7. Sequence Diagram Essentials, Cont.

• Typical sequence diagram captures the behavior of a single scenario.

• Thus, sequence diagram shows possible implementation of one scenario.

• Sequence diagrams show the interaction as follows:

  1. Each participant has a lifeline that runs vertically down the page

  2. The ordering of messages sent accross object lifelines is interpreted by reading down the page.

  3. Each lifeline has an activation bar that shows when the participant is active in the interaction.

  4. Return arrows (optional) show values returned from the call.

• In most cases sequence notation is self-explanatory.

• Bottom line: good diagram should be readable by all indended audiences.