Communication with external domains is both synchronous and asynchronous.
An outgoing asynchronous signal is sent using the
=> symbol like this:
Set destination( Shaft ID : Shaft, Floor name : Destination ) => UI
An incoming asynchronous signal will appear like any event, so no special notation is needed.
An outgoing synchronous call looks like this:
press status = SIO.Above inject pressure()
Incoming synchronous calls will invoke internal domain operations.