RULE-BASED SPECIFICATION OF ATOMIC-MODELS

This chapter discusses that the discrete event system specification (DEVS) formalism expressed in the atomic-models class of DEVS-Scheme serves as a basis on which higher level formalisms can be implemented. A convenient rule-based programming style is supported by forward-models, a specialized class of atomic-models. Forward-models are based on a forward chaining paradigm. This is one of many alternatives that are implemented for writing models in a rule-based manner. The chapter discusses that to develop a model of forward-models type, rules are written, which together specify the internal transition, external transition, and output functions of a DEVS model. The ability to write models using rules provides an additional level of decomposition or granularity to model specification. Atomic-models could share such functions but they could not share smaller parts of them. Rules, as more granular knowledge units, make it possible to mix and match specifications among models. As a specialization of atomic-models, the class forward-models generate model objects, which inherit all the instance variables and methods of atomic-models. The state-variables of forward-models are specified in the instance variable ind-vars. They include int-activities and ext-activities that contain lists of internal and external activities.