Information system is a data-intensive, man-machine interactive computer application system whose main purpose is to provide information services. Technically speaking, it has four characteristics: it involves a large amount of data, which generally needs to be stored in auxiliary memory, and only a small part of the data to be processed is temporarily stored in memory; Most of the data is persistent, that is, it does not disappear with the end of the program, but needs to be stored in the computer system for a long time; These persistent data are shared by multiple applications, even in a unit or a larger scope. Besides the basic functions of data collection, transmission, storage and management, it can also provide users with information services such as information retrieval, statistical report, transaction processing, planning, design, command, control, decision-making, alarm, prompt and consultation.