In supervisory control of discrete event dynamic systems, the idea of decentralized control is employed for the flexibility and the reduced complexity in the supervisor synthesis. To extend this approach, we consider the problem of compatible combination of decentralized with centralized control in case pure decentralized control becomes inadequate. We introduce the concepts of locally controllable pair and its candidate along with some deriving conditions. Then several fundamental theorems are presented and an analytical framework for mixed centralized/decentralized supervisory control systems is proposed based upon the theorems.