Archival Resource Key
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.
- 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 2015 it contained over 395 entries, some of which appear below.
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.
Notes and references
- ^ Hierarchy qualifiers begin with a slash character.
- ^ Variant qualifiers begin with a dot character.
- ^ Name Assigning Authority Number registry
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