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.┬áSystems 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.