For a more complete description, see the Overview of the Ptolemy Project.The Ptolemy project studies modeling, simulation, and design of concurrent, real-time, embedded systems. The focus is on assembly of concurrent components. The key underlying principle in the project is the use of well-defined models of computation that govern the interaction between components. A major problem area being addressed is the use of heterogenous mixtures of models of computation. A software system called Ptolemy II is being constructed in Java.
The class of systems addressed by the project is sometimes called reactive systems. Reactive systems are those that interact with their environment at the speed of the environment. They are often embedded systems, and have been contrasted with interactive systems, which react with the environment at their own speed, and transformational systems, which process a body of input data to produce a body of output data. Reactive systems typically include elements of signal processing, communications, and real-time control. They are typically implemented with mixed technologies, possibly including embedded software, custom digital hardware, configurable hardware, analog circuits, microwave circuits, and microelectromechanical systems (MEMS).
A key principle in the Ptolemy project is the use of multiple models of computation in a hierarchical heterogeneous design environment. A premise in this work is that no single general purpose model of computation is likely to emerge in the near future that will deliver what designers need. Modeling the diverse implementation technologies and their interaction is not reasonable within a homogeneous environment. Consider embedded DSP software controlling a MEMS device, for example. The MEMS device requires physical modeling using differential equations, a modeling technique that is entirely inappropriate for the DSP software. Moreover, the ability to validate designs and to synthesize high-quality implementations from high-level abstract models are both compromised by generality in the modeling framework.
The project aims to develop techniques supporting heterogeneous modeling, including both formal "meta-models" and a software laboratory for experimenting with heterogeneous modeling. In this context, it has explored methods based on dataflow and process networks, discrete-event systems, synchronous/reactive languages, finite-state machines, and communicating sequential processes. It has made contributions ranging from fundamental semantics to synthesis of embedded software and custom hardware.
The approach of the Ptolemy project at this time includes:
Ptolemy software provides the laboratory for the experimental side of the project. It supports the interaction of diverse models of computation by using the object-oriented principles of polymorphism and information hiding. For example, using Ptolemy software, a high-level dataflow model of a signal processing system can be connected to a hardware simulator that in turn may be connected to a discrete-event model of a communication network.
Since the Ptolemy Project began, numerous advances in semantics, design, simulation, and code generation have occurred. Results of the Ptolemy Project have included:
The Ptolemy software environment has been used for a broad range of applications including signal processing, telecommunications, parallel processing, wireless communications, network design, investment management, modeling of optical communication systems, real-time systems, and hardware/software co-design. Ptolemy software has also been used as a laboratory for signal processing and communications courses. Currently Ptolemy software has hundreds of active users at various sites worldwide in industry, academia, and government.