Definition of System: General Case

system is an arrangement of parts or elements that together exhibit behaviour or meaning that the individual constituents do not.

“Parts” is the more general term, going back to Aristotle’s phrase “the whole is more than the sum of the parts”. “Elements” has become established as the preferred term in recent systems engineering usage. The two terms are sometimes used interchangeably, but in some domains they have specific meanings (e.g mechanical part, chemical element, part of a whole, part played by an actor or role).

The concept of “behaviour or meaning of the whole not exhibited by the individual constituents” is often referred to as “emergence”, and is the defining characteristic of “systems” that distinguishes them from “non-systems”. However, we avoid using the term in this definition because of the risk of confusion with the other notion of “emergence”, which denotes surprise where such properties “emerge” that could not be foreseen or anticipated.

The goal of systems engineering is, then, to select, adjust, and arrange the parts or elements so as to achieve the desired whole-system properties when the system of interest is used as intended.

Physical and Conceptual systems

Systems can be either physical or conceptual, or a combination of both.

Systems in the physical universe are composed of matter and energy, may embody information encoded in matter-energy carriers, and exhibit observable behaviour.

Conceptual systems are abstract systems of pure information, and do not directly exhibit behaviour, but exhibit “meaning”. In both cases, the system’s properties (as a whole) result, or emerge from:

  • the parts or elements and their individual properties; AND
  • the relationships and interactions between and among the parts, the system and its environment.
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