Re-usable software design for programmable logic controllers

Abstract

It is the aim of this paper to present a model conceived for supporting the initial, critical phases of PLC software life cycle, namely requirement specification, requirement analysis and software design, to obtain reusable code. The model, named EASIER, is based on an object-oriented paradigm where the message-method mechanism is replaced by the law and action primitives, since they are more suitable to cope with the real-time, cyclic nature of PLC software. Software re-usability is pursued by identifying independent control modules through a proper bedded encapsulation mechanism, representing system dynamics by means of synchronized state diagrams, expressing context-free behaviour of system components by introducing virtual objects. The EASIER approach is presently validated with respect to relevant reverse and forward engineering applications; from one of these cases we derive the examples used in the paper.