Maintenance modelling for computer-based systems

A framework is presented for incorporating maintenance into a dependability analysis methodology for computer-based systems. Two types of maintenance are considered: failure-driven maintenance and time-driven maintenance. Failure-driven maintenance or repair is carried out when the system (or component) performance deviates from its expected performance and consists of all tasks performed to restore the functional capabilities of failed items, principally diagnosis and repair. Timedriven or scheduled maintenance is conducted on a speci c time schedule in order to prevent system failure. There may be dependencies between different components of a system with regard to their maintenance plans. These dependencies arise either because a component has maintenance priority over one or more components or because the maintenance of a certain component implies the maintenance of other components. Constructs are presented for modelling these dependencies in the context of dynamic fault tree analysis and a methodology is developed for solving the fault tree. The dynamic fault tree constructs effectively capture the failure dependencies between components. The approach is illustrated with an example based on a water deluge system.