title: UML - Use Case - Identify not registered user and registered users
body: <p>I'm planning to write a service of event handling (like Google's Doodle) and, in the use case diagram, I need to distinguish between registered users and not registered users.
  At first, I thought that:</p>
  <blockquote>
  <p>Registered User _ is generalization of _ Not Registered User</p>
  </blockquote>
  <p>with the following actions:</p>
  <blockquote>
  <p>Not Registered User ---&gt; Registration to the service</p>
  <p>Not Registered User ---&gt; Partecipate to an event</p>
  <p>Registered User ---&gt; Login to the service</p>
  </blockquote>
  <p>But I don't know if I didn't understand the theory behind use cases:
  should I use only one actor (&quot;User&quot;) and associate him all the actions,
  or keep this generalization?</p>