This transaction informs the recipient that there has been a change to the link between a “local patient ID” and its corresponding XAD-PID.
It should not to be confused with the similar link/unlink events documented in transaction ITI-30 (Patient Identity Management) which is used by patient demographic suppliers to notify other interested systems about changes to its own local patient identity records. 
The transaction can be used in any setting where it is appropriate to have XAD-PID link changes processed as a single event, rather than require individual metadata updates to each object.
