title: Ideal example of a Use Case diagram
body: <p>I am looking for an ideal example of a Use Case diagram which would explain most of the tricky places and be a good model for new Use Case diagrams.</p>
  
  <p>It must have following things:</p>
  
  <ul>
  <li>abstract Use Cases</li>
  <li>concrete Use Cases</li>
  <li>"extends" relation</li>
  <li>"include" relation</li>
  <li>"inherits" relation that connects abstract and concrete Use Cases</li>
  <li>at least two concrete actors</li>
  <li>an abstract actor</li>
  </ul>
  
  <p>And of course it should be</p>
  
  <ul>
  <li>syntactically correct (UML 2.x conform) </li>
  <li>semantically correct</li>
  <li>comprehensive</li>
  <li>not too complex</li>
  </ul>
  
  <p>I searched myself and didn't find any good example that would contain all the things.</p>
  
  <p>Probably somebody has such an example and can share it. Thank you in advance!</p>