Some application works with geometric primitives. They are circles, squares etc. User can change positions of such primitives, also he can copy/delete/select them. Where should intermediate data be stored in mvc? Some kind of intermediate data in such case are (for example) selected primitives. As I understand it is not model data. They are data which represent state of View. But what about notifications about changing selection? I suppose that Controller should keep this data and notify listeners about appropiate changes of selection. But in my understanding of mvc, Controller should not know about view