9308912 Tai In many real-time distributed systems where both performance and dependability are critical, the conditions affecting these two attributes in the system itself as well as its environment may change dynamically. In order to assure high performance dependable computing, a computer/communication system's operational strategies and requirements have to be adjusted responsively. The research studies adaptive performability management (performability is a combined measure of performance and dependability) for assuring performance and dependability goals simultaneously via run-time model-based decision making. The method will provide a computer system with the capability to determine, based on the underlying performability model, whether it achieves its performance and dependability goals. If not, it will select an alternative strategy. The objectives of this research are to investigate the utility of performability concepts and modeling techniques when the object system is in operation, and to investigate the effectiveness of the resulting methodology in assuring high performance dependable computing. Accordingly, the focus will be on: 1) methods of model construction which stress the tradeoffs among performance, dependability and other critical attributes and facilitate adaptive performability management, 2) methods of model solution which are sufficiently efficient to support run-time decision making, and 3) methods for evaluating the effectiveness of an adaptive performability management scheme. ***
