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ARKs are URLs designed to support long-term access to information objects. They In 2001 ARKs were introduced to identify objects of any type:

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  • 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, 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
  • utility – with "inflections" (different endings), an ARK should access data, metadata, promises, and more
  • versatility 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 (and DOIs) appear in Thomson Reuters’ Data Citation Index℠

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  • and ORCID researcher profiles

Since 2001 over 550 organizations spread across fifteen countries registered to assign ARKs.  Registrants include libraries, archives, museums (Smithsonian), publishers (PeerJ), 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

       httphttps://groups.google.com/group/arks-forum

 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.

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ARK Anatomy

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:

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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.

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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

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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 (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".

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There is also information available about CDL Identifier Conventions.