The ultimate objective of any system is the performance of some intended function. This function is frequently called the 'mission'. The term often used to describe the overall capability of a system to accomplish its mission is 'system effectiveness'. System effectiveness is defined as the probability that the system can successfully meet an operational demand within a given time when operating under specified conditions. Effectiveness is influenced by the way the system is designed, manufactured, used, and maintained. Thus the effectiveness of a system is a function of several attributes, such as design adequacy, performance measures, safety, reliability, quality, productibility, and maintainability. The disciplines of assurance sciences help to increase the overall effectiveness of any system. The assurance sciences are engineering disciplines that have the common objective of attaining product integrity (product does what it says it is supposed to do). The term 'product assurance' is also used by some companies. This passage is concerned with the reliability, maintainability, serviceability, and availability aspects of the product assurance system.