title: How to represent submodules in use case diagram
body: <p>I need to know, how to represent the sub modules of a module.</p>
  
  <p>For example i am having a module called X. This module X is actually made up of three sub modules called x1, x2 and x3. User can choose any of this sub module from the available options. That means this module does not exits with out this 3 sub modules. My doubt is that while drawing the use case diagram how can i represent this sub modules? I have to use "include" or "extend" for this sub modules from the main module?</p>
  
  <p>Another doubt is that when i am drawing the use case diagram of x1. How can I represent a main work called "view location" and an optional work called "change map view"</p>
  
  <p>Kindly explain the answer.</p>