MOON is a notation for designing complete systems, addressing the description of subsystems to be executed by both computer and non-computer processors. The design method is object-oriented in approach, based primarily on the Mascot 3 notation and also on the JSP notation. Systems and subsystems are defined as collections of data repositories, related activities and subsystems. It should therefore also be considered as a modular notation. MOON abstracts a system to a hierarchy of networks of activities and data repositories, using an extension of the Mascot 3 notation. A further development of the system uses a more data-oriented approach, describing actions and data items separately using an extension of the JSP notation. The extensions to the two notations ensure that consistency between network and program abstractions can be enforced.