The interconnections of subsystems are structurally decomposed and the stability of the overall large-scale system is then investigated, based on these decompositions. With these formulations, the decentralized control design for the interconnected subsystems can be treated as an algebraic problem. The architecture is then extended to solve the decentralized estimation and stabilization problem. The emphasis here is to propose a new method for the qualitative analysis and design of large-scale systems. The advantage lies in its feasibility for a computer-aided control system design (CACSD) set-up.