The system has a unity of purpose in the accomplishment of its goals, functions, or desired outputs. A system must be able to differentiate itself from external events, objects or other systems outside certain definable boundaries. Outside the defined boundaries is an environment. A change in the environment can result in a change in the system. The state of a system at any moment in time contains a set of relevant properties restricted to that time frame.
Health systems tend to be very complex.
Complex systems, such as health systems, are also defined by their hierarchical or nested structure of subsystems, each having some meaningful function while interacting to produce the overall system. It is completely self-contained, and elements in the systems do not interact with elements in the environment. They are autonomous. These systems have the standard inputs, processes and outputs. Sometimes the output of a system is used to regulate the input of a system, especially when a desired output is not achieved and the inputs and processes must be adjusted.