Problem wording :
Design a system enabling to display on a screen some empty windows (no button, no menu...). A window can have several different styles depending on the platform used. We consider two platforms, XWindow and PresentationManager. The client code must be written independently and without knowledge of the future execution platform. It is probable that the system evolves in order to display specialized windows by “application windows” (able to manage applications) and “iconised windows” (with an icon).