UML-based Approach for the Re-Engineering of PLC Programs

Re-engineering and reuse of programs implemented on programmable logic controllers (PLCs) became vital in the recent years. This is because the programming of PLC programs is an exhaustive and expensive activity. This paper outlines a re-engineering approach based on the formalization of PLC programs. The approach utilizes XML as an intermediate step for the transformation of the existing PLC programs into a vendor independent format. After this transformation XML is used as a basis for the visualization and formalization of the PLC code. The formalization consists of two main steps: first the modular structure of the program is transferred to an UML class diagram and in the second step the algorithms contained in the modules are converted to state diagrams. This conversion uses an abstraction method to avoid large automata