A Rationale for Both Nesting and Inheritance in Object-Oriented Design

It has been observed that design of complex objects such as software requires both decomposition by form (atomic objects) and decomposition by function (nesting) in order to reduce the design to a set of manageable components. However, the object-oriented design paradigm mostly supports decomposition by form. This paper uses a simple example to motivate the need for nesting (decomposition by function) and illustrates how nesting might be incorporated into a design language. We then demonstrate how the introduction of nesting into software specification and design significantly increases reusability. AD-Vcharts, a new visual formalism, and VDM are used to provide a semantics for nesting.