title: Different relationship between 2 entities
body: <p>In my project I have a part where says -</p>
  
  <blockquote>
    <p>An <strong>airline</strong> has many <strong>flights</strong>
    and each flight has one <strong>source (airport)</strong> and one or more <strong>destinations (airports)</strong>. For each source destination pairs, you have to record the <strong><em>distance</em></strong>.</p>
  </blockquote>
  
  <p>According to this statement I have done an erd like this -</p>
  
  <pre><code>                   _________
                    | Airline |
                     ---------
                         |
                        has
                     ____|____ 
                    | Flights |
                     ---------
                 /               \
              s.has             d.has
        _______/______       ______\_______
       |source_airport|     | dest_airport |
        --------------       --------------
  </code></pre>
  
  <ul>
  <li><p>Now I am having problem with the last attribute <strong><em>distance</em></strong>. How should I place it with the above erd?</p></li>
  <li><p>Alternately I am thinking the <strong>Airport</strong> will be a single entity where <strong>Flights</strong> &amp; <strong>Airport</strong> will have a relationship between them. But if this happens how to distinguish the <strong><em>source</em></strong> and <strong><em>destination</em></strong> part between them as well as solve the problem with <strong><em>distance</em></strong> attribute?</p></li>
  </ul>