An identifier that uniquely identifies a thing or object. Examples are object identifier for HL7 RIM objects, medical record number, order id, service catalog item id, Vehicle Identification Number (VIN), etc. Instance identifiers are defined based on ISO object identifiers.
If a value is an exceptional value (NULL-value), this specifies in what way and why proper information is missing.
A unique identifier that guarantees the global uniqueness of the instance identifier. The root alone may be the entire instance identifier.
A character string as a unique identifier within the scope of the identifier root.