ABSTRACT
Reliability is the probability that a device properly performs its intended function over time when operated within the environment for which it is designed. Observe that there are four specific attributes of this definition of reliability. The four attributes are: probability; proper performance; qualification with respect to environment; and time. Among reliability specialists, it is generally accepted that there are four generic types of structural relationships between a device and its components. They are: series; parallel; k out of n; and all others. A k-out-of-n system is one in which the proper function of any k of the n components that comprise the system implies proper system function. A coherent system is one for which the system structure function is nondecreasing in each of its arguments. The treatment of component and system status is limited to the case in which system state and component states are binary.
