International Encyclopedia of Systems and Cybernetics

A system able to selectively exchange matter, energy and/or information with its environment.

The selectivity is the key aspect, in space as well as in time. The system can be alternatively open or closed to some inputs or outputs. This means that the system has a more or less extensive capability to control its inputs and outputs in relation to its needs. This secures the individuality of the system and connects the open system concept with the autopoiesis and organizational closure ones.

R. ROSEN expresses the consequences as follows: "von BERTALANFFY explicitly showed that a basic characteristic of biological systems could be approached entirely through a functional or relational criterion (i.e. that the system be open) rather than through reductionist analysis of the specific particles of which any particular system happens to be composed".

"(He also stressed) the relation between regulatory phenomena in biology, particularly those which appear to involve purposiveness, and the formal concept of stability" (1973, p.176).

Furthermore, ROSEN adds that von BERTALANFFY had an implicit intuition that the classical thermodynamics was at a loss to explain living systems, a fact that was later explained by I. PRIGOGINE, who introduced the needed amendments. And finally, von BERTALANFFY recognized that an open system could reach the same final state, using different lines of behavior (equifinality).

D. KATZ and R.L. KAHN describe as follows the main characteristics of open systems:

"- They undergo "repeated cycles of input, transformation. output, and renewed input

"- The law of negative entropy (?) states that systems survive and maintain their characteristic internal order only so long as they import from the environment more energy than they expend in the process of transformation and exportation" (1969,p.103). (The excess is used to maintain internal order… through the production of new elements characteristic of the system and used to replace elements of the same type).

"- They possess feedback devices that KATZ and KAHN interpret as follows: "The feedback principle has to do with information output, which is a special kind of energic importation, a kind of signal to the system about environmental conditions and about the functioning of the system in relation to its environment… The system thus maintains a steady state or homeostasis. This is a dynamic rather than a static balance, however" (Ibid).

"- They tend to differentiation and elaboration, both because of subsystem dynamics and because of the relationship between growth and survival" (Ibid).

"- They are equifinal which means "…that systems can reach the same final state from different initial conditions and by different paths of development" (Ibid).