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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, such as http://n2t.net/eg, at the N2T (Name-to-Thing) resolver
  • density – ARKs handle mixed case, permitting shorter identifiers (CD, Cd, cD, cd are all distinct)

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In the last fourteen years over 317 395 organizations spread across fifteen countries registered to assign ARKs.  Registrants include libraries, archives, museums (Smithsonian), publishers (PeerJ), government agencies (EPA), academic institutions (HarvardPrinceton), and technology companies (Google). Some of the major users are

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Here is a diagrammed example:

Code Block
xml
xml
    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,

Code Block
xml
xml
   [http://NMA/]ark:/NAAN/Name[Qualifier]

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,

Code Block
xml
xml
   http://bnf.fr/ark:/13030/tf5p30086k

might become

Code Block
xml
xml
   http://portico.org/ark:/13030/tf5p30086k

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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,

Code Block
xml
xml
   http://myrepo.example.org/ark:/12345/bcd987

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

Code Block
xml
xml
   http://n2t.net/ark:/12345/bcd987

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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 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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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,

Code Block
xml
xml
   http://texashistory.unt.edu/ark:/67531/metapth346793/?

it returns a brief machine- and eye-readable metadata record; in this case, an Electronic Resource Citation (ERC) using Dublin Core Kernel metadata., such as

Code Block
xml
xml

erc:
who: Dallas (Tex.). Police Dept.
what: [Photographs of Identification Cards]
when: 1963
where: http://texashistory.unt.edu/ark:/67531/metapth346793/

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