title: Push, pull mechanism observer pattern
body: <p>At the moment I'm studying design patterns and I've come to a part where I'm confused whether the observer pattern makes use of the push mechanism or does it make use of the pull mechanism?</p>
  
  <p>I've read different implementations of this and can't really establish which one is correct.</p>
  
  <p>Also, I'd like to know three straight forward advantages of the push model towards the pull model.
  I guess one of them is that the push model is less coupled then the pull model?</p>