title: How do you go from high level to low level use case diagram?
body: <p>I need to create use case diagrams for a small game.  I have created what I think is a correct, high-level use case diagram.  I now want to create sub-diagrams.  Take "Play Game" for example, there are many actions involved in playing the game, like moving or jumping, so would "Play Game" become the system (box) in the sub-diagram?  I am not quite sure the proper way to expand use cases is.</p>
  
  <p><a href="https://i.stack.imgur.com/sHBQs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sHBQs.png" alt="High Level Diagram"></a></p>