title: Is database a controller or boundary in a sequence diagram?
body: <p>I am having issues identifying whether the database is a controller or boundary (view) in a sequence diagram.
  I have drawn the following sequence diagram for 'call queueing'. Is it correct?
  <a href="https://i.stack.imgur.com/oEEpU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oEEpU.png" alt="enter image description here" /></a></p>