ARK Alliance

Home of the Archival Resource Key (ARK)

Comparing ARKs, DOIs and other identifier systems

Reasons to use ARKs as compared to DOIs

What ARK, DOI, Handle, PURL, and URN have in common

These are the major persistent identifier types (or schemes).

They also have very similar structure, as seen in the examples below, consisting of four parts:
  1. the protocol (https://) plus a hostname,
  2. just for ARK and URN, there’s also a label (“ark:” or “urn:”),
  3. the name assigning authority (99999, 10.99999, or 99999), which is the organization or group that created a particular identifier,
  4. and finally, the name, or local identifier, that it assigned (12345).

As noted earlier, to be persistent, all types of identifiers require persistent maintenance as you change or migrate your systems, and they are all subject to some of the same risks:

Given how little the schemes do for you, when choosing one you’ll likely want to consider factors such as cost, risk, and openness.

How ARKs differ from identifiers like DOIs, Handles, PURLs, and URNs

ARKs are the only mainstream, non-siloed, non-paywalled identifiers that you can register to use in about 48 hours. DOIs, Handles, and PURLs require that resolution and other services come from their respective centralized systems (silos).

That’s not to say that persistence is free. Making any identifier persistent burdens you, the provider, with the costs of content management, hosting, monitoring, and forwarding. You can do those things yourself or with help from a vendor. But with ARKs, just as with URLs, you will not be charged separately for your identifiers and you will not be locked in to a special-purpose resolution silo that also locks out other identifiers.

ARKs are unusual in being decentralized. While one can get resolution services from a global ARK resolver called, over 90% of the ARKs in the world are published without using in the URL hostname. More than 650 registered ARK organizations across the world have, between them, created an estimated 8.2 billion ARKs, and, as with URLs, no one has ever paid an identifier fee to create them. Of course maintaining them isn’t free. It is never without cost to keep content access persistent in the long term, regardless of identifier type.

More differences between ARKs, DOIs, Handles, PURLs, and URNs

Using multiple identifier systems

You may choose to use two identifier systems for some resources, although it can become confusing when it happens often. Many people start by assigning ARKs to each thing they create in order to have a stable reference right from the beginning, even before they know whether they want to publish it, let alone keep it.

The object and its metadata develop together, and 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 support a proper DOI. This is a way in which ARKs support early object development.

To support two identifiers efficiently, it is recommended that you create the DOI such that it redirects to the original ARK. This not only eliminates the need ever to update the DOI redirection, but it also keeps the ARK persistent for anyone who previously recorded or bookmarked it.

When to use ARKs compared to DOIs, Handles, PURLs, or URNs

Nothing inherent in ARKs, DOIs, Handles, PURLs, or URNs makes them more or less fit for any particular field, domain, or sector. With an identifier resolver and administrative management service, they all provide the core service of resolution.

Generalizations about identifier types sometimes apply when resolution and management for that type is locked into one particular vendor or provider. For example, many PURL and Handle features and restrictions are well-defined by their respective administration silos, as are those of DOIs, which are built on top of Handles. But DOIs have metadata practices that are diverse and evolving across different DOI registration agencies.

The concrete differences that we experience, such as metadata, landing pages, and tool integration (eg, publishing tools), are not properties of identifier schemes per se, but properties of resolution, management, and citation services that various providers extend to or withhold from different identifier types. Those services are shaped in turn by communities of practice and by markets. Basic services are founded on a reliable database storing each identifier along with metadata elements (creator, title, date, redirection URL, etc) that describe the identified object. Extra services include link checking, duplicate detection, report generation, and searching.