Elaborate control: variable-structure modeling from an operational perspective

Much effort has been put into the modeling and simulation of variable-structure systems, and there is a consensus on the intuition of viewing a variable-structure model as a hybrid automaton that consists of several modes. Each mode corresponds to a classical static-structure model and events control the transitions between modes. Usually, the number of modes is considered to be finite and small in practice. This assumption conflicts with the composition of models, that easily generates a large number of potential modes. We argue that variable-structure modeling equals a form of explicit control over the process of elaboration and simulation and that this control should be exposed, carefully, to the modeler. This feature allows writing models with a practically unlimited number of modes. We provide a core calculus that defines the language primitives for this task and then integrate elements from that calculus into Modelica, enabling straightforward modeling of variable-structure systems in this established modeling language.