The SHIFT Programming Language for Dynamic Networks of Hybrid Automata

SHIFT is a programming language for describing and simulating dynamic networks of hybrid automata. Such systems consist of components which can be created, interconnected and destroyed as the system evolves. Components exhibit hybrid behavior: continuous-time phases separated by instantaneous discrete-event transitions. Components may evolve independently, or they may interact through selected state variables and events. The interaction network itself may evolve. The SHIFT model and language were motivated by our need for tools that support dynamically reconfigurable hybrid systems. Our primary application is the specification and analysis of different designs for automatic control of vehicles and highway systems [19]. We need to capture the behavior of vehicles, sensors, actuators, communication devices and controllers in a structured and modular specification [4]. Models for these components are provided by different groups of experts and then integrated in different ways for comparative analysis. From our previous experience in modeling [10, 6], analysis [17, 3] and implementation [5, 7], we adopted the hybrid systems approach for modeling the system components. Since spatial relationships between vehicles change as they move, our application is characterized by a dynamically changing network of interactions between system components. SHIFT has since also been used in coordinated autonomous submarines [18], air traffic control systems [11], and material handling systems. In the rest of this section, we examine other work related to the SHIFT approach. In section 2, we describe the main features of the SHIFT language—states, inputs, outputs, differential equations and algebraic