International Encyclopedia of Systems and Cybernetics

1 the concept

D. Mc NEIL considers control as "& the reordering of activity with reference to ends". In the toroidal paradigm he proposes, "manifestations of control can be identified with the orientation and strength of a toroidal center, taken as a channel, a stem, a conduit, or even a gyroscopic axis complementary to a looping flow of content" (1993, p.11).

Aside from this very general view, we need a better understanding of the ways controls work, as related to organization, stability and goals or purposes.

J.Z. YOUNG writes that control is: "The regulation of the operation of a system by a program of instructions, often using sensors to detect deviations from a reference standard and initiate corrections" (1978, p.291).

St. KATZ writes: "In essence, control simply means the regulation of magnitude. Now to say that something is regulated implies that it may assume any of a number of values, i.e. it may vary or is variant. Yet, the very fact that we refer to it as "it" or "something" implies that the something being regulated has also a permanent aspect about it, i.e., has a characteristic that remains constant or is invariant" (1976, p.43).

According to E. JANTSCH, control "is geared to stability and to the optimization of specific parameters under a set of fixed constraints" (1975, p.283).

All systems have controls, generally many ones, since they include a number of processes and functions that must be maintained within specific maxima and minima.

However, control is closely related to variance in the environment, which is generally the cause or the trigger of internal variance of the controlled system.

As any control is basically a constraint, the concept of control implies an algorithm relative to the necessarily predefined limits. However, such an algorithm may be implicit, as for example in the natural and reciprocal control of animal and/or vegetal populations.

In machines, control is normally ensured by some preconceived mechanism.

As a constraint (in ASHBY's terminology) any control prohibits certain states and transformations and allows others, under specific conditions.

Control also implies hierarchy, since the controlled process or function is submitted by some command device to limitations, that it cannot normally modify.

In many cases hierarchic control is multilevel: subsidiary or local controls are, in turn, commanded by more global ones. In H. PATTEE's words, hierarchic control aims at the: "Optimization of the level of constraints in forming new structural levels and in the optimization of loss of detail in forming new descriptive levels" (1973, as quoted by E. JANTSCH, 1975).

However, the concept of control is in some cases ambiguous or misinterpreted.

W.T. POWERS states: "A is said to control B if, for every disturbing influence acting on B, A generates an action that tends strongly to conteract the effect of the disturbing influence on B".

He adds: "It is important to understand from the start that this definition doesn't fit many of the common usages of the term. For example it is said in chemistry that temperature controls the rate of a chemical reaction. But that doesn't fit the definition: if some independent influence tends to change the rate of the reaction (stirring the mixture for example), the temperature will not change so as to counteract the effects of the disturbance on the reaction rate" (1995)

Control, as meant by POWERS, always implies the existence of a willful controller or a goal-seeking device purposedly introduced.

2, the mechanism⁵

So-called "devices" are proper to man-made systems. Even so, some are abstract as, for example, controls on money supply by interest rates or the highway code which aims at regulating drivers habits by way of norms. On the contrary, no material mechanisms are conspicous in natural systems like populations, or biotopes: here the control is diffuse and statistical in character (see Markovian process).

Living systems have biological control devices, which regulate, for example, blood pressure, glycogen rate or perspiration. But these devices performance is automatic and non-volitive.

In any case, as stated by V.G. DROZIN, it is impossible to "… effectively control a complex system by using only promoters or suppressors" (1975, p.11).