Definition

Typically, identifiers are used to connect content in resources to external content available in other frameworks or protocols.

Type

identifier

Key	Type	Cardinality	Description
system	uri	0..1	Establishes the namespace for the value - that is, a URL that describes a set values that are unique.
value	symbol	0..1	The portion of the identifier typically relevant to the user and which is unique within the context of the system.
use	code	0..1	The purpose of this identifier. Proposed values are: `usual`: The identifier recommended for display and use in real-world interactions which should be used when such identifier is different from the "official" identifier. `official`: The identifier considered to be most trusted for the identification of this item. Sometimes also known as "primary" and "main". The determination of "official" is subjective and implementation guides often provide additional guidelines for use. `temp`: A temporary identifier. `secondary`: An identifier that was assigned in secondary use - it serves to identify the object in a relative context, but cannot be consistently assigned to the same object again in a different context. `old`: The identifier id no longer considered valid, but may be relevant for search purposes. E.g. Changes to identifier schemes, account merges, etc.
period	period	0..1	Time period when identifier was/is in use.

{
  "system": "<uri>",
  "value": "<symbol>",
  "use": "<code>",
  "period": { Period }
}