Symbolic Discrete-event Simulation *

The event-scheduling view of the discrete-event simulation technique is widely used to model and simulate dynamic systems. This paper presents DMOD, a formalization of this technique. It ooers two main advantages. First, it retains the powerful intuitions behind this technique yet makes it easier to use them. In particular, it proposes a new method for logically specifying event preemption. Second, DMOD permits temporal reasoning about modeled systems. This is done by means of symbolic simulation, i.e. simulation in which input parameters can be constrained variables. Symbolic simulation yields histories parame-terized by input variables. Simple manipulation of symbolic histories allows proof of a range of temporal properties such as safety, possibility, or sensitivity. Restrictions upon models are outlined which allow symbolic simulation to proceed eeciently. DMOD is illustrated by means of a hybrid system, a railroad crossing with continuous, non-linear state and discrete events. DMOD has been implemented in Prolog and CLP(R) and applied to analysis of a variety of industrial systems.