A digital object identifier (DOI®) is a method of uniquely identifying documents and other types of content in digital form. Under the system, content is assigned a non-changing identifier called a DOI® name. This name can be assigned to different types of content, such as electronic documents, graphics, and software, and can be used in conjunction with other identifiers. As a result, DOI® names can also be “resolved” to provide additional information. The International DOI® Foundation (IDF) maintains the system and grants other organizations the right to assign names.
By the time the IDF was formed in 1998, it was clear that existing identifiers couldn’t adequately bridge the gap between electronic and print sources. Documents with similar titles, for example, could be confused if referred to by name only, and an item’s Uniform Resource Locator (URL) became useless if the item was moved or deleted. Unique numbering schemes, such as the International Standard Book Number (ISBN), could be used, but didn't provide an easy way to locate the content online. The digital object identifier system was conceived as way to address some of these issues as well as add new functionality powered by digital technology.
At the heart of the digital object identifier system is a character string, or string of letters and numbers, called a DOI® name. A unique DOI® name is assigned to each piece of content that uses the system. These names are designed to be persistent; while a title or location on the web may change, its DOI name® will remain the same. This is especially important in academic fields; for this reason, a number of style guide authors like the American Psychological Association (APA) now recommend using DOI® names in bibliographies and citations.
A variety of different content — from software to graphics within a text article — can use the digital object identifier system. The IDF does not define an object's necessary size or scope in order to be assigned a DOI® name, however. An academic journal, for example, might have a name assigned to each issue, to each article within an issue, or even to something as specific as a data table within an article. The IDF also allows a great deal of flexibility in the structure of DOI® names themselves, so an existing identifier can be used. Publishers of scientific journals, for example, may use an identifier called the Publisher Item Identifier (PII) when creating a DOI® name, thereby allowing compatibility between the two systems.
Unlike identifiers found in other cataloging systems, however, the DOI® system can provide additional information through the Internet. In a process known as resolution, a DOI® name is sent to an online service that responds with a metadata about the content. This metadata can include the name, author, date published, and even a location on the web where the content can be found. Metadata can be changed if the content is updated, but the DOI® itself should remain the same.
Most DOI® names are not issued directly by the IDF but by outside registration agencies that assign names to various customers. The agencies pay operational fees to the IDF, which oversees and maintains the digital object identifier system. The IDF has also been successful in getting the DOI® system approved as an official standard by various standards-setting organizations around the world.