Modelica Extensions for Supporting Message Passing Communication and Dynamic Data Structures

Discrete-event modeling methodologies, such as DEVS, Parallel DEVS or the process-oriented approach used by Arena, support the description of systems in a modular and hierarchical fashion. In these approaches, model components communicate by means of message interchange. Messages constitute impulses of information instantaneously sent from one component to another, either individually or arranged in groups, or bags. Dynamic data structures are required to manage bags of messages, either locally or as inputs/outputs of components. This communication approach is conceptually different from the connection between components used in the physical modeling approach supported by Modelica. Improving Modelica to support message passing communication facilitates the description of DEVS models and the development of libraries with analogous functionality to Arena. The authors have previously implemented message passing communication in Modelica using external C functions, but these implementations present some restrictions. The concepts required to describe message passing communication in Modelica are discussed, and a proposal to extend the language is presented. Two simple application examples are also included to illustrate the use of the proposed extensions.