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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 metadata, an ARK that comes in to your server with the '?' inflection should be able to talk about itself.
Anchor servingARKs servingARKs
How do I make server content addressable with ARKs?
| servingARKs | |
| servingARKs |
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?
ARKs meant for external use are generally advertised (released, published, disseminated) as actionable identifiers, in other words, as ARKs inside URLs. 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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What are the parts of an ARK?
Core Immutable Identity
_______________|_______________
/ \
Resolver Service Base Object Name Qualifier
_________|________ ________|_______ ______|______
/ \/ \/ \
https://example.org/ark:12025/654xz321/s3/f8.05v.tiff
\_________/ \__/\___/ \______/\____/\_______/
| | | | | |
| Label | | Sub-parts Variants
| | |
Name Mapping Authority (NMA) | Assigned Name
|
Name Assigning Authority Number (NAAN)
What are the parts of an ARK?
| Code Block | ||
|---|---|---|
| ||
Core Immutable Identity
_______________|_______________
/ \
Resolver Service Base Object Name Qualifier
_________|________ ________|_______ ______|______
/ \/ \/ \
https://example.org/ark:12025/654xz321/s3/f8.05v.tiff
\_________/ \__/\___/ \______/\____/\_______/
| | | | | |
| Label | | Sub-parts Variants
| | |
Name Mapping Authority (NMA) | Assigned Name
|
Name Assigning Authority Number (NAAN) |
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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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