title: To get primary and foreign keys right in ERD
body: <p>I read my notes and I am now unsure about the keys.</p>
  
  <p><strong>My logical diagram</strong></p>
  
  <p><a href="http://files.getdropbox.com/u/175564/db/db-11.png" rel="nofollow noreferrer">alt text http://files.getdropbox.com/u/175564/db/db-11.png</a></p>
  
  <p>This table should be in line with the following physical ERD</p>
  
  <p><a href="http://files.getdropbox.com/u/175564/db/db-22.png" rel="nofollow noreferrer">alt text http://files.getdropbox.com/u/175564/db/db-22.png</a></p>
  
  <p>I have only one foreign key in the table <code>Question</code>.</p>
  
  <p>I would like to know </p>
  
  <ul>
  <li>should the <code>question-id</code> and <code>question-tag</code> in the table <em>Question-tag-xref</em>, AND <code>question-id</code> and <code>answer</code> in the table <em>Answers</em> be also foreign keys?</li>
  </ul>