67. Modeling and Design

The Ptolemy project studies heterogeneous modeling, simulation, and design of concurrent systems. The focus is on embedded systems, particularly those that mix technologies, including for example analog and digital electronics, hardware and software, and electronics and mechanical devices (including MEMS, microelectromechanical systems).

The focus is also on systems that are complex in the sense that they mix widely different operations, such as signal processing, feedback control, sequential decision making, and user interfaces. Modeling is the act of representing a system or subsystem formally. A model might be mathematical, in which case it can be viewed as a set of assertions about properties of the system such as its functionality or physical dimensions.

A model can also be constructive, in which case it defines a computational procedure that mimics a set of properties of the system. Constructive models are often used to describe behavior of a system in response to stimulus from outside the system. Constructive models are also called executable models. Design is the act of defining a system or subsystem.

Usually this involves defining one or more models of the system and refining the models until the desired functionality is obtained within a set of constraints. Design and modeling are obviously closely coupled. In some circumstances, models may be immutable, in the sense that they describe subsystems, constraints, or behaviors that are externally imposed on a design. For instance, they may describe a mechanical system that is not under design, but must be controlled by an electronic system that is under design.