A system is a set of parts, called elements, and the relations between those parts through which the elements are interdependent in forming some overall macro organization. Systems perform functions whereby they take in resources, perform some process upon them and generate some output of energy and entropy. Systems operate within some environment and have a boundary that defines the internal set of interdependent elements as distinct, and in some way autonomous, from their environment. Systems can be open or closed. Closed systems have a limited exchange of energy and resources with their environment and are governed by linear systems theory. Open systems in contrary have a high exchange of energy and resources with their environment, they are typically nonlinear and may be in a thermodynamic state of disequilibrium.