Development of agent systems has been surveyed, to classify and arrange characteristic functions of the agents, and to grasp the realization situation of these agents in their development. In addition, prospective functions of information retrieval systems using the agents at maximum and functions to be developed among these in the future are clarified. The agents are characterized by the expression function, communication function, planning function, adaptive function, and learning function. The agents are desired to be classified into interface agents whose works are to respond to individual workers, coordinator agents which conduct works with high pervasion, such as assignment of works and their control, and task agents which conduct specialized works for individual examples. Thus, design and configuration of the agent system, and improvement and expansion of system functions can be effectively and easily conducted. 52 refs., 5 figs., 3 tabs.