title: Data modeling diagram notation, what is this?
body: <p>What does this type of notation mean in a logical data model? There is three tables in this diagram and x inside "half moon". So, what is this "x inside half moon". I could not find this e.g. from different diagramming conventions mentioned in <a href="http://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model" rel="nofollow">Wikipedia</a>.</p>
  
  <pre><code>             _________
              |_________|
              |         |
              |_________|
                   |
                   |  
                 -----
                /__x__\
                   |
            _______|_________
      _____|_____        ____|______
     |___________|      |___________|
     |           |      |           |
     |           |      |           |
     |___________|      |___________|
  </code></pre>