Persistent Identifiers

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					                                                                      Persistent Identifiers

                                                           • URI (Uniform Resource Identifier). Provides
 Overview                                                    a standard, unique method for identifying a
 Persistent identifiers are a prerequisite for sustained     resource. It consists of a scheme name (http), a
 and reliable resource discovery. A number of                domain name ( and a path (/
 persistent identification systems have been                 example.htm). URLs (which specify a resource
 developed that use different technical approaches           location) and URNs (which specify the resource
 and operate at different levels. This briefing              name independent of location) are both forms of
 paper introduces some of the systems currently              URIs. Many persistent identification systems are
 available to support persistent identification of           based on or extend the URI framework.
 digital resources, and points to resources to help        • PURL (Persistent Uniform Resource Locator).
 deployment within institutional repositories.               Takes the concept of the URL and adds a
                                                             resolution service context. Instead of the URL
What are Persistent Identifiers?                             pointing directly to the resource in question, it
                                                             references an intermediate PURL resolution
The use of location-based identifiers such as
                                                             service. This service is used to look up the actual
the Uniform Resource Locator (URL) can lead to
                                                             address of the URL before redirecting to the
problems accessing resources over time. When
                                                             appropriate resource.
accessing a resource via a hyperlink users may
receive a “404 - page not found” error, which is           • Handle. Identifies the resource address by a
caused by the resource being moved, relocated or             unique handle assigned by a common registration
renamed while external links to the resource remain          service. When the browser receives a handle,
unchanged.                                                   it is sent to the global registration service for
                                                             resolution and redirection to a local handle server
Persistent identifiers attempt to solve the problems         which in turn can resolve the local part of the
of resource identification and long-term access to           identifier to the resource in the repository.
online digital materials. A persistent identifier allows   • DOI (Digital Object Identifier). Makes use of the
the resource to be uniquely identified in a way
                                                             Handle system as a resolution service but gives
that will not change if the resource is renamed or
                                                             additional services such as descriptive metadata
relocated, and will persist regardless of the protocol
                                                             about the digital object that is being represented.
used to access it. This means that a resource can
be reliably referenced for future access by humans           DOIs are mainly used by publishers to identify
and software.                                                journal articles, but have also been used by
                                                             repositories to identify documents or data.
An important part of persistence is organisational
policy, not just the adoption of technical solutions.
In essence, the persistence of an object is only
                                                           Using PIs with digital repositories
effective if the organisation maintains and manages        Persistent identifiers are widely used in digital
this persistence. In this manner even a URL could          repositories, providing valued-added services to
be considered persistent so long as it is maintained       a user: guaranteeing globally unique identifiers
by some administrative service.                            through a centrally-run registration service, a
                                                           persistent relationship between an identifier and
Different systems in use                                   the same resource over time, and reliable services
                                                           for managing and using these identifiers over time.
Examples of persistent identifiers in use include
                                                           Making use of this infrastructure will provide a
                                                           foundation for utilities such as:
and URN. Within the repository environment a
common subset of identifiers are often used, the
most relevant of which are:

   Briefing Paper                                                                            November 2008
Persistent Identifiers                                                          

• Access to resources over time. Identifier              How can a repository administrator make use
  infrastructure can support access to resources as      of a global identifier system? Most repository
  they are moved from one repository or data store       platforms have been designed for persistence,
  to another.                                            in many cases allowing implementation of these
• Discovery. Persistent identifiers provide the          services with minimal additional resource. This
  link between the discovery of resources from           might involve registering with a resolution service to
  federated repositories and access to those             receive an identifier. Once this identifier has been
  resources. The metadata returned from a                received, the repository software can be configured
  discovery service can contain an identifier that       appropriately by the system administrator. The types
  is resolved to the location of the resource at the     of identifiers vary across software platforms, so it is
  time of discovery.                                     advisable to seek information from the vendor of the
                                                         repository system and from the relevant technical
• Enhanced resource management. Identifiers
  can be used to model complex relationships
  between resources and make it possible to
  manage compound resources and distributed              Conclusion
  copies of a resource, to distinguish between           Persistent identification plays a key role in ensuring
  different versions of a resource, and to help          long-term access to objects within repositories, but
  decide which is the most appropriate copy or           it doesn’t happen automatically. Persistent access
  version for a user.                                    needs to be backed by institutional policy, and can
• Rights management. Identifiers can be used             be assisted by a number of technical solutions.
  to associate rights information with resources.        Remember, don’t lose your audience to 404 errors,
  They can also be used to track the relationship        by ensuring works in the repository have identifiers
  between a resource and derived works.                  that persist through time.

   References & further information:
   JISC Standards Catalogue
   Documented Identifier Standards include URI, OpenURL, Z39.88-2004, DOI, PURL, Handle, ARK, INFO
   and COinS

   PILIN Project
   Persistent Identifier Linking Infrastructure project, aimed to pave the way for a national persistent
   identifier service for Australia

   Preserving Access to Digital Information, on Persistent identifiers
   PADI, from the National Library of Australia, provides information on digital preservation

   Resource Identifier Interoperability for Repositories (RIDIR)
   The JISC RIDIR project investigated the requirements for the use of persistent identifiers to facilitate
   interoperability between digital repositories

   Tonkin, E., Persistent Identifiers: Considering the Options, Ariadne, issue 56, July 2008

   Repositories Support Project
   The Repositories Support Project (RSP) aims to deliver good practice and practical advice to HEIs to
   enable the implementation, management and development of digital institutional repositories

  Briefing Paper                                                                                November 2008