R4

R4 / 1:Mc

System monitored behavior is performed by zero, one or many Actor

Actor is a monitored behavioral element in exactly one System

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We are interested in the subset of behavioral elements within a System that interact in terms of input or output with the debugger. Consider three instances of the cabin class in the Elevator Case Study. Each is running its own state machine, but our scenario may be focused on the activity of only one of these instances, Cabin<S1> let's say. (the cabin in shaft 1)

We would then designate this instance as an Actor with an address like EVMAN:Cabin<S1>. The other two instances, while possibly active, are not Actor's as far as the debugger is concerned since they don't participate in the running Scenario.

If we are just poking around without a Scenario or we haven't even started interacting, there might not be any Actors. Otherwise there are likely to be at least one per Interaction since an Interaction must have a source R5.