Glossary · Systems engineering and MBSE
State machine diagram
Also known as: State diagram, Statechart
German: Zustandsdiagramm
In SysML and UML, a state machine diagram is a behavior diagram that shows the states of an element, the events and conditions that trigger transitions between them, and the actions performed on entry, exit or during a state.
- Systems engineering
In one sentence
A state machine diagram shows the states of an element and the events that trigger transitions between them.
Example
The state machine of a filling machine shows 'Idle', 'Running', 'Held', 'Stopped' and 'Fault', with an acknowledged reset required to leave 'Fault'.
How it applies
- Engineering: Operating modes, machine states and fault handling are naturally modeled as state machines; PackML-style state models are a common example.
- Safety: State machines help verify that every fault leads to a Safe state and that restart needs a deliberate action.
- Documentation: Mode and state descriptions in the operating manual should match the modeled states and transitions; the documentation team can use the diagram to check completeness.
- Testing: Each transition is a test case; checking that invalid transitions are rejected is as important as checking the valid ones.
State machine diagram vs. state model
A State model is the concept of states and transitions of a system; the state machine diagram is the SysML notation used to express it.