Achieving Dependability Throughout the Development Process: A Distributed Software Experiment
IEEE Transactions on Software Engineering
An experiment in estimating reliability growth under both representative and directed testing
Proceedings of the 1998 ACM SIGSOFT international symposium on Software testing and analysis
IEEE Software
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Digital computers are being used more frequently for process control applications in which the cost of system failure is high. Consideration of the potentially life-threatening risk, resulting from the high degree of functionality being ascribed to the software components of these systems, has stimulated the recommendation of various designs for tolerating software faults. Such designs are not panaceas, for they still entail — as did the fault intolerant designs they are superceding-an unknown probability of failure. The paper discusses four reliability data gathering experiments which were conducted using a small sample of programs for two problems having ultrareliability requirements, w-version programming for fault detection, and repetitive run modeling for failure and fault rate estimation. The experimental results agree with those of Nagel and Skrivan in that the program error rates suggest an approximate log-linear pattern and the individual faults occured with significantly different error rates. Additional analysis of the experimental data raises new questions concerning the phenomenon of interacting faults. This phenomenon may provide one explanation for software reliability decay. The fourth experiment underscored the difficulty in distinguishing between observations of deficiencies in the design of the algorithm and observations of software faults for real-time process control software. These experiments are a part of a program of serial experiments being pursued by the System Validation Methods of NASA-Langley Research Center to find a means of credibly performing reliability evaluations of flight control software.