A system is defined as a set or group of interacting, interrelated or interdependent elements or parts, that are organized and integrated to form a collective unity or a unified whole, to achieve a common objective.[4][5] This definition lays emphasis on the interactions between the parts of a system and the external environment to perform a specific task or function in the context of an operational environment. This focus on interactions is to take a view on the expected or unexpected demands (inputs) that will be placed on the system and see whether necessary and sufficient resources are available to process the demands. These might take form of stresses.