Base StructureDefinition for Identifier Type: An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.

Identifier
use
usual | official | temp | secondary | old (If known)
type
Description of identifier
system
The namespace for the identifier value
value
The value that is unique
period
Time period when id is/was valid for use
assigner
Organization that issued id (may be just text)