A flexible decentralized and hierarchical architecture is presented to reduce computational effort in designing optimal nonblocking supervisors for discrete-event systems (DES). We organize a DES into modular subsystems that embody internal interacting dependencies. Verification of, and coordination among modular subsystems are achieved through their model abstractions. Sufficient conditions are presented to guarantee that coordinators and modular supervisors result in maximally permissive and nonblocking control. A medium-sized example demonstrates the computational effectiveness of our approach.