THIS IS AN OLD VERSION. HERE IS THE LATEST ARKs FAQ.

Basics

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is 12148, and it uniquely identifies the French National Library. Each NAAN is associated with the URL of a resolver for its ARKs, for example, to resolve 12148 ARKs, append them to https://gallica.bnf.fr/ as shown in above. The N2T.net resolver is unusual in that it routes any ARK to the resolver registered under its NAAN.

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To anything digital, physical, or abstract. That can include things that don't yet exist but to which you need to refer from objects that you're in the process of creating or planning, such as a link from a draft article to a dataset under preparation, or a link from an archived digital letter to a planned finding aid.

One caution is that you should generally assign ARKs to things that you own, control, or manage. Assigning ARKs to things you don't control is discouraged because such identifiers tend to be fragile.

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You are free to create ARK strings as you wish, provided you use only digits, letters upper- and lower-case letters (ASCII, no diacritics), and the following characters:

= ~ * + @ _ $ . /

The last two characters are reserved in the event you wish to disclose ARK relationships. A unique feature of ARKs is that hyphens ('-') may appear but are identity inert, meaning that strings that differ only by hyphens are considered identical; for example, these strings

ark:/12345/141e86dc-d396-4e59-bbc2-4c3bf5326152

ark:/12345/141e86dcd3964e59bbc24c3bf5326152

identify the same thing. The reason for this feature is that text formatting processes out in the world routinely introduce extra hyphens into identifiers, breaking links to any server that treats hyphens as significant.

Regarding assignment strategy, it is common to leverage legacy identifiers. For example, a museum moth specimen number cd456_f987 might be advertised under the ark:/12345/cd456_f987. Some legacy identifiers may need to be altered in view of ARK character restrictions.

The second common strategy is to make up entirely new strings for your ARKs. In this case it is important to consider whether to make them opaque or non-opaque (or a bit of both). 

What are opaque identifiers?

Persistent identifier strings are typically opaque, deliberately revealing little about what they're assigned to, because non-opaque identifiers do not age or travel well. Organization names are notoriously transient, which is why NAANs are opaque numbers. As titles and dates are corrected, word meanings evolve (eg, innocent older acronyms may become offensive or infringing), strings meant to be persistent can become confusing or politically challenging. The generation and assignment of completely opaque strings comes with risk too, for example, numbers assigned sequentially reveal timing information and strings containing letters can unintentionally spell words. 

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ARKs are not required to be opaque, but it is recommended that the base object name be made opaque, since it tends to name the main focus of persistence. If any qualifier strings follow that name, it may be less important that they be opaque. To help decide what your approach to opacity, you may wish to consider compatibility with legacy identifiers and ease of string generation and transcription (eg, brevity, check digits). New strings can be created (minted) with date/time, UUID, and number generators, as well as Noid (Nice Opaque Identifiers) minters. 

Opaque strings are "mute" and therefore challenging to manage, which is why ARKs were designed to be "talking" identifiers. This means that if there's metadata121962566, an ARK that comes in to your server with the '?' inflection should be able to talk about itself.

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servingARKs servingARKs

How do I make server content addressable with ARKs?

First, decide what the user experience of accessing your ARKs will be, for example, a spreadsheet file, a PDF, an image, a landing page filled with formatted metadata and a range of choices, etc. Whichever you choose, plan for your server to be able to respond with metadata if your ARK should arrive with a '?' inflection after it.

Otherwise, serving ARKs is like serving URLs. Normally incoming URL strings address (get mapped to) content that your web server returns. If your server is ARK-aware, incoming ARKs (expressed as URLs) must be mapped to the same content. A common approach is to map the ARK to the URL using a software table that you update whenever the URL changes. In this case your server is acting as a local resolver. If you don't want to implement this yourself, there are ARK software tools and services that can help.

Another approach is to run your web server without change, but instead of updating local tables, you would update ARK-to-URL mapping tables residing at a non-local resolver. Examples of this can be found among vendors and in any organization that updates tables via EZID.cdlib.org (which, due to a special relationship, updates resolver tables at n2t.net).

How do I advertise my ARKs?

An ARK meant for external use is generally advertised (released, published, disseminated) as an actionable identifier, in other words, inside a full URL starting with https:// as in the examples above. A more compact visual display of an actionable ARK starting with ark:/ can be achieved with an HTML hyperlink such as

<a href="https://n2t.net/ark:/99166/w66d60p2">ark:/99166/w66d60p2</a>

An important decision is whether your URL-based ARKs will use the hostname of your local resolver or the N2T.net resolver. If local control or branding is important enough, you would advertise ARKs based at your local resolver. If you're concerned about the stability of your local hostname, you would advertise your ARKs based at n2t.net (see examples of both).

Resolving your ARKs through N2T is always possible for users, regardless of how you advertise them.

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N2T uses two kinds of stored data. First, it stores individual records for over 20 million object identifiers (eg, ARKs, DOIs) that it obtains from three sources: EZID.cdlib.org, Internet Archive, and YAMZ.net. When such records include a redirection URL (target) and descriptive metadata121962566, N2T can act on inflections121962566 as well as perform suffix passthrough and "content negotiation".

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Yes, ARKs can be assigned at any level of granularity, such as to a manuscript, to chapters inside it, to chapter sections, subsections, etc. An ARK can also be assigned to a thing that encloses other things. In ARKs the character '/' is reserved to help the recipient understand about containment, for example, the first ARK below contains the second ARK:

                            ark:/12148/btv1b8449691v

                            ark:/12148/btv1b8449691v/f29

That's the containment qualifier. There's only one other ARK qualifier, and it indicates variant forms of a thing by using the reserved character '.' in front of a suffix. For example, if these ARKs identify documents,

                            ark:/12148/btv1b8449691v/f29.pdf

                            ark:/12148/btv1b8449691v/f29.html

because they differ only by the suffix .pdf or .html, it can be inferred that they identify two different forms of the same document.

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You can change a NAAN by filling out the same online form used for requesting a new NAAN. Example reasons for a change may include

• notifying N2T that your organization's contact person or resolver URL will change,
• updating your organization's name assignment policy (sample policy),
• requesting an additional NAAN for a significant new body of ARKs or new organizational division, and
• transitioning your NAAN to another organization that will carry on your work and take over your NAAN.

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• To keep costs down.
• To work with exactly the metadata you want.
• To be able to create identifiers without metadata.
• To be able to create an identifier even before your object exists.
• To have an identifier as soon as you create the first draft of your data.
• To hold that identifier private while the data and metadata evolve, and decide (maybe years) later, to publish or discard it.
• To retain that identifier upon publication, perhaps then assigning an additional identifier, such as a DOI.
• Because ARKs, built for generic application and not publication, fit naturally into identifying physical samples and field stations.
• Because they won't break as text formatting processes out in the world routinely introduce hyphens into identifiers.
• To be able to change vendor and/or infrastructure without having to coordinate database transfers with a central authority.
• To be able to create a larger number of identifiers of a given length, since mixed case letters permit denser strings.
• To be able to deal with the namespace splitting problem without losing control of your identifiers.
• To link identifiers to different kinds of nuanced persistence commitments.
• To be able to add queries (eg, ?lang=en) when resolving your identifiers.
• To use open infrastructure consistent with your organization's values.
• To link directly to the objects you value instead of to landing pages.
• To create one identifier that enables millions (suffix passthrough).
• To access convenient, full-function metadata via inflections 121962566.

What does ARK have in common with DOI, Handle, PURL, and URN?

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• Landing pages: Crossref and DataCite DOIs link to publisher landing pages constructed around but not directly to objects you care about, but ARKs can freely link directly to objects you care about, which is machine- and human-friendly since it does not require an extra human navigation step for common tasks such as
  • opening an article's PDF file for reading,
  • referencing an image file meant to be incorporated automatically inline into a document, and
  • citing a spreadsheet to be used for direct data analysis by software.
• DOIs, Handles, etc. do not support ARK-style inflections121962566 that permit access to metadata regardless of whether an identifier points to an object or its landing page.
• Unlike DOIs and Handles, ARKs don't have metadata requirements. ARKs that haven't been released into the world are easy to delete.
• All things eventually pass, including hostnames and the web itself and the "https://" protocol. When that first part of the identifier ceases to have meaning, only ARKs and URNs will include the label (eg, "ark:") indicating the type of identifier that remains.
• For DOIs, Handles, and PURLs, you are required to use their respective resolvers. ARKs and URNs, permit you to use your own resolver.
• To create DOIs and Handles, you are required to pay a membership fee and, for DOIs, per-DOI charges. There are no fees for ARKs, PURLs, and URNs.
• To create Handles, you are required to install and maintain a local Handle server, which gives you another system to monitor, patch, and troubleshoot.
• Although you can use a local or vendor resolver for your ARKs and URNs, ARKs can be resolved via the global n2t.net resolver.
• The envisioned URN resolution infrastructure was never built, so URNs are currently resolved as URLs, and there is no designated global URN-as-URL resolver. In order to register to create URNs, you must apply for a URN namespace.
• ARKs have some unique features that support early object development: ARKs can be deleted, can be born with no metadata, and can exist with any metadata you care to store. 

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Starting with an ARK, you benefit from being able to keep the original identifier from birth through to public release as the object and its metadata matures. For the subset of things that you end up wanting to publish in places that require DOIs, you can assign DOIs at publication time. If your ARK is stable and has basic metadata, you're already doing everything you need to have a proper DOI. This is a way in which ARKs support early object development.

In such a scenario, to reduce the burden of maintaining both identifiers you could register the DOI to redirect to the ARK. At the cost of maintaining just one identifier (the ARK), this would keep newly published links and links previously stored and bookmarked by your collaborators from breaking.

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Creating metadata (extra information associated with or describing an object) has several key benefits. First, no matter what the ARK redirects to – whether a landing page or a file – metadata gives users vital information about the object, such as references to newer versions, creation date, provenance, etc. For ARKs typically metadata is accessed via inflections121962566.

Metadata really eases the difficulty of working with opaque identifiers, which reveal no clues as to what they identify. In the absence of metadata you are forced to access the object itself to remind yourself what it is, and also to trust that you're accessing the correct object. Moreover, discrepancies between returned metadata and the accessed object help everyone detect identifier changes and errors. 

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