Ports and Parts [From the Editor]

Control is the science of interconnection and the technology of integration and informed interaction. What this means is that components have meaning and value only when they are interconnected and communicate with other components through the transmission of energy, material, or information. Whether this interaction occurs through inputs and outputs or—as Jan Willems has shown—through ports and terminals, interaction can give rise to subtle and complex behavior. You and your car are complex amalgams of interacting parts. For engineering purposes, interaction is about integration—ensuring that the parts work together to make a functioning whole. When one or more parts can compute, reason, or think, interaction involves informed action. Together, these phenomena are what control is about.