title: ERD vs UML association - erd being constrained more?
body: <p>In an <a href="http://www.tdan.com/view-special-features/8457" rel="nofollow">article</a>
   David C. Hay, I found the following:</p>
  
  <p>In one sense a UML association is equivalent to an entity/relationship relationship, but a </p>
  
  <blockquote>
    <p>relationship in an entity/relationship model is more constrained in
    what it can represent than is an object-oriented association.
    Specifically, as will be described below, each relationship is a pair
    of assertions about the nature of the business. It is not simply
    recognition that two things are somehow associated with each other.</p>
  </blockquote>
  
  <p>But it does not explain (or I do not get it) how is ERD relationship more constraained when compared to UML?</p>