Validation of ultrahigh dependability for software-based systems

omputers are used in an increasing number of applications in which their failure may be very costly, in terms of monetary loss and/or human suffering. Examples include control of aircraft, industrial plants, railway and air traffic, weapons and military units, banking and commercial transactions. To reduce the cost to society of operating these computer-controlled systems, dependability requirements for their essential computers are often very high. The most frequently quoted requirement is