An Archival Resource Key (ARK) is a Uniform Resource Locator (URL) that is a multi-purpose persistent 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.
ARKs can be maintained and resolved locally using open source software such as Noid (Nice Opaque Identifiers) or via services such as EZID and the central N2T (Name-to-Thing) resolver.
[http://NMAH/]ark:/NAAN/Name[Qualifier]
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.
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 2015 it contained over 395 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
14023: Revista de Arte, Ciência e Comunicação
15230: Rutgers University
17101: Centre for Ecology & Hydrology
20775: University of California, San Diego
21198: University of California Los Angeles
25031: University of Kansas
25593: Emory University
25652: École nationale supérieure des mines de Paris
26677: Library and Archives Canada
27927: Portico/Ithaka Electronic-Archiving Initiative
28722: University of California Berkeley
29114: University of California San Francisco
35911: IEEE
39331: National Library of Hungary
45487: Russian Linguistic Bulletin (Российский Лингвистический Бюллетень)
48223: UNESCO
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
87925: University College Dublin
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).
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.
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.
