International Encyclopedia of Systems and Cybernetics

A relation between two terms (E. SCHWARZ, 1993,p.6)

More generally, any function implies a more or less permanent causal relationship exerted by some element on another element.

This correspond to a process – generally iterative – that must be carried out to maintain the system's stability, its goal(s) or general purpose, or even, its existence.

The concept of function is closely related to various other ones:

- The iteration of a functional process evoques the appearence of sets of elements permanently interrelated in a specific fashion, namely a structure.

- Functional processes must be harmonized with each other in the system if it is to maintain itself globally, i.e. as an organized whole. They must remain within the limits of the organizational closure specific of the system.

- Functional processes are most generally cyclical (i.e., in homeostatic systems) and maintain some critical values between defined upper and lower limits This is generally obtained through alternating positive and negative feedbacks.

- Functional processes are frequently interconnected in a circular way, i.e., included in hypercycles. A process may be internally hypercyclical.

- An excessive stress endured by a system 's function may progressively bear upon other functions and lead to general disabling of the system. See: "General Adaptation Syndrome".

In a different perspective, more related to far-from-equilibrium situations in systems, I. PRIGOGINE considers that: "Dissipative structures… form a bridge between function and structure" (1976, p.95). The shaping of new functions and new structures are concomitant phenomena.