It is represented by a rectangle divided into two sections. The top section contains the trigger , which is the event or condition that activates the transition. The bottom section contains the action , which may cause events, create, destroy, and observe objects and relationships, and send and receive messages. Initial transitions activate initial states, which are the states exhibited by an object when it comes into existence in a system. They have no prior states and are always enabled.
Final transitions are transitions with no subsequent states.
When a final transition fires, the prior states of the final transition are turned off. Exceptions An exception is an event or condition that is not part of normal system behavior. A state exception is represented in the state-net by a bar across a transition arrow. A transition exception is represented by an arrow from the transition in which the exception may occur to a state that the object enters following the exception. Threads An object can be in more than one state at the same time.