Sequence Diagram

Sequence of message sent between set of objects to perform a task

• The vertical line is called lifeline
• The vertical box is called activation box

Most diagrams follow this "Cheat Sheet" pattern:

1. Actor → Boundary: "Click Button".

2. Boundary → Controller: "Process Request."

3. Controller → Controller: "Self-compute" (The loop-back arrow).

4. Controller → Database: "Save/Fetch Data."

5. Return Message: Dashed line (←−−) back to the Actor.

6. alt: Use for "If/Else" (e.g., If login succeeds vs. fails).

7. opt: Use for Optional steps (similar to the «extend» relationship).

8. loop: Use for "Repeating" actions (e.g., "Wait for connection").

Using Frames