title: What does a diamond sign signify in UML class diagrams?
body: <p>Consider the below two diagrams. The top one contains a plain arrow at the right end, and the bottom one contains an arrow with a diamond at the left end and a plain arrow at the right end. The <a href="https://rads.stackoverflow.com/amzn/click/com/0201634988" rel="noreferrer" rel="nofollow noreferrer">great book GoF</a> has usages of  both of these two kinds of diagrams. </p>
  
  <p>I want to understand what does the <strong>diamond</strong> signify in the second case, and which one of these two gives a stronger association between <code>Customer</code> and <code>Order</code>. </p>
  
  <p>Is the <code>Customer</code> class responsible for the lifecycle of <code>Order</code> class in either of the two cases?</p>
  
  <p><img src="https://i.stack.imgur.com/sta7R.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/e4SrZ.png" alt="enter image description here"></p>