Abstract: Production possibility set (PPS) is the basis for constructing DEA models of network systems. The connection conditions of sub-processes are the key points for building the PPS. In nature, the existing network DEA models assume that all inputs and outputs of sub-processes satisfy the strongly free disposability principle. However, it is not always true in real production and management activities. Therefore, from the perspective of different free disposability principles, the connection conditions for inputs and outputs of sub-processes are studied; the production possibility sets and their equivalent formulations for general network systems are built. The DEA models are constructed accordingly for evaluating the efficiencies of network systems are built. In the end, the proposed models are used to evaluate the performance of China's listed banks. This research is quite informative for performance evaluation and improvement for general network systems.

Key words: network systems, free disposability principles, production possibility sets, data envelopment analysis, performance evaluation