4. State Machine Diagram

4.1. Procedure & Checklist

Brainstorming

Create a table with the following columns:

• 1st column: All states,

• 2nd column: All events that can occur internally or externally,

• 3rd column: All processing steps that must be listed.

Which states does the automat receive?

• The starting point is the initial state.

• By which events is a state left?

• Which subsequent states occur?

• By what is the state defined (attribute values, object relations)?

Does the state machine need a final state?

• If the final state is reached, the processing of the state machine ends.

• If the state machine describes a life cycle, the termination of the state machine can be equated with the end of life of the object.

• No processing may be performed in a final state; it may not have any output arrows.

Which activities are to be modeled?

• Is there any processing associated with a state diagram?

• Do all incoming transitions of a state have the same activity? –> entry activity

• Do all outgoing transitions of a state possess the same activity? –> exit activity

• Is the processing linked to the duration of the state? –> do-activity

Which events are to be modeled?

• External events from the user or from other objects;

• Temporal events (duration, time);

• Internally generated events of the class or use case.

Analytical steps - Appropriate state name.

• Describes a specific time period.

• Does not contain a verb.

Analytical steps - Are all transitions correctly entered?

• Is every state reachable?

• Can each state - except the final state - be exited?

• Are the events of the transition unique?

• Can events occur that are not covered by the specified events?

Source: “UML 2 compact with checklists”, Heide Balzert

4.2. Further

Hint

State diagrams can be created online on draw.io (https://app.diagrams.net/).

Note

In the literature there are different uses of the “entry”, “do” and “exit” conditions. We use the following notatin:

• Entry activity: action which is triggered when entering the state, e.g. light = False

• Do activity: action which is executed as long as you are in this state, e.g. count sheep

• Exit activity: action which is executed when one leaves the state, e.g. sleep = True

https://www.visual-paradigm.com/guide/uml-unified-modeling-language/what-is-state-machine-diagram/

4.3. Examples for state diagrams

Example for the circuit of a person traffic light