I have an existing textual model to which I would like to add some diagram views.  It was straight-forward to add an icon to a class.  When I opened the diagram view on a second class that contained an instance of the first class, I expected to see an icon show up, but it didn't.  Before I just start drawing diagrams on top of an existing text model, can someone give me a tip or two to help get me started in the right direction of adding graphics to an existing textual model?  I want to do this in a way that adds only annotations without making any changes to the definition of the model itself.