A modular design for an automation system is essential for Lean Validation during the project phase, but even more during the operation phase of a system. For Manufacturing Execution Systems (MES) systems the ISA-95 standard helps to make the system modular; for Process Control Systems (DCS) the ISA-88 standard is essential.

A modular design has two major advantages:

• When creating independent modules it is easy to modify one module without modifying other modules in the system.
• Objects with the same functionality can use the same code. When this object is tested once, instances of this code do not have to be tested all over.