Statecharts

Finite State Machine

A mathematical model of computation. An abstract FSM can be in one of the finite number of states at a given point of time.

• State: A status of the system.
• Transition: A change from one state to another. Based on input events.

Statechart Diagram

Described temporal evolution of an object of a given class in reponse to interactions with other objects.

Event

One-way communication between 2 objects. Atomic (non-interruptible), asynchronous. May cause a transition.

State

Depicted as a rounded rectangle with upto 3 sections. Might be

• name - optional
• state variables
• triggered operations
• entry event: Occurs when entering the state
• exit event: Occurs when exiting the state

Operation

An atomic action invoked by a transition.

Activity

An ongoing operation that takes place while object is in a given state.