X-Ware Reliability and Availability Modeling.

This paper addresses the problem of modeling a system's reliability and availability with respect to the various classes of faults (physical and design, internal and external) which may affect the service delivered to its users. Hardware and software models are currently exceptions in spite of the users' requirements; these requirements are expressed in terms of failures independently of their sources; i.e. the various classes of faults. The causes of this situation are analyzed; it is shown that there is no theoretical impediment to deriving such models, and that the classical reliability theory can be generalized in order to cover both hardware and software viewpoints that are X-Ware. After the introduction, which summarizes the current state of the art with regard to the dependability requirements from the users' viewpoint, the body of the paper is composed of two sections. Section H is devoted to system behavior up to failure; it focuses on failure rate and reliability, considering in turn atomic (or single component) systems and systems made out of components. Section III deals with the sequence of failures when considering restoration actions consecutive to maintenance; failure intensity, reliability, and availability are derived for various forms of maintenance. [ABSTRACT FROM AUTHOR]