The openEHR reference model currently does not have a
type which can be used for identifying real-world entities (RWEs)
such as prescriptions, lab orders, specimens, people (e.g. by
social security number or medicare card number) etc. In addition,
such identifiers should be a subtype of DATA_VALUE, enabling their
use in archetyped structures based on ITEM_STRUCTURE / CLUSTER /
ELEMENT.