Q:

Understanding UML for MVC

http://www.tutorialspoint.com/design_pattern/mvc_pattern.htm
i don't understand, why the arrow between controller and View/Model are association and not aggregation.
Controller class use Model und View, which was created by Demo, so it  keeps the reference of the objects and therefore it is a aggreation?

A:

In UML, if A is an aggregation of B means that A is composed of B and B ceases to exist if A ceases to exist. 
In MVC, the controller is not composed of the view nor is the life of the view necessarily controlled by the controller - normally they all are contained in a framework.
Of course, you can use the MVC pattern and make the controller the owner of the view ( or the other way round ), but that is not essential to the pattern. 
Although many languages run in garbage collected environments so the lifecycle aspect isn't really relevant to them, you still can use the association/composition/aggregation hierarchy to show the intended relationship and whether the parts have a meaning outside of the whole. 

