Introduction

The digital object identifier (DOI®¹) system, which was first deployed in 1998, provides an infrastructure for persistent unique identification of objects of any type.

DOI is an initialism for “digital object identifier”, meaning a “digital identifier of an object” rather than an “identifier of a digital object”: DOI is not limited to digital objects and can be used to identify any abstract, physical or non-physical object. In this document, the term “digital object identifier” refers to the system defined in this document, unless otherwise stated.

Objects within the DOI system, i.e. referents, are identified by their DOI names. A DOI name is an opaque string, which does not have a discernible meaning on its own and is for use by humans and machines alike. Each DOI name is registered by a registrant.

To support diverse applications worldwide, a DOI name uses characters from the Unicode character set. More specifically, it can use any Unicode character intended to be written, printed, or otherwise displayed in a form that can be read by humans – formally referred to as a Graphic character.

With this flexibility comes ambiguities when representing or exchanging DOI names. For example:

— the character "Á" (Latin Capital Letter A with Acute) can be encoded either on its own or as the character "A" (Latin Capital Letter A) followed by the combining character ◌́ (Combining Acute Accent);
— multiple schemes (UTF-8, UTF-16 or UTF-32) can be used when serializing a DOI name to bytes for interchange between machines;
— the glyph " Å" can either correspond to the Angstrom Sign or the Latin Capital Letter A with Ring Above.

To avoid these pitfalls, this document specifies the syntax of a DOI name as a sequence of Unicode code points, where each code point is an integer between 0 and 0x10FFFF, and the fundamental unit of encoding in Unicode; and describes several representations appropriate for interchange and visual representation.

The assignment and administration of DOI names is handled by the DOI system, which offers a useful set of functionalities, including:

— persistence, if material is moved, rearranged, or bookmarked,
— interoperability with other data from other sources,
— extensibility by adding new features and services through management of groups of DOI names,
— single management of data for multiple output formats (platform independence),
— class management of applications and services, and
— dynamic updating of metadata, applications and services.

The DOI system is designed to work over the Internet. A DOI name is permanently assigned to an object to provide a resolvable persistent network link to current information about that object, including where the object, or information about it, can be found on the Internet. While information about an object can change over time, its DOI name will not change. A DOI name can be resolved within the DOI system to information related to the identified object such as the location of metadata or a location of the object.

The DOI system enables the construction of automated services and transactions. Applications of the DOI system include, but are not limited to, managing information and documentation location and access; managing metadata; facilitating electronic transactions; persistent unique identification of any form of any data; and commercial and non-commercial services.

An object associated with a DOI name is described unambiguously by system metadata, to support identification and description. The data model supports interoperability between applications.

The scope of the DOI system is not defined by reference to the type of content (format, etc.) of the referent, but by reference to the functionalities it provides and the context of use. The DOI system provides, within networks of DOI applications, for unique identification, persistence, resolution, metadata and interoperability with other identifier schemes.