Cameo Simulation Toolkit comes with an interaction engine that can simulate an interaction element based on the UML semantics. An interaction is a unit of Behavior that focuses on information exchange among internal properties of a Class. You can use it to describe the main Behavior of the Class by specifying the interaction as a Classifier Behavior of the Class. You can also assign it to be a method of an operation of the Class. If an interaction is a Classifier Behavior, it will be simulated whenever the object is started. If it is a method of an operation, it will be simulated when the operation is called.