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 you to a dissertation, and adding a '?' on the end of the ARK should get 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,
appears inside 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 was once said to be 44 days. At the end of its life, a URL link breaks, meaning it gives you the dreaded "404 Not Found" error. Irritating as that is – and we've all seen it – it's a disaster for libraries, archives, museums, and other memory organizations.
A persistent identifier (sometimes abbreviated PID) is a link that in principle keeps working far into the future, even as things move between websites. Normally when things move, everyone who ever recorded the old links would need to be told what the new links are, which is next to impossible. That's where identifier resolvers come in.
What's a resolver?
A resolver is a website that specializes in forwarding incoming identifiers (the ones originally advertised to users) to whichever websites are currently best able to deal with them. Overall, forwarding is called resolution; one step in a resolution process is called redirection.
For a resolver to work, its hostname must be carefully chosen so won't ever need to be changed. Memory organizations, some of them centuries old, tend to have hostnames well-suited to be resolvers. Some well-known, younger resolvers are n2t.net, identifiers.org, doi.org, handle.net, and purl.org.
How do the ARKs differ from identifiers like DOIs, Handles, PURLs, and URNs?
The short answer as that these are all major types of persistent identifiers, and 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.
That's not to say that making ARKs persistent is cost-free. Keeping any identifiers persistent burdens every 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 you are not charged separately for your identifiers and you are not locked in to a special-purpose resolution silo that also locks out other identifiers.
Is there a longer answer?
Yes, but first let's dispense with what ARKs, DOIs, Handles, PURLs, and URNs have in common. As seen in these examples, they have similar structure:
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
They all start with the protocol (https://) plus a hostname, followed by the Name Assigning Authority (99999, 10.99999, or purl.org), which is the organization that created a particular identifier. Finally there's the name, or local identifier, that it assigned (12345). More things these identifier types have in common:
- They all fail to stop the major causes of broken links: loss of funding, natural disaster, war, deliberate removal, human error, and provider neglect.
- They all burden the end provider with the responsibility to update forwarding tables as URLs change.
- They all give access to any kind of thing, whether digital, physical, abstract, person, group, etc.
- They all identify content that is subject to change on future visits.
- They all break regularly and in large numbers (thousands and more).
- They all use very simple redirection built in to every web server since 1995 and provided for free by hundreds of URL shortening services.
- They all (as a result) leave you wondering if you need them at all, and if so, at what cost.
So how do these identifiers differ? Here's a short list.
- When (not if, because all things pass) the https:// protocol and the hostname cease to exist, only ARKs and URNs indicate 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.
- Although you can use your own or a vendor resolver for your ARKs and URNs, all ARKs can be resolved via n2t.net, making it the closest thing to a "global ARK resolver".
- For URNs there is no single global resolver. In order to register to create URNs, you must apply for a URN namespace.
When should I use ARKs compared to DOIs, Handles, PURLs, and URNs?
There is nothing inherent in ARKs, DOIs, Handles, PURLs, or URNs that make them more or less suitable to identify any kind of thing in any field, domain, or sector. In that sense they are all equally suitable.
Where they differ are in the nature of services and sociology and buzz. xxx
any of these identifier 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 newer kinds of DOIs, such as those from DataCite and EIDR, are changing the nature of the DOI.
XXX
Don't identifier types 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
