System Architecture and Complexity

4The System and its Invariants

4.1. Models

The “system” object itself can undergo evolutions that may be large or small, under pressure originating from three sources: (a) users who require new functions and/or other modes of operation, for new uses; (b) technological innovations that will allow the system to increase its capacities and provide the users with competitive advantages; and (c) the environment with its uncontrollable hazards. The objective of these evolutions is to improve the system’s service contract with regard to its users, or simply to survive.

For developments of this kind to be possible, whilst avoiding re-doing everything, the system must have certain abilities that are independent of the desired evolutions so that these can become easily integrated and constitute an operational evolution of the system.

A little like the axioms of a mathematical theory, these abilities will constitute the invariants of the system, which must not change under any circumstances, and if they do, they will compromise the general equilibrium. These invariance properties can be immaterial, important in the entire system, such as compliance with a procedure, or can be conveyed by a particular piece of equipment.

For example, the equilibrium between supply and demand for the electrical system is an invariant property. Each piece of production equipment is supposed to guarantee its production by contract. Compliance with a 220/380 volts potential, or frequency and synchronization ...