It can be regarded as an engineering practice to deal with the problems of large-scale complex systems by combining quantitative and qualitative system ideas and methods, whether it is the design or organization of the system or the management of the system, which is collectively called 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. All the factors are interrelated and mutually restricted. 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. ② 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.
System engineering is a branch of system science, which is actually the practical application of system science. It can be used in all aspects of large-scale system, including human society, ecological environment, natural phenomena, organization and management, such as environmental pollution, population growth, traffic accidents, arms race, chemical process, information network and so on. System engineering is a theory and method that takes large-scale complex systems as the research object, and designs, develops, manages and controls them according to certain purposes, so as to achieve the best overall effect. System engineering is an engineering technology. However, systems engineering is a major engineering technology category, including many kinds of engineering technologies. It covers a wide range, including mathematics, physics, chemistry, biology and other natural sciences, as well as sociology, psychology, economics, medicine and other disciplines related to people's thinking, behavior and ability. The basic theories needed by system engineering include operational research, cybernetics, information theory, management science and so on.
Definition of system engineering
1. [America] Chesner (1967)
Although each system is composed of many different special functional parts, and these functional parts are interrelated, each system is a complete whole, and each system has a certain number of goals.
System engineering is a method to balance the objectives, find the optimal solution in an all-round way, and make all components coordinate with each other to the maximum extent.
2. Japanese industrial standard JIS 8121(1967)
System engineering is a technology to analyze and design the components, organizational structure, information flow and control mechanism of the system in order to better realize the system purpose.
3. [America] Morton (1967)
System engineering is a method used to study production machinery with automatic adjustment ability, as well as information transmission devices, service machinery and computing machinery like communication machinery. Is the research, design, manufacture and application of these machines. 4. System Committee of American Quality Management Association (1969).
System engineering is a special project that applies scientific knowledge to design and manufacture systems.
5. [Japan] Terano Shoulang (197 1)
System engineering is the general name of ideas, steps, organizations and methods adopted in the rational development, design and application of systems.
Basic engineering.
6. Encyclopedia Britannica (1974)
System engineering is an engineering technology that effectively combines the knowledge in the existing branches of disciplines to solve the integration problem.
7. Encyclopedia of the Soviet Union in English (1976)
System engineering is a science and technology to study the design, establishment, testing and operation of complex systems.
8.[ Japan] Beowulf, Mihura (1977)
The difference between systems engineering and other engineering is that it is a science that spans many disciplines and a marginal science that fills the gaps in the boundaries of these disciplines. Because the purpose of system engineering is to develop a system, and the system involves not only the engineering field, but also the social, economic and political fields.
9. Qian Xuesen (1978)
Systems engineering is the technology of organization and management. The extremely complex research object is called system, that is, the organic whole with specific functions consists of several interacting and interdependent components, and the system itself is a part of the larger system to which it belongs. System engineering is a scientific method to organize and manage the planning, research, design, manufacture, test and use of this system, and it is a scientific method of universal significance to all systems.
1940 was first applied and system engineering was proposed. When Bell Laboratories developed the telephone communication network, it divided the development work into five stages: planning, research, development, application and general engineering, and put forward the principle of queuing theory. 1940 Manhattan, USA plans to develop an atomic bomb to coordinate the application of system engineering principles. Two examples of conscious application of systems engineering methods and great achievements are the Apollo program of American moon landing rocket and the Nordic transnational power grid coordination program.
System engineering can also be used in many aspects, such as optimal control of chemical production design process, information network operation and so on. At present, some universities have set up systems engineering majors.
The purpose of system engineering is to solve the overall optimization problem. Starting with the complex problems of the whole, it is considered that the whole is greater than the sum of the parts, and some parts are inferior but the whole can be optimized. Some problems, such as telephone network, can not only study the quality of a single telephone, but also start with the overall network, which is contrary to Descartes' methodology.
The concept of systematic evaluation
System evaluation refers to the process of determining the attributes of the object system according to the goal and transforming them into objective quantification or subjective utility (the degree of meeting the requirements of the subject), that is, defining the value of the system.
According to the evaluation project can be divided into
After the target evaluation determines the system target, it is necessary to carry out target evaluation to determine whether the target is reasonable;
After the target of scheme evaluation is determined, scheme evaluation should be carried out to select the best scheme;
Design evaluation evaluation system design.
Planning evaluation and planning evaluation
According to the chronological order of evaluation
Pre-evaluation before system development is an evaluation to improve system performance in the process of system planning research. (Because there is no system entity, the method of prediction or simulation is generally adopted. )
Mid-term evaluation The evaluation made during the implementation of the system plan.
Post-event evaluation, evaluation after the completion of development, and evaluation of whether the system has achieved the expected goal.
After running for a period of time, the tracking and evaluation system will find some unexpected aftereffects, which need to be re-evaluated.
According to the evaluation content
Technical evaluation Technical evaluation is carried out around the system function, and it evaluates whether the technical scheme of the system can realize the required function.
Economic evaluation is carried out around economic benefits, and the content is mainly economic feasibility analysis represented by cost benefit.
Social evaluation is an evaluation of the benefits or influences brought by the system to society.
Comprehensive evaluation is a comprehensive evaluation of the value of the system scheme based on the above three aspects.
Evaluation principle
Ensure that the evaluation has certain objectivity.
So as to ensure the comparability of the schemes.
Evaluation indicators should be systematized.
Evaluation criteria and utility function
In a multi-objective system, different objectives should be measured by different standards. If we want to evaluate the acceptability of an alternative to all objectives as a whole, it is necessary to standardize the above standards expressed in various units of measurement into a unified quantitative scale or measurement.
Single evaluation method
Single evaluation method mainly refers to the method of quantitative evaluation of a certain aspect of the system by using economic theory and technical level.
Economic evaluation methods mainly include value analysis method, cost-benefit method and profit evaluation method.
Technical evaluation methods mainly include feasibility analysis and reliability evaluation. Only the cost-benefit method and feasibility analysis method are introduced here.
analytic hierarchy process
1 principle of analytic hierarchy process
Analytic Hierarchy Process (AHP) is an effective method to deal with some complex problems in system engineering that are difficult to be analyzed by other quantitative methods, and it is also an objective method to sort out and synthesize people's subjective judgments.
Basic principles of analytic hierarchy process
To use analytic hierarchy process (AHP) to analyze the system, we must first hierarchical the problem. According to the nature of the problem and the overall goal to be achieved, the problem is decomposed into different components, and each factor is aggregated and combined at different levels according to its interrelated influence and subordinate relationship, forming a multi-level analytical structure model.
Top level: indicates the purpose of solving the problem, that is, the overall goal to be achieved by hierarchical analysis;
Intermediate layer: including criterion layer and index layer, indicating the intermediate links involved in adopting a certain scheme to achieve the predetermined overall goal;
Bottom layer: indicates various measures, strategies and schemes adopted to solve problems.
Application fields of analytic hierarchy process;
1, resource and environment assessment
Including petroleum resources evaluation and environmental pollution control scheme evaluation.
2, science and technology evaluation
Including industrial science and technology level evaluation, regional science and technology comprehensive strength evaluation, scientific and technological achievements evaluation;
3. Educational evaluation
Including teaching quality evaluation, comprehensive evaluation of college students, quality evaluation of graduates, etc.
4, manufacturing system evaluation
Including weapon system evaluation, anti-tank missile weapon system scheme evaluation and so on.
5. Project evaluation
Evaluation of water conservancy project development scheme, comprehensive evaluation of mining method feasibility scheme, etc.
6, personnel and social system evaluation
Leadership assessment, professional and technical personnel evaluation, economic benefit evaluation of small and medium-sized enterprises, comprehensive strength evaluation of cities, etc.
Basic principles of analytic hierarchy process
To use analytic hierarchy process (AHP) to analyze the system, we must first hierarchical the problem. According to the nature of the problem and the overall goal to be achieved, the problem is decomposed into different components, and each factor is aggregated and combined at different levels according to its interrelated influence and subordinate relationship, forming a multi-level analytical structure model.
Calculation problems of analytic hierarchy process
The concept of decision-making
In a narrow sense, decision-making refers to making a choice among several behavior schemes; Broadly speaking, decision-making also includes all thinking activities before making the final choice.
Decision analysis includes collecting feasible schemes, predicting the future, establishing target set, optimizing and analyzing various feasible schemes and giving results. Every link of work depends on the knowledge, experience and courage of decision makers and experts.
Natural state (state or condition for short)
It is an objective environmental condition that is not transferred by the subjective will of decision makers.
increase and decrease
Profit and loss status of corresponding schemes under different natural conditions.
Graphic meaning in decision tree
(1) Take the box as the decision point, the circle as the state point, and the small triangle as the profit and loss value at the end of the tree;
(2) Branches extracted from the box are called scheme branches, and each scheme is represented by a branch;
(3) Branches drawn by circles are called state branches, and each state is represented by a branch, with the probability of occurrence of the state indicated next to it;
(4) National risk decision.
The future situation is unknown, but the probabilities of various natural states are known. The decision-making in this case is called risk decision-making, also called random decision-making or statistical decision-making.
decision making under uncertainty
Although the decision-making under uncertainty knows several situations, he doesn't know which natural state will happen or the probability of it. In this case, there are several decision criteria, and the application of these criteria depends entirely on the experience and personality of the decision maker.
Calculate and compare the expected value of each option. If the decision-making goal is the maximum benefit, the alternative with the maximum expectation is taken; If the element of the profit and loss matrix is the loss value and the decision goal is the minimum loss, the scheme with the minimum expected value should be chosen.
Draw a triangle at the end of the branch to indicate the end, and indicate the profit and loss value of this state under this scheme.
Optimistic standard
Characteristics: The decision-makers who choose this criterion are optimistic about the objective situation and are willing to fight for every opportunity to get the best result.
Pessimistic standard
Features: Policymakers are pessimistic about the objective situation, always cautious and conservative about the worst result.
Compromise standard (optimistic coefficient standard)
Characteristics: The attitude towards objective situation is between optimist and pessimist, and it advocates balanced compromise.
Compromise income value = α× maximum income value +( 1-α)× minimum income value
Equal possibility standard
Features: It is assumed that all natural states have the same probability, that is, each natural state is given the same probability.
Regret value standard
Features: Set the highest value of each natural state as the ideal goal of the state, the difference between the highest value and other values in the state is called regret value, and the matrix of regret values is called regret value matrix. The standard of regret value is to minimize the maximum possible regret value in the future in decision-making.