System complexity measure in the aspect of operational difficulty

The complexity of a system arises not only due to the number of components and the characteristics of each component, but also to the types of interconnections between the components. A method of measuring this structural complexity is suggested as reflected in system operational difficulty using an information theoretic approach. This method, the functional entropy measure, can denote the structural complexity induced from the interconnections between components. An equation for calculating the diagnostic entropy without introducing any approximation is derived. The role of monitoring instruments is also studied, and the results show that the monitoring of a system not only can reduce, but also can increase the entropy of the system. To know the true condition of a monitored system with far greater confidence than if it remains unmonitored, the monitoring instrument must be much more reliable than the monitored component