
- complete or partial objects,
- new versions of an object
- Authenticity checking of objects
- Guaranteeing archiving or long-term archiving of objects by other institutions, such as, for example long-term archiving
at the German National Library.
4. What principles and recommendations does URN management entail?
4.1 Principles for assigning URNs in the "nbn:de" namespace
URNs can only be assigned for digital objects within one's own area of responsibility. This applies regardless
of how the object is technically published, for example by an external institution.
URNs only become valid once they and their associated URLs have been registered at the German National Library.
If the contents of objects can be shown to have changed, for example by a change in their MD5-fingerprint, then
a new URN must be assigned.
A URN can only be assigned once, with no duplication.
If a digital object for which a URN has already been assigned is administered as a copy at some other institution,
then the URN must be transferred too. If the metadata are not transferred, then the institution in question must
be made aware of the existence of the URN, for example by using the URN as a way of accessing the object.
Only one URN from the "nbn.de" namespace may be allocated for one publication.
Use of a check digit for checking URN numbering consistency is required for decentralised allocation of URNs and
centralised registration of URNs. A check digit algorithm is used
If a digital object is managed on a document server without also being archived, all registered URLs can become
permanently inactive. Such instances must be reported to the German National Library. A URN becomes invalid. The
resolver provides this information in response to a URN request. In such cases the URN may not be re-used
for any other publication.
URNs should be assigned as closely as possible to the object, i.e. they should point to the URL which refers directly to the object.
The set of characters used in the URN should be kept simple, in order to avoid complex conversions as a result of using special
characters. The possibility to remember a URN is enhanced through using a simple character set.
Linking URNs with metadata
URNs should be a component of metadata. This means that a URN should be integrated into the metadata of the object in question
during the URN assignment process.
In case the objects also covered by the legal collection mandate of the German National Library's, it would be desirable to make
dispositions that these metadata could be reported to the German National Library, or that the German National Library had the option
of acquiring these metadata via an appropriate interface.
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?
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.
Content of GET-Request
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.
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:
- All active URLs, encoded in HTML or XML, will be delivered via HTTP.
- A URL which refers to an object of a particular MimeType, e.g. PDF, can be searched for.
- URLs from a particular institution,
- from an archive server or
- from a document server (original URLs) can be specifically controlled.
- A reference to a newer version of a URL as well as
- the allocation of the URN for a part document to the URN of the complete document is possible.
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
Registration of relevant URN data as well as reporting changes will take place via the interface
provided by the German National Library for the "nbn.de" sub-namespace.
- the German National Library's services can be used for URN resolution.
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