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Systems Engineering Review 系统工程 一 ．Four Basic Attributes of the System (1) Assemblage. A system consists of a plural number of distinguishable units, which may be physical or conceptual, natural or artificial. (2) Relationship. Several units assembled together are merely a group or a set. For such a group to be admissible as a system, a relationship or an interaction must exist among the units. (3) Goal-seeking. An actual system as a whole performs a certain function or aims at single or multiple objectives. Wherever these objectives are attained at their maximum/minimum levels, system optimization is said to have been performed. For this purpose it is necessary to be able to measure, objectively or subjectively, the degree of attainment of the objectives. An objective that is measurable by any means is called a goal. (4) Adaptability to environment. A specific, factual system behaves so as to adapt to the change in its surroundings, or external environment. This external environment influences and is influenced by the system, in that matter and/or energy and/or information are received from and given to each other. A system that is capable of controlling itself in such a way as to be always optimal even under changes in the external environment is called an adaptive system. 二 Systems Defined Four Definitions of Systems On the basis of the foregoing considerations, the four essential definitions of systems can now be given as follows . (1) Abstract (or basic) definition. On the basis of the first two attributes above, a system is a collection of recognizable units having relationships among the units. Under this definition, general system theory has been developed, wherein things are deliberated theoretically, logically, and speculatively. (2) Structural (or static) definition. On the basis of all four attributes, a system is a collection of recognizable units having relationships among the units, aiming at specified single or multiple objectives subject to its