An ISA88 Phase in IEC 61131-3 code based on the concepts of a Normalized flow element

Evolvability is one of the most desirable non-functional requirements of software architectures. In the area of automation control, the permanent shift of the requirements and the prevention of side-effects are key points. In addition, adaptability and flexibility in manufacturing systems continue to gain importance. This paper proposes an approach to achieve evolvability in IEC 61131-3 based software modules, from a structural point of view, i.e., starting from an individual line of code. We based our design of an evolvable ISA88 Equipment Phase on the Normalized Systems theory recently introduced. It seems indeed possible to develop evolvable IEC 61131-3 based modules with the existing, commercially available development environments. However, our guidelines require a disciplined programming style in extending software, based on a limited set of anticipated changes.