What is a Persistent Identifier?

A Persistent Identifier (PID) is an identifier pointing to a resource with no knowledge of the resource. It is an opaque string with the following structure:

<PREFIX>/<SUFFIX>

The PREFIX identifies a PID by the leading "21." This is followed by an optional "T" (see below) and 5 digits.

The PREFIX identifies a namespace in which the SUFFIX must be unique. Besides this requirement, SUFFIX could be any string not containing slashes.

CSCS manages the prefixes for Swiss organizations starting with 21.17xxx and has an own prefix 21.17101.

A PID should always resolve to an URL. If the corresponding data has been removed, it should resolve to a page that states the data is missing. The PID itself could never be deleted. An example is 21.17101/EPIC_HEALTHCHECK.

CSCS owns also the prefix 21.T17999 used for testing. A test PID can be deleted anytime and normally has associated a TTL (Time To Live) value of one day. An example is the, already expired, 21.T17999/12345-54321 test handle.

If your organization has an own a PID prefix in the Swiss namespace  (21.17xxx and 21.T17xxx). The custom PREFIXs start at 21.17102, with the last three digits going up, or a test one from 21.T17998  with the last three digits counting down.

Next step is to understand the process that resolves a PID into the corresponding URL pointing to the data.