Alternative identity for a focus.

Item Summary
Name	Type	Multiplicity	Description
source	container FocusIdentitySourceType	[0,1]	Source of the identity data.
data	container FocusType	[0,1]	The data itself.

Items
- source
  
  Flags: RAM,runtime
  
  Multiplicity: [0,1]
  
  Source of the identity data. Conceptually similar to `ProvenanceAcquisitionType`, but there are some small differences: we are not interested in the timestamp (yet), and we keep more detailed information for resource objects.
- data
  
  Flags: elaborate,RAM,runtime
  
  Multiplicity: [0,1]
  
  The data itself.