A Digital Object Identification System

Introduction
A Digital Object Identifier (DOI) is a unique name (not a location) for an entity on digital networks and it provides a system for identification and exchange of this information (International DOI Foundation (IDF), 2004).

DOIs assigned in one context may be re-used in another place (or time) without consulting the assigner. As the services provided by DOI’s are outside the direct control of the assigner, they must be designed to be interoperable, persistent and extensible. For example, in a web context a DOI may be used in an http form as a URL (through a proxy server). Hence a DOI is designed as a generic framework applicable to any digital object, providing a structured, extensible means of identification, description and resolution.

The DOI system was built using several existing standards-based components, which have been brought together and further developed by the International DOI Foundation (IDF). The IDF is a cross-industry, cross-sector, not-for-profit organisation, which was founded in 1998. Membership in the IDF is open to all organizations with an interest in electronic publishing and related enabling technologies.

The DOI has recently been accepted for standardisation (ISO TC46/SC9) and is currently in widespread use for scientific publishing and in government documents. New applications, which demonstrate more added value and enhanced functionality, are generating strong interest from the music recording and other related publishing industries (many of which have led the way in developing it).

DOI System Components
The DOI system is made up of the following components:

• A specified standard numbering syntax;


• A resolution service (based on an existing Handle System);


• A data model incorporating a data dictionary (based on the indecs Data Dictionary); and


• An implementation mechanism of policies and procedures for the governance and application of DOIs.

DOI Syntax
The DOI syntax is a standard for constructing an opaque string with naming authority and delegation (NISO Z39.84, DOI Syntax) and provides a "container" which can accommodate any existing identifier. For example:

10.1234/NP5678
10.5678/ISBN-0-7645-4889-4 and
10.2224/2004-10-ISO-DOI
are all valid DOI syntax.

The DOI has two components, the prefix and the suffix, which together form the DOI. The portion following the "/" character (the DOI Suffix) may be an existing identifier (e.g., an ISBN or bar code). The portion preceding the "/" character (the DOI Prefix) denotes a unique naming authority that is assigned to an organization that wishes to register DOIs. This combination of a unique prefix and suffix avoids the need for the centralised allocation of DOI numbers.

DOI Resolution
Resolution is the process in which a DOI request is input to a network service to provide a specific output of one or more pieces of current information related to the identified entity (such as a ULR where the object can be found). Resolution provides a level of managed indirection between an identifier and the output and can be summarised as shown in the following diagram (International DOI Foundation (IDF), 2005).

http://www.doi.org/doi_presentations/resolution/doi_resolution_feb05.jpg

DOI Data Model
The DOI data model consists of a data dictionary and a framework for applying it. Together these provide tools for defining what a DOI specifies (through use of a data dictionary), and how DOIs relate to each other, (through a grouping mechanism, Application Profiles, which associate DOIs with defined common properties). This provides semantic interoperability, enabling information that originates in one context to be used in another in ways that are as highly automated as possible.

The DOI system uses an interoperable data dictionary, which contains terms from different computerized systems and shows the relationships they have with one another in a formal way. The purpose of an interoperable data dictionary is to support the use together of terms from different systems. The IDF is the Registration Authority (RA) for one such dictionary, the ISO/IEC MPEG-21 Rights Data Dictionary, and is the co-developer of a wider indecs Data Dictionary that includes this and is used by DOIs.

DOI Implementation
DOI is implemented through the IDF, which governs and safeguards (owns or licences on behalf of registrants) all intellectual property rights relating to the DOI System. It works with Registration Authorities to ensure that any improvements made to the DOI system (including creation, maintenance, registration, resolution and policymaking of DOIs) are available to any DOI registrant, and that no third party licenses might reasonably be required to practice the DOI standard (or the resolution of a DOI).

The IDF is not a standards body, but a central authority and maintenance agency. The IDF is the appointed Registration Authority (RA) for the ISO/IEC MPEG 21 Rights Data Dictionary, and is the proposed RA for the DOI System within ISO TC46/SC9. The IDF licenses authority to use the system through Registration Agencies, each of which can develop its own applications and use DOI in ways appropriate for their community and/or industry.

Links to Additional Information

http://www.doi.org/ Main DOI Web Page

http://www.doi.org/welcome.html International DOI Foundation

http://www.doi.org/about_the_doi.html Overview

http://www.doi.org/faq.html Frequently Asked Questions

http://www.doi.org/announce.html News and Events


Reference:
The International DOI Foundation (IDF). (n.d.). Introductory Overview: The Digital Object Identifier System. Updated 17 December, 2004, from
http://www.doi.org/overview/sys_overview_021601.html

The International DOI Foundation (IDF). (n.d.). Illustration showing DOI resolution process. (JPG). Updated 14 February 2005, from
http://www.doi.org/doi_presentations/resolution/doi_resolution_feb05.jpg