Examples of Persistent Identifiers

The Handle System

The Handle System is a technical development of the Corporation for National Research Initiatives (CNRI) for assigning, managing, and resolving PIs known as "handles". A set of protocols with reference implementations like e.g. DOI, LoC provides the technical basis. Please find additional information under CNRI.

The scheme below illustrates the structure of handles. They consist of a prefix and a suffix. The prefix is a numerical code indicating the institution. The suffix may be composed of any string of characters.

<Handle> ::= <Handle Naming Authority> "/" <Handle Local Name>

structure of handles

Digital Object Identifier (DOI)

Since 1998, applications of Digital Object Identifiers (DOI) have been coordinated by the International DOI Foundation (IDF). DOI is a system for identifying and exchanging any entity of intellectual property. At the same time, DOI provides technical and organisational general set-up to manage digital objects and connect producers or information providers with their customers. Thus, DOI derived services for electronic resources with limited access can be developed and automated.

The DOI system consists of three components:

If institutions intend to design a service with an individual profile, they can realise it via Registration Agencies. The most popular example is CrossRef, where metadata and storage locations of references of publications can be administered and processed by external institutions.

The DOI Foundation is a non-profit organisation compensating its costs through membership fees, sale of DOI prefixes and assigned DOI numbers.

Since 2001, the structure of DOIs has been standardised in the form of ANSI/NISO-standards (Z39.84) reflecting the handle components:

Prefix / Suffix

The numeric code "10" indicates strings as DOIs, the numerical order adjacent to the point "1045" represents the assigning institution e.g. a "Registration Agency". The alphanumeric string after the slash identifies the object e.g. a periodical article.


PURL (Persistent URL) was introduced in 1995 by the "Online Computer Library Center" (OCLC) in the framework of the "Internet Cataloguing Project" funded by the U.S. Department of Education in order to improve address presentation for cataloguing internet resources. PURLs are no Persistent Identifiers, yet can be transformed into existing standards like URNs. The existing internet standard "HTTP-redirect" is the technical basis to resolve PURLs into URLs.

Uniform Resource Name (URN)

Uniform Resource Name (URN) was created in 1992 as standard for addressing objects with the institutional commitment to serve as persistent, location-independent resource identifiers. URNs were designed to keep the cost for providing gateways and using URNs as low as possible - comparable to existing namespaces like e.g. URLs. Therefore, integration of existing or already applied namespaces or numeric systems into the URN scheme and common protocols like e.g. HTTP (Hypertext Transfer Protocol) or schemes like URLs was standardised.

URN standard is controlled by the Internet Engineering Task Force (IETF). It is responsible for developing and publishing standards in the form of "Request for Comments" (RFCs), including:

URNs consist of several hierarchically structured components like namespace (NID), composed of several subordinated subname spaces (SNID), and the namespace specific string (NISS).

The following example shows the common structure of a URN:


Within URNs, it is possible to integrate existing numeric systems (e.g. ISBN) and to establish institution-dependent numeric systems on national or international level as namespaces. This includes the "National Bibliography Number"(NBN, RFC 3188), an internationally managed namespace of national libraries with participation of the German National Library.