The system analysis starts with the system requirements and establishes the system user model from the user's point of view. The user model conceptually expresses the system requirements and the relationship between the system and users. Based on the user model, the system analysis establishes a logical structure with strong adaptability and independence from the system implementation environment.
The analysis stage is independent of the system implementation environment, which can ensure the relative stability of the established system structure and facilitate the maintenance, transplantation or expansion of the system.
In the system analysis stage, the logical structure of the system should comprehensively reflect the function and performance of the system from the following three aspects:
(1) information. Fully describe all the information processed in the system;
(2) behavior. Fully describe the processes or functions required for system state change;
(3) indicate. Describe the external interface and interface of the system in detail.
2. Systems engineering deals with the problems of large-scale complex systems by combining quantitative and qualitative system ideas and methods. Whether it is system design, organization establishment or system management, it can be regarded as an engineering practice, collectively referred to as system engineering.
After the second world war. In order to meet the needs of socialized mass production and complex scientific and technological systems, some theories, strategies and methods in natural science and social science are gradually linked, and modern mathematics and computers are applied to solve the control problems of organization and management of complex systems, so as to achieve the purpose of optimal design, optimal control and optimal management. System engineering is a comprehensive management engineering technology, involving many disciplines of natural science and social science. The basic elements of system engineering are: people, things, money, goals, machinery and equipment, information and other six elements. Various factors are interrelated and restrict each other. System engineering can be roughly divided into three stages: system development, system manufacturing and system application, and each stage can be divided into several small stages or steps. The basic methods of system engineering are: system analysis, system design and comprehensive evaluation. Specifically, the system is described by mathematical model and logical model, and the operation of the system is reflected by simulation, and the optimal combination scheme and optimal operation scheme of the system are obtained. Since 1970s, systems engineering has been widely used in the fields of transportation, communication, enterprise production and management, and it also has application value and broad prospects in the field of sports. Its basic feature is that the research object is regarded as a whole, which requires that the research of any object must be comprehensively investigated from its composition, structure, function, mutual connection, historical development and external environment, so as to achieve the unity of analysis and synthesis. The most commonly used system engineering method was founded by Hall, one of the founders of system engineering, and it is called three-dimensional structure diagram: ① Time dimension. For a specific project, from planning to updating, the whole process can be divided into seven stages: planning, drawing up a scheme, development, production, installation, operation and updating. ② Logical dimension. A large-scale project can be divided into seven steps: clear purpose, index design, system scheme combination, system analysis, optimization, decision-making and scheme formulation. ③ Knowledge dimension. Systems engineering needs all kinds of professional knowledge. Hall divides these knowledge into engineering, medicine, architecture, business, law, management, social science and art, and calls these professional knowledge the knowledge dimension.
3. System Science System science is a new scientific group with system thought as its core. It includes many disciplines, such as system theory, information theory, cybernetics, dissipative structure theory, synergy theory, operational research, systems engineering, information dissemination technology, control management technology and so on. It is a comprehensive science with the fastest development since the middle of the 20th century. These disciplines were born and developed in different fields. For example, system theory was put forward by Bertalanfi in Theoretical Biology in 1930s. Information theory was founded by Shennong to solve the problem of modern communication. Cybernetics was founded by Wiener to solve the technical problems of automatic control. Operational research was formed by some scientists who applied mathematics and natural science methods to participate in military decision-making during World War II. System engineering was born to solve the organization and management problems of modern large-scale scientific engineering projects. Dissipative structure theory and synergetic theory are founded by theoretical physicists to solve the control problem of orderly development of natural systems. They used to be independent scientific theories, but they are closely related and infiltrated with each other, and tend to be integrated and unified in their development, which tends to form a unified discipline. Therefore, many scholars at home and abroad believe that a systematic science with a strict theoretical system can be formed by taking the system as the center and linking the emerging science. As early as the 1960s and 1970s, some American scholars saw that the development of systems engineering was closely related to related basic theories, and that systems engineering and cybernetics' large-scale system theory permeated each other, so they called systems engineering systems science.