State diagrams. Master system behaviour.

Master system behaviour with state diagrams

What is a state diagram?

A state diagram is the graphical representation of a state machine and one of the 14 UML diagram types for software and systems. State diagrams show a behavioural model consisting of states, state transitions and actions. UML state diagrams are based on the concept of state diagrams by David Harel. State diagrams depict the permitted states and transitions as well as the events that effect these transitions.

What are state diagrams for?

State diagrams are commonly used in the area of embedded systems. State diagrams help to visualize the entire life cycle of objects and thus help to provide a better understanding of state-based systems. An example of such a state-based system is a cash machine: Upon activation either the state ready or the state malfunction could be reached. As soon as the debit card is inserted it is verified. Depending on the result of the verification the pin number is requested or the process is aborted. Other possible states are account query or availablility check etc.