title: UML aggregation vs association
body: <p>Here I am, with another question about aggregation and association. I wanted to learn some basics of UML, so I started reading "UML distilled" by Martin Fowler. I read both chapters about classes, and there is one thing that I can't fully grasp I think, and that is aggregation vs association. In the book there is this quote:</p>
  
  <blockquote>
    <p>In the pre-UML days, people were usually rather vague on what was aggregation and what was
    association. Whether vague or not, they were always inconsistent with everyone else. As a result,
    many modelers think that aggregation is important, although for different reasons. So  the UML
    included aggregation (Figure 5.3) but with hardly any semantics. As Jim Rumbaugh says, "Think of it
    as a modeling placebo" <em>[Rumbaugh, UML Reference].</em></p>
  </blockquote>
  
  <p>As I understand from this quote and topics that I read on Stack Overflow it doesn't matter which one of those two relations I use, they mean basically the same, or is there any situation where the usage of aggregation instead of association would be justified and/or I could not change one to the other without changing the "meaning" of a class diagram?</p>
  
  <p>I am asking this, because this book is from 2003 and some things could have changed during those few years.</p>