A digital object identifier
) is a permanent identifier given to an electronic document
. Similar to a Uniform Resource Name (URN)
, but in contrast to a Uniform Resource Locator (URL)
, it is not dependent upon the electronic document's location. The International DOI Foundation (IDF) defines DOI name
as "a digital identifier
for any object of intellectual property
"; it explains that the DOI is used for "persistently identifying a piece of intellectual property on a digital network and associating it with related current data in a structured extensible way. DOI
is a registered trademark
of the IDF. A typical use of a DOI is to give a scholarly paper or article a unique identifying number that anyone can use to obtain information about the publication's location on a digital network.
The DOI system is an implementation of the Corporation for National Research Initiatives's (CNRI) handle system, a system for assigning names to objects for name resolution. DOIs are handles with the prefix "10."; handles for other namespaces in the Handle System have different prefixes. DOIs can be resolved at The DOI System and at The Handle System
Comparison with other standards
A DOI differs from commonly used internet
pointers to material such as the URL
, because it identifies an object as a first-class
entity, not simply the place where the object is located. A DOI also differs from identifiers such as the International Standard Book Numbers (ISBN)
, International Standard Recording Codes (ISRC)
, etc. because it can be associated with defined services and is immediately actionable on a network.
A DOI can apply to any form of document expressed in any digital environment, including both physical and digital media manifestations, performances and abstract works. DOIs can be used to identify: e-texts; images; audio or video items and software, etc. An entity can be identified at any arbitrary level of granularity. This means that, for instance, DOIs can identify a journal, an individual issue of a journal, an individual article in the journal or a single table in that article.
The DOI consists of a unique alphanumeric
character string divided into two parts: a prefix
and a suffix
An example of a complete DOI is:
10.1000 is the prefix:
10 is the directory code. The directory code must be numeric; valid directory codes are determined by the maintenance agency (the International DOI Foundation). At present, the only valid directory code is 10 and all valid DOI's begin with "10.".
1000 is the registrant's code or publisher ID, identifying the registrant. In this case, the number identifies the International DOI Foundation.
182 is the suffix, or item ID, identifying the single object. (Typical suffixes are longer than this example.) In this case, the object corresponding to doi:10.1000/182 is the DOI Handbook, Version 4.4.1.
The prefix is assigned by a DOI Registration Agency to a specific registrant. The suffix is assigned by the registrant and must be unique within a prefix. It can integrate existing standard identifiers such as an ISBN or ISSN, or SICI. The DOI is case insensitive and is considered an "opaque string": nothing can be inferred from the number with respect to its use in the DOI System.
The correct way to cite a DOI on a webpage or in a publication is doi:10.1000/182
DOI resolution redirects the user from a DOI to one or more pieces of typed data: URLs representing instances of the object, services such as e-mail, or one or more items of metadata.
"What the DOI identifies" and "what the DOI resolves to" are two different concepts: it is possible that a DOI does not resolve to the identified entity, but just to some related information wished by the publisher.
DOI resolution is provided through the Handle System technology, developed by the Corporation for National Research Initiatives, and is freely available to any user encountering a DOI. To resolve a DOI, just type in the address bar of any web browser the string
followed by the DOI of the document.
For example, to resolve the DOI 10.1000/182, enter into your browser the address:
http://dx.doi.org/10.1000/182. Of course, web pages or other hypertext documents can include hypertext links in this form, as in this sentence which links to the DOI Handbook Some browsers allow the direct resolution of a DOI (or other handles) with an add-on.
There are several other ways to resolve a DOI, for example, one can use
http://hdl.handle.net/ followed by the DOI of the document.
The DOI organization has applied for a "doi:" URI scheme to allow a DOI to be expressed as a Uniform Resource Identifier (URI) without requiring reference to a specific HTTP server as in the previous paragraph. As of April 2006, this had not been approved.
Each DOI is associated with a series of metadata, a set of bibliographical and commercial information concerning the content (title, author, publication date, copyright, price, etc.) and its position within the whole registrant's publishing offer (the belonging of a title to a series, of an article to a serial, the availability of one publication in more formats and/or through different media, etc.). By means of metadata, the DOI configures not simply as an identifying string, but takes the form of a powerful and unambiguous tool for data storage and exchange.
Metadata, as well as the DOI they are associated to, are persistently connected to the object they describe, so they can be easily communicated to other subjects across the productive and distributive chain, enhancing a content producer's ability to trade electronically. Furthermore, metadata represent the key for the development of DOI-based services, such as transnational databases and search engines for different kinds of contents. Asserting that metadata are persistent does not mean they are unmodifiable: registrants may update metadata about their contents any time they wish (whether some publication data change, when the primary URL the DOI resolves to is modified, etc.).
DOIs were developed with a few primary intended benefits:
- Persistent Identification: each DOI unequivocally and permanently identifies the object to which it is associated
- Protection of Intellectual Property: the assignment of a permanent DOI identifier to a work may assist its creator in protecting copyrights to the material
- Network Actionability: through Handle System technology, each DOI resolves to one or more web pages assigned by the publisher
- Semantic Interoperability: metadata allow to unambiguously communicate – to any user, from any place, at any point of the productive/distributive chain – all the pieces of information about the related objects and their hierarchical relationships
International DOI Foundation (IDF)
The International DOI Foundation (IDF), a non-profit organisation created in 1998, is the governance body of the DOI System, which safeguards all intellectual property rights relating to the DOI System.
IDF supports the development and promotion of the Digital Object Identifier system as a common infrastructure for managing content and ensuring the effective respect of copyright. The IDF works 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.
IDF is controlled by a Board elected by the members of the Foundation, with an appointed full-time Director who is responsible for co-ordinating and planning its activities. Through the elected Board, the activities of the Foundation are ultimately controlled by its members. Membership is open to all organizations with an interest in electronic publishing and related enabling technologies.
A DOI Registration Agency (RA) is an authority recognized by the IDF, whose primary role is to provide services to DOI registrants: allocating DOI prefixes, registering DOIs and providing the necessary infrastructure to allow registrants to declare and maintain metadata and state data. RAs are also expected actively to promote the widespread adoption of the DOI, to cooperate with the IDF in the development of the DOI System as a whole and to provide services on behalf of their specific user community.
Currently, eight major RAs are active worldwide, as listed at www.doi.org:
- CrossRef (USA) - website (scholarly only)
- R.R. Bowker (USA) - website (compares DOIs to ISBNs)
- CAL (Australia) - website
- mEDRA (Europe) - website
- Nielsen BookData (UK) - website
- TIB (Germany) - website
- Publications Office (European Union) (EU) - website
- Wanfang Data (China) - website
DOI assignment fees
Unlike non-standardized URL indexing services, which are usually free, there is usually a charge to assign a new DOI. The assignment fees for newly-allocated DOIs can be set arbitrarily by each individual registration agency. Internally, an administrative fee is paid for each allocation by the agency to the IDF.
Notes and references