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Ark & Noid (module for Omeka S)

New versions of this module and support for Omeka S version 3.0 and above are available on GitLab, which seems to respect users and privacy better than the previous repository.

Ark & Noid is a module for Omeka S that creates and manages ark identifiers. They can be used in urls the admin and the public sides with the module Clean Url.

The ark identifiers can replace the default cool URIs of each record, that corresponds to the simple number of a row in a table of the database.

Arks are short, opaque, meaningless, universal, unique and persistent ids for any records. The acronym "ark" means "Archival Resource Key". This is a reference to the Noah’s ark (digital documents will have a long life) and to the world of archives (Omeka can be an institutional archive) too. Optionally, the identifiers can be resolved via a service as N2T, the Name-to-Thing Resolver.

Arks may be built with the utility Noid, that creates nice opaque identifiers, that is integrated too via the library Noid4Php.

See a living example in the bibnum of PSL or in Bibliothèque patrimoniale of Mines ParisTech.

If you don’t have an authority number, the plugin will create a non standard ark, but nevertheless a unique and opaque identifier that can be managed.

Presentation of Ark

A full ark looks like (official example):
    \________________/ \__/ \___/ \______/ \____________/
      (replaceable)     |     |      |       Qualifier
           |       ARK Label  |      |    (NMA-supported)
           |                  |      |
 Name Mapping Authority       |    Name (NAA-assigned)
          (NMA)               |
                   Name Assigning Authority Number (NAAN)

In Omeka, by default, the ark of an item looks like:

The "12025" is the id of the institution, that is assigned for free by the California Digital Library to any institution with historical or archival purposes. The "b6KN" is the short hash of the id, with a control key. The name is always short, because four characters are enough to create more than ten millions of unique names.

In the Ark format, a slash "/" means a sub-resource or a hierarchy and a dot "." means a variant, so each file gets its ark via the qualifier part (its order by default, but the original filename or the Omeka hash can be used):

Arks for derivatives files are represented as:

Currently, the links to physical files are created via the standard function record_url() and the type of derivative, as record_url($file, 'original'):

The format of the name can be customized with a prefix (recommended), a suffix and a control key (recommended too). The qualifier part is not required to be opaque. Advanced schemas can be added via the filters "ark_format_names" and "ark_format_qualifiers", associated classes and routes.

So the name can be obtained too from another tool used to create and manage arks, like NOID, a generator of "nice opaque identifiers". This is useful too if other unique ids or permanent urls are already created via free or commercial systems PURL, DOI, Handle, etc. (see the full CDL example):   <----  Example Key
                                doi:10.30/tqb3kh97gh8w         with parallel
                                hdl:13030/tqb3kh97gh8w        parts in other
                                urn:13030:tqb3kh97gh8w          id schemes.

For more informations about persistent identifiers, see this overview. The full specification of ark can be checked too.

All arks are saved as Dublin Core Identifier, as recommended. This allows to make a check to avoid duplicates, that are forbidden. This applies to collection and items. For files, the qualifier part is managed dynamically.

The policy is available at "" and "".

Ark can be displayed by default instead of the default internal ids. This plugin is fully compatible with Clean Url: an ark can be used for machine purposes and a clean url for true humans and for the natural referencement by search engines.

Presentation of Noid

NOID allows to create nice opaque identifier, to bind it to an object (the url here), and to manage them in the long term. Only the template is explained here.

  • A template is formed by :

    • a prefix that defines a subset, a list of ark minted by a subpart of an organization, or a specific set (may be empty, or commonly 1 to 5 characters).
    • a .,
    • a mode: s for sequential, z for unlimited sequential, or r for random,
    • a mask: composed from one or more of these character repertoires: d, e, i, x, v, E, w c and l (see below).
    • and finally a k (key for control), if wanted.
  • The character repertoires are:

    • Standard:
      • d: { 0-9 x } cardinality 10
      • e: { 1-9 b-z } - {l, vowels} cardinality 29
    • Proposed:
      • i: { 0-9 x } cardinality 11
      • x: { 0-9 a-f _ } cardinality 17
      • v: { 0-9 a-z _ } cardinality 37
      • E: { 1-9 b-z B-Z } - {l, vowels} cardinality 47
      • w: { 0-9 a-z A-Z # * + @ _ } cardinality 67
    • Proposed, but not accepted for Ark:
      • c: Visible ASCII - { % - . / \ } cardinality 89
    • Not proposed in the Perl script, but compatible with Ark and useful because the longest with only alphanumeric characters:
      • l: { 0-9 a-z A-Z } - { l } cardinality 61

The prime cardinality allows to set an efficient check character (k) against a single-character error and a transposition of two single characters.

So, a template like a.rlllk allows to create a fixed-size noid for 226981 records and the template b.rllllk allows to create 13845841 noids: large enough in most cases.

The default template in Omeka is .zek: unlimited number of sequential names, with a control key, like 12345/92 and 12345/bkp6 for the NAAN 12345.

See other templates for more explanation and examples.


The module uses an external library, Noid, so use the release zip to install it, or use and init the source.

The module only creates ark identifier. To use them as url in public site or in admin, use the module Clean Url.

  • From the zip

Download the last release from the list of releases (the master does not contain the dependency), and uncompress it in the modules directory.

  • From the source and for development

If the module was installed from the source, rename the name of the folder of the module to Ark, go to the root module, and run:

composer install --no-dev


Don't forget to save the noid database, located in /files/arkandnoid by default.


With the format "Omeka Id", the php extension "BCMath" must be enabled. This is the case on the majority of the servers (based on Debian or Windows), else install the module "php-bcmath", or don’t use this format.

With the format "Noid for php", the plugin requires the php extension "dba", that uses to be installed by default with Php, and the BerkeleyDB library, that is installed by default too on standard web servers and any Linux distribution (package libdb5.3 on Debian), because it is used in many basic tools.

Perl and php

The output of perl (release 5.20 and greater) and php (before and since release 7.1, where the output of rand() and srand() were fixed in the php algorithm), are the same for integers at least until 32 bits (perl limit, namely more than 4 000 000 000 identifiers).

Anyway, it is recommended to use php 7.1 or higher, since previous versions of php are no more supported.

Automatic test

For testing and debugging, phpunit 5.7 is required. If you don’t have it:

cd tests
php phpunit-5.7.phar


Ark ids are automatically added as identifiers when a collection or an item is saved.

Because an ark should be persistent, if an ark exists already, it will never be removed or modified automatically. Nevertheless, if it is removed, a new one will be created according to the specified scheme. Note that the default internal format create unique ids based on the Omeka id, so the same is created if the parameters are the same.

To set arks to existing records, simply select them in admin/items/browse and batch edit them, without any change.

You can run the command line tool too (not integrated in Omeka S version currently):

php -f modules/Ark/create_arks.php


Even if a check is done after creation of an ark to avoid any duplicate, it’s not recommended to change parameters once records are public in order to keep the consistency and the sustainability of the archive.


  • Integrate the script to create arks from Omeka 2.
  • Manage the policy statement by item.
  • Let the choice to link ark to the file or to the record.
  • Integrate the new composer package to create noids with xml or sql.


Use it at your own risk.

It’s always recommended to backup your files and your databases and to check your archives regularly so you can roll back if needed.

Don't forget to save the noid database, located in /files/arkandnoid by default.


See online issues on the module issues page on GitLab.


This module is published under the CeCILL v2.1 license, compatible with GNU/GPL and approved by FSF and OSI.

In consideration of access to the source code and the rights to copy, modify and redistribute granted by the license, users are provided only with a limited warranty and the software’s author, the holder of the economic rights, and the successive licensors only have limited liability.

In this respect, the risks associated with loading, using, modifying and/or developing or reproducing the software by the user are brought to the user’s attention, given its Free Software status, which may make it complicated to use, with the result that its use is reserved for developers and experienced professionals having in-depth computer knowledge. Users are therefore encouraged to load and test the suitability of the software as regards their requirements in conditions enabling the security of their systems and/or data to be ensured and, more generally, to use and operate it in the same conditions of security. This Agreement may be freely reproduced and published, provided it is not altered, and that no provisions are either added or removed herefrom.


  • Copyright Daniel Berthereau, 2015-2023 (see Daniel-KM on GitLab)
  • Copyright BibLibre, 2016-2017

First version of this plugin has been built for Mines ParisTech. The upgrade for Omeka S has been built for Paris Sciences et Lettres (PSL) by BibLibre.


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