ΦDEVS: phase based discrete event modeling

Even though DEVS provides a convenient framework for discrete event modeling, it can be observed that there is a large difference between the abstraction levels of conceptual models and their specifications in DEVS. Equation based modeling is a declarative modeling style that has become popular for describing continuous dynamic systems in a way that is conceptually closer to conceptual models. Although equation based modeling languages usually include the notion of a discrete event, they are not a natural choice for discrete event modeling. This paper combines equation based modeling with constraint solving in order to create a fully equation based discrete event modeling style. The approach centers around phases, which are described by a constraint (an inequality) and behavior (a set of equations). The resulting models are fully compliant with DEVS: phase descriptions are transformed to internal transitions and time advance. The main contribution of this paper is the adoption of constraints and relations as the sole mechanism to specify models and using an algebraic solver to infer transitions and time advance. Compared to equation based systems, the contribution is to make constraint inequations first-class citizens and to use them symbolically to determine events.