State Machine

idle -> loading -> success/error, error -> retrying -> success/error

Authentication

logged-out -> authenticating -> logged-in -> logging-out -> logged-out

Multi-Step Wizard

step1 -> step2 -> step3 -> review -> submitting -> complete

Modeling Approach

1. List all possible states
2. List all events/triggers
3. Define valid transitions
4. Identify impossible states to prevent
5. Add guards for conditional transitions
6. Define entry/exit actions per state

Benefits

• Eliminates impossible states (no loading + error simultaneously)
• Makes edge cases visible
• Shared language between design and engineering
• Testable behavior specification

Best Practices

• Start with the happy path, then add error states
• Every state should have a way out (no dead ends)
• Keep state machines focused (one per concern)
• Document with visual diagrams
• Map each state to a UI representation