John M. Green
The concept of black boxes has been around since the early days of systems theory though some attribute the first use of the concept to the field of electrical engineering. Regardless, it is a simple concept described by a straightforward definition: if the inputs to a system are known as well as its subsequent outputs but the internal workings of the system are not visible to an outside observer it is a “black box.” In the realm of systems engineering, the application of the black box concept facilitates discussing a system abstractly with a focus on interfaces rather than the details of how inputs are transformed into outputs. However, despite frequent mention in the literature, there is little written about black box theory beyond the basic usage as an abstract or simple system representation. It is reasonable to say that it is not well understood that black box theory can be extended beyond this basic definition.
This paper presents an expanded view of black box theory and how it can be used, especially in model-based systems engineering. It addresses the following questions: how extensible and scalable is black box theory? In what domains and under what conditions is black box theory valid? When is it not valid? What are its limitations? How can it be improved? How is it used with other theories in a complementary way? It also presents a review of selected key system concepts that provide a framework for extending black box theory to diverse applications such functional analysis and performance analysis.