What are ARKs?
ARKs (Archival Resource Keys) are high-functioning identifiers that lead you to things and to descriptions of those things. For example, this ARK,
https://n2t.net/ark:/67531/metadc107835/
gets to a dissertation, and adding a '?' to the ARK gets you to its description:
https://n2t.net/ark:/67531/metadc107835/?
What's an identifier?
On the internet, an identifier is a URL, or part of a URL. For example, this basic ARK identifier,
is part of two different URLs (Uniform Resource Locators), also known as web links or web addresses:
https://gallica.bnf.fr/ark:/12148/btv1b8449691v/f29
https://n2t.net/ark:/12148/btv1b8449691v/f29
ARKs are especially good at being persistent identifiers.
What's a persistent identifier?
The average lifetime of a URL has been said to be 44 days. At the end of its life, a URL link breaks, which means it gives you the dreaded "404 Not Found" error. As irritating as it is – and most of us have seen it happen – it's a disaster for libraries, archives, museums, and other memory organizations. A persistent identifier (sometimes abbreviated to PID) is an identifier that in principle will continue to work far into the future, even as things move between websites. Normally when things move, we're burdened with broken links and having to learn to use their new URLs (links), and that's where identifier resolvers come in.
What's a resolver?
A resolver is a website that is especially good at forwarding an incoming identifier (the one originally advertised to users) to whatever website is currently best suited to deal with it. To make it work, the hostname of the resolver itself is carefully chosen so that it never has to be changed. Memory organizations, some of them centuries old, tend to have website hostnames that are especially stable as resolvers. Other well-known resolvers include n2t.net, identifiers.org, doi.org, handle.net, and purl.org.
How do ARKs differ from DOIs, Handles, PURLs, and URNs?
Here's the short answer. These are all major kinds of persistent identifiers. Among them, ARKs are the only mainstream, non-siloed, non-paywalled identifiers that you can register to use in about 24 hours. Over 500 registered organizations have created an estimated 3.2 billion ARKs in the world, and no one has ever paid for the right to create them.
Is there a longer answer to that question?
First, let's dispense with what these identifiers have in common. Their resolvers all forward using ordinary web redirection and they have similar structure. In these examples,
https://n2t.net/ark:/99999/12345
https://doi.org/10.99999/12345
https://handle.net/10.99999/12345
https://purl.org/12345
https://???/urn:99999:12345
there's always the protocol (https://) plus a hostname, followed by the Name Assigning Authority (99999, 10.99999, or purl.org), which is the organization that created the identifiers. Finally there's the name, or local identifier, that it assigned (12345).
So how do these identifiers differ? Here's a short list.
- When (not if, since all things pass) the https:// protocol and the hostname cease to exist, only ARKs and URNs will still indicate the kind of identifier that remains.
- To create DOIs, Handles, and PURLs, you are required to use their respective resolvers. There are no such silos with ARKs and URNs, for which you can use your own resolver.
- To create DOIs and Handles, you are also required to pay a membership fee and per-DOI charges. There are no such paywalls for ARKs, PURLs, and URNs.
- It is hard to generalize how people use these identifiers. DOIs, for example, used to be known primarily as identifiers for scientific and scholarly publications, with a mature community and service offering around "Crossref DOIs", but since 2013 enough new assigners have joined that it is hard to make generalizations about DOIs.
- Although you can use your own or a vendor resolver for your ARKs, all ARKs can be resolved via n2t.net. Thus n2t.net is the closest thing to a "global ARK resolver".
- For URNs there is no single global resolver, and in order to register as a Name Assigning Authority you must apply for a URN namespace.
Don't they differ in metadata flexibility, content negotiation, inflections, and suffix passthrough?
Only one resolver, n2t.net, supports all of these features, and it does so for any identifier stored with appropriate metadata. Contrary to popular belief, identifiers don't do anything – it's their resolvers that do or don't support these features. For example, suffix passthrough is a feature supported by n2t.net and purl.org ("partial redirect"), but not by doi.org or handle.net.
By metadata flexibility is meant the ability to store any metadata you want, including repeated elements, such as multiple authors and forwarding URLs, or no metadata at all. N2T has full metadata flexibility, while Crossref and DataCite have specific requirements (eg, the DataCite schema) to create their DOIs.
Content negotiation is a way for software to request descriptions of things that are not already in formats that might represent descriptions. Fortunately, to request descriptions without restriction, both humans and software can use inflections, exemplified by the '?' in the first answer. Backed by the right metadata, N2T is one of the few that does both.
What exactly is N2T (n2t.net)?
N2T.net is a resolver originally built for ARKs. N2T stands for Name-to-Thing because strong values of openness prevented it from becoming just another DOI/Handle/PURL-type silo. As a result, the "global ARK resolver" also resolves DOIs, Handles, PURLs, and URNs, along with 600 other kinds of identifier.
This counter-silo principle is also found in micro-service tools such as noid, which was built for ARKs but is routinely used by organizations that mint ARKs and those that mint Handles.
I've heard of ORCIDs and UUIDs – where do they fit in?
Those are special kinds of persistent identifiers. ORCIDs identify researchers, and they link to research works using ARKs, DOIs, etc. ORCIDs look like
https://orcid.org/0000-0001-7604-8041
UUIDs are globally unique, 37-character strings that are easy for software to generate but only become usable as web addresses when made part of a URL, for example, in this ARK:
https://n2t.net/ark:/65665/3c2e39526-e0c3-41ae-be4f-07558a9458eb
