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ARK (Archival Resource Key) Identifiers
ARKs are URLs designed to support long-term access to information objects. They In 2001 ARKs were introduced to identify objects of any type:
- affordability – there are no fees to assign or use ARKs
- self-sufficiency – you can host ARKs on your own web server, eg, Noid (Nice Opaque Identifiers) open source software
- portability – you can move ARKs to other servers without losing their core identities
- global resolvability – you can host ARKs at a well-known server, such as http://n2t.net/eg, at the N2T.net (Name-to-Thing) resolver
- density – ARKs handle mixed case, permitting shorter identifiers (CD, Cd, cD, cd are all distinct)
Some unique advantages of ARKs:
- simplicity – access relies only on mainstream web "redirects" and ordinary "get" requests
- versatility utility – with "inflections" (different endings), an ARK should access data, metadata, promises, and more
- compatibility – inflections don't conflict with "linked data content negotiation" (a harder and limited way to access metadata)
- versatility – ARKs support persistence statements to describe different kinds of long-term access
- transparency – no identifier can guarantee stability, and ARK inflections help users make informed judgements
- visibility – syntax rules make ARKs easy to extract from texts and to compare for variant and containment relationships
- openness – unlike other persistent identifiers, ARKs don't lock you into one specific, fee-based management and resolution infrastructure
- impact – ARKs appear in Thomson Reuters’ Data Citation Index℠ and ORCID researcher profiles
Since 2001 over 550 organizations spread across fifteen countries registered to assign ARKs. Registrants include libraries, archives, museums , publishers (PeerJSmithsonian), publishers, government agencies (EPA), academic institutions (Princeton), and technology companies (Google). Some of the major users are
- The California Digital Library
- The Internet Archive
- National Library of France (Bibliothèque nationale de France)
- Portico Digital Preservation Service
- University of California Berkeley
- University of North Texas
- University of Chicago
- University College Dublin
- The British Library
We maintain There is a discussion group for ARKs (Archival Resource Keys) at
The group is intended as a public forum for people interested in sharing with and learning from others about how ARKs have been or could be used in identifier applications.
The forum is also intended as a mechanism for the CDL/UC3, in its role as the ARK scheme maintenance agency, to seek community feedback on a number of longer term issues and activities, including
- publishing finalizing the ARK specification as an Internet RFC,
- clarifying local and global resolution options, and
- understanding promoting metadata retrieval in a linked data environment.
- The ARK Identifier Scheme Specification PDF version TXT version
- Towards Electronic Persistence Using ARK Identifiers (July 2003)
- ARK and CDL Identifier conventions
- Archival Resource Key - Wikipedia
- Noid (Nice Opaque Identifiers) open source software for minting and resolving ARKs on your own
- ARK plugin for Omeka that creates and manages ARKs for the Omeka open source web-publishing platform
- EZID service: long term identifiers made easy, if you would rather not install and maintain those services yourself
- N2T.net resolver: Name-to-Thing, a single global resolver at n2t.net
An ARK is represented by a sequence of characters that contains the label, "ark:". When embedded in a URL, it is preceded by the protocol ("http://" or "https://") and name of a service that provides support for that ARK. That service name, or the "Name Mapping Authority" (NMA), is mutable and replaceable, as neither the web server itself nor the current web protocols are expected to last longer than the identified objects. The immutable, globally unique identifier follows the "ark:" label. This includes a "Name Assigning Authority Number" (NAAN) identifying the naming organization, followed by the name that it assigns to the object. Please visit the NAAN request form if you are interested in generating and using ARKs for your information objects.
Here is a diagrammed example:
http://example.org/ark:/12025/654xz321/s3/f8.05v.tiff \________________/ \__/ \___/ \______/ \____________/ (replaceable) | | | Qualifier | ARK Label | | (NMA-supported) | | | Name Mapping Authority | Name (NAA-assigned) (NMA) | Name Assigning Authority Number (NAAN)
The ARK syntax can be summarized,
The NMA part, which makes the ARK actionable (clickable in a web browser), is in brackets to indicate that it is optional and replaceable. ARKs are intended to work with objects that last longer than the organizations that provide services for them, so when the provider changes it should not affect the object's identity. A different provider hosting the object would simply replace the NMA to reflect the new "home" of the object. For example,
The NAAN used above, 13030, represents the California Digital Library. As of 2012, roughly a hundred 2018, over 550 organizations have registered for ARK NAANs, including numerous universities, Google, the Internet Archive, WIPO, the British Library, and other national libraries.
Any stable memory organization may obtain a NAAN at no cost and begin assigning ARKs. Please contact the CDL if you are interested in generating and using ARKs for your information objects.
You can use any system you wish to manage your identifiers. One approach is to create and assign ARKs as a side-effect of deposit into a content repository, with ARKs publicized as being hosted on your server, eg,
Another option is to use the EZID service (http://ezid.cdlib.org), which means your ARKs would appear to be hosted at n2t.net, as in
As with any identifier scheme, persistence requires a redirectable reference to content in stable storage. EZID operates on a cost-recovery basis and can be used to manage your namespace, which includes minting and resolving ARKs (and other identifiers), as well as maintaining metadata. There's is also guidance on CDL Identifier Conventions available.
Because long-term identifiers often look like random strings of letters and digits, organizations typically use software to generate (or mint, in ARK parlance) and track identifiers. To mint ARKs, you may use any software that can produce identifiers conforming to the ARK specification. CDL uses the open-source NOID open source Noid (nice opaque identifiers, rhymes with "employed") software, which creates minters and accepts commands that operate them. The noid software documentation explains how to use noid not only to mint identifiers but also to serve as an institution's "identifier resolver".
ARKs in Action – Inflections
* We regret that the examples in this section are temporarily broken.*
An ARK provides extra services above and beyond that of an ordinary URL. Instead of connecting to one thing, an ARK should connect to three things:
This is a achieved through the use of "inflections", or different kinds of endings. With no ending, the ARK (in a URL) gives you what you expect from a web browser. If you add a single '?' to the end, for example,
erc: who: Dallas (:unavTex.). unavailablePolice Dept. what: [Photographs Truckeeof River,Identification below Truckee Station, looking towards Eastern Summit. -- Photographer's number: 222 -- Photographer's series: Central Pacific Railroad, California. Cards] when: (:unav) unavailable 1963 where: http://arktexashistory.cdlibunt.orgedu/ark:/1303067531/tf5p30086kmetapth346793/
Adding '??' to the end should return a policy statement. It is a side-benefit of ARKs that an object's metadata doesn't need an identifier different from that for the object, which cuts in half the number of identifiers that need to be generated and managed.
There is also information available about CDL Identifier Conventions.