We could say that a window is each passage in "Case of Use", or if we preferred it, a set of controls that show a information and receive another one.

A window is formed by a Panel, who is the set of visible controls of the application, a set of Operations (services, methods of business…), a context, that is the mechanism to interchange data between the controls and the operations.
In each window, also we must indicate "navigation", that is to say, we must indicate "to what window we must go" and "with what conditions".
The services appear as options of the bar of tools. Some services are not visible in that bar, because they are accessible through other controls (for example, bellboys in the panels).
Certain bellboys can appear like "not inhibited", because they are hoping that certain condition is fulfilled (for example, that some field fills up).
The windows can also have certain objects (that in java they call "beans") that give a global functionality to the window. For example, we can have as "beans" the connection to the data base (not to have too many), a remote service (that in java calls "Enterprise Java Beans") or any other Java object.

In order to define navigation between windows, first we have the list of "Operations" that are accessible from this window.
Later for each operation we indicated that possible results can have (we called "Option"). If we did not indicate them, or not it produces no of the indicated ones we did not change of window and we followed in the same one.
The mechanism is very simple, the operations, to the being executed, leave in the context a result. This is what it is verified.
When indicating a window name we can indicate "back", so that it returns to previous (losing the data of this one) or "first" so that it goes to the initial window of Caso de Uso.