International Encyclopedia of Systems and Cybernetics

1) An operation intended "to make the components of a system increasingly fused and interactive" (B. BANATHY, 1973, p.87).

2) The state of a whole whose components are closely interactive.

W.C. ALLEE et al write: "Division of labor and integration are associated principles. Integration has no function unless there are differentiated parts that must act in relation to the whole. Specialization of function cannot occur unless the specialized parts are coordinated. Efficient homeostasis follows an increase in the special functions of the integrated parts. These principles apply to every organismic level, from the cell to the ecosystem, but are particularly well exhibited by the population of a colony of social insects" (Quoted by Ch.H. LAWSON, 1963, p.114).

R.N. ADAMS states: "… when a level is formed it not only receives inputs from its components but also involves self-organization at each emergent higher level" (1988, p.183).

Any progress towards integration supposes constraints: any integrative operation specifies well defined interactions among parts, generally by preventing other interactions. M. DODDS and G JAROS write: "Integration… represents pattern and order, it tends toward simplicity and cohesion (morphostatic)" (1994, p.1417).

It also supposes the emergence of a higher level communications network, whose links precisely define the newly instated constraints.

Composite systems are less integrated than complex systems. Complexity is indeed closely related to integration since the better specified and more precise definitions of interactions tend to lead towards more differentiation of the various parts of the system, which thus becomes more heterogeneous.

Integration of very complex systems is more difficult and costly, as the number of components and subsystems increases, since more – and more complex – regulators are necessary to maintain homeostasis.

Integration is, in principle, an irreversible process or state. The break-up of the prescribed interactions – even when crossing quite narrow limits – leads to the systems disintegration.

The integration process is linked to the progressive emergence of constraints within the system: rules of behavior of the elements, rules for their interactions.

In ASHBY's terminology, an integrated system is more or less richly joined.

There is an optimum level of integration for any specific system, which is, unfortunately, very difficult to perceive and, still more so, to specify. Below this level, the system is not as efficient as it could be. Above it, it becomes clogged and slow to react to any inside or environmental disturbance.

In any case, the system retains its adaptability and efficiency only when it still counts with sufficient redundancy.