ARK (Archival Resource Key)

What is ARK?

ARK (Archival Resource Key) is an identifier scheme conceived by the California Digital Library (CDL), aiming to identify objects in a persistent way. These objects can be of any type — physical (table, book), digital (digitized book…) or even immaterial (concepts, …)

The ARK scheme: structure and organization

An ARK identifier complies with the following structure:
Scheme of the structure of an ARK identifier
The Name Mapping Authority Host (NMAH) is a service whose task is to resolve ARK identifiers, that is, to make an ARK identifier “actionable” by dereferencing the object it identifies and/or the description of this object.

The persistent part of the identifier is composed of the identifier type, the name assigning authority number (NAAN) and the ARK name itself; in the example above, it is the "ark:/12148/bpt6k107371t" character string.
  • The "ark" identifier type, or scheme, declares that this is an ARK identifier.
  • The Name Assigning Authority Number (NAAN) identifies an institution which has been authorized to assign ARKs. This 5-digit number, unique within the "ark:" scheme, is freely assigned by the California Digital Library to any institution that asks for it. The California Digital Library maintains these numbers and guarantees their uniqueness. Each NAAN is recorded in the NAAN registry.
  • The ARK name is an opaque identifier assigned by the Name Assigning Authority. It can be composed of prefixes allowing to group sets of resources according to criteria left to the Name Assigning Authority’s discretion. The ARK name is composed of a string of alphanumeric characters without vowels. It is recommended, although not mandatory, to end the ARK name by a check character.
Qualifiers are suffixes that allow one to narrow his request on a document. There are two types of qualifiers:
  • Hierarchy qualifiers, beginning with a "/", allow one to ask for a part of the object (e.g. the page of a document. They immediately follow the ARK name;
  • Service qualifiers, beginning with a ".", allow one to access a particular variant of a document and/or a particular service on it (particular dissemination type or version of the identified document…)
Those qualifiers are defined and maintained by the name assigning authority, that supports their consistency, and are interpreted by the name mapping authority. When used simultaneously with a granularity qualifier, service qualifiers must occur after it.
This global structure shows shared responsibilities between :
  • The CDL, that maintains the ARK scheme and the NAAN registry in particular,
  • The name assigning authorities, that maintain their ARK names and the qualifiers they defined,
  • The name addressing authorities, that provide the resolution of ARK identifiers and implement the qualifiers.
This sharing of responsibilities is the key to the persistency of ARK identifiers.

A copy of the name assigning authority registry at BnF

The name assigning authority registry, that guarantees the global uniqueness of an ARK identifier assigned by a name assigning authority, is the cornerstone of the ARK system and guarantees its viability.
It is thus central to guarantee its persistency. For that purpose, the BnF is keeping a backup copy of the registry.

ARK implementation at BnF

ARK is currently used at BnF for two kinds of resources:

Thursday, February 27, 2014


Sébastien Peyrard
Bibliographic and Digital Information Department