We introduce a theory for the identification, modeling, and formalization of two methodologically essential, complementary views onto software and software intensive systems. One view addresses mainly tasks in requirements engineering when describing the overall system functionality from the users? point of view. By this view we aim at the specification of the comp rehensive user functionalities of multi-functional systems in terms of their functions, features, and services as well as their mutual dependencies. This view leads to a function or service hierarchy. The other view essentially addresses the design phase with its task to develop logical ar chitectures formed by networks of cooperating compone nts that are specified by their interface behavior.