Representing dynamic structure hybrid models in CAOSTALK

The ability to change model structure during simulation runtime is a key aspect to capture the dynamic nature of many complex systems. We present the Heterogeneous Flow System Specification (HFSS) a modeling formalism designed to describe hierarchical dynamic structure hybrid systems. HFSS is a unification formalism that can model sampled-based and discrete event systems. We show that adaptive step-size numerical explicit solvers for differential equations can be described as sampled systems, making possible to represent hybrid systems in the formalism. HFSS network models can change their composition and interconnection in runtime providing the structural similarity required for representing self-adaptive systems. The CAOSTALK Modeling and Simulation (M&S) environment, an implementation of the formalism in the Smalltalk language is described. We illustrate the use of HFSS by representing a pursuer-target system in CAOSTALK.