Systems Engineering

Given an identified need or desire, how does one select the best design to satisfy it out of the infinite number of possible solutions? For a complex project, the concept of a System has proven useful. A System is defined as a functionally, physically, and/or behaviorally related group of regularly interacting or interdependent elements. They are distinguished from the rest of the Universe by a System Boundary (Figure 1.5-1). A system is not a physical entity, but rather a mental construct, created because of its usefulness, by drawing a line or surface around a collection of elements. The elements have internal relationships to each other and form a comprehensible whole. The rest of the Universe outside the system is referred to as the System Environment, or simply the environment. Flows of many types enter and leave the system as Inputs from and Outputs to the environment by crossing the system boundary. The scope of a given engineering task is then defined by the system boundary, what crosses the boundary, and what is inside. Systems may contain smaller systems within them, which are called Subsystems. These may be nested to any level, but flows into and out of a subsystem must appear in the parent system, or at the top level in the environment. This rule may be called Conservation of Flows - that flows do not appear from or vanish into nothing. Following that rule ensures that all the required inputs and outputs are accounted for.