Interpreting a Sequence Diagram

• Each key press results in separate call to dial, but only one is shown
  
• Connection wants to get greeting to play
• Each mailbox knows its greeting
  
• Connection must find mailbox object:
  Call findMailbox on MailSystem object
• Parameters are not displayed (e.g. mailbox number)
• Return values are not displayed (e.g. found mailbox)
• Note that connection holds on to that mailbox over multiple calls