title: SQL - Is Associative entity a weak entity?
body: <p>I am quite confused by the concepts of <a href="http://en.wikipedia.org/wiki/Associative_entity" rel="nofollow">Associative entity</a> and <a href="http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Weak_entity.html" rel="nofollow">weak entity</a>. Is the associative entity a weak entity? If not, is there any relation between these two concepts? just take the following database as an example:</p>
  
  <ul>
  <li>Student(<strong>StudentID</strong>,StudentName,...) </li>
  <li>Enroll(<strong>StudentID*</strong>,<strong>CourseID*</strong>)</li>
  <li><p>Course(<strong>CourseID</strong>,CourseName,...)</p>
  
  <ol>
  <li><p>Is the <code>Enroll</code> an entity? Yes, I think. It is an assoicative
  entity. </p></li>
  <li><p>Is it a weak entity? The definition of weak entity is: a
  Weak Entity is an entity that cannot be uniquely identified by its
  attributes alone; therefore, it must use a foreign key in
  conjunction with its attributes to create a primary key. In this
  case, <code>Enroll</code> doesn't have its attribute ( Am I right?), so
  according to the definition, it should be a weak entity. So is my
  logic right? is the associative entity also a weak entity?</p></li>
  </ol></li>
  </ul>
  
  <p>Thanks!</p>