An Archival Resource Key (ARK) is a Uniform Resource Locator (URL) that is a multi-purpose identifier for information objects of any type. An ARK contains the label ark: after the URL's hostname, which sets the expectation that, when submitted to a web browser, the URL terminated by '?' returns a brief metadata record, and the URL terminated by '??' returns metadata that includes a commitment statement from the current service provider. The ARK and its inflections ('?' and '??') gain access to three facets of a provider's ability to provide persistence.
Implicit in the design of the ARK scheme is that persistence is purely a matter of service and not a property of a naming syntax. Moreover, that a "persistent identifier" cannot be born persistent, but an identifier from any scheme may only be proved persistent over time. The inflections provide information with which to judge an identifier's likelihood of persistence.
- NAAN: Name Assigning Authority Number - mandatory unique identifier of the organization that originally named the object
- NMAH: Name Mapping Authority Host - optional and replaceable hostname of an organization that currently provides service for the object
- Qualifier: optional string that extends the base ARK to support access to individual hierarchical subcomponents of an object, and to variants (versions, languages, formats) of components.
Name Assigning Authority Numbers (NAANs)
A complete NAAN registry is maintained by the California Digital Library and replicated at the Bibliothèque Nationale de France and the US National Library of Medicine. In 2011 it contained over 80 entries, some of which appear below.
- 12025: National Library of Medicine
- 12148: Bibliothèque Nationale de France
- 13030: California Digital Library
- 13038: World Intellectual Property Organization
- 13960: Internet Archive
- 15230: Rutgers University
- 17101: Centre for Ecology & Hydrology, UK
- 20775: University of California San Diego
- 21198: University of California Los Angeles
- 25031: University of Kansas
- 25593: Emory University
- 26677: Library and Archives Canada
- 27927: Portico/Ithaka Electronic-Archiving Initiative
- 28722: University of California Berkeley
- 29114: University of California San Francisco
- 39331: National Library of Hungary
- 52327: Bibliothèque et Archives Nationales du Québec
- 61001: University of Chicago
- 62624: New York University
- 64269: Digital Curation Centre
- 65323: University of Calgary
- 67531: University of North Texas
- 78319: Google
- 78428: University of Washington
- 80444: Northwest Digital Archives
- 81055: British Library
- 88435: Princeton University
Three generic ARK services have been defined. They are described below in protocol-independent terms. Delivering these services may be implemented through many possible methods given available technology (today’s or future).
Access Service (access, location)
- Returns (a copy of) the object or a redirect to the same, although a sensible object proxy may be substituted (for instance a table of contents instead of a large document).
- May also return a discriminated list of alternate object locators.
- If access is denied, returns an explanation of the object’s current (perhaps permanent) inaccessibility.
Policy Service (permanence, naming, etc.)
- Returns declarations of policy and support commitments for given ARKs.
- Declarations are returned in either a structured metadata format or a human readable text format; sometimes one format may serve both purposes.
- Policy subareas may be addressed in separate requests, but the following areas should be covered:
- object permanence,
- object naming,
- object fragment addressing, and
- operational service support.
- Returns a description of the object. Descriptions are returned in either a structured metadata format or a human readable text format; sometimes one format may serve both purposes.
- A description must at a minimum answer the who, what, when, and where questions concerning an expression of the object.
- Standalone descriptions should be accompanied by the modification date and source of the description itself.
- May also return discriminated lists of ARKs that are related to the given ARK.
- Digital Object Identifier (DOI)
- Handle System (Handle)
- Persistent Uniform Resource Locator (PURL)
- Uniform Resource Name (URN)
Notes and references
- Hierarchy qualifiers begin with a slash character.
- Variant qualifiers begin with a dot character.
- Name Assigning Authority Number registry