An OPC UA interface for an evolvable ISA88 control module

Normalized systems theory has recently been proposed to engineer evolvable information systems. This theory includes a potential of improvement in control software for the automation of production systems. This paper aims at contributing towards evolvable and therefore easy-to-maintain control software. We introduce IEC 61131-3 code which complies with the theorems of normalized systems, forming a building block which complies with the model of an ISA88 control module, accessible via an OPC UA interface. Since OPC UA brings control software to a new level, it enables original intra-process projects to interoperate in an inter-process context. OPC UA offers new possibilities for system integration, but might also lead to a larger impact of evolvability problems.