Availability and other performance measures of software systems under imperfect maintenance

In this paper we develop a model for the operational phase of a software system which incorporates the uncertainty of error removal and the time spent in correcting errors. Expressions for various measures of software performance, e.g. distribution of time to a specified number of remaining errors, the expected number of errors detected and corrected in time t, and software system availability are derived. Numerical examples are used to illustrate these results.