Markovian model for user-perceived software service availability measurement with operation-oriented restoration

This paper discusses the stochastic model for measuring software service availability; this is one of the customer-oriented attribute and defined as the attribute that the software system can successfully satisfy the end users' requests. From the viewpoint of a user, occurrence of a system failure is recognized when either one of the following two events arises: a software failure occurs when the user is using and operating the system, or a usage request occurs when the system is down. We propose and derive three kinds of novel service-oriented software availability assessment measure named (!) the software service availability in use, (ii) the software service unavailability due to request cancellation, and (iii) the software service unavailability under restoration; these are given as the functions of time and the number of debuggings. The time-dependent behaviors of the system alternating between up and down state and the user's request are described by a Markov process. Then we incorporate the operation-oriented restoration scenario into the model, i.e., we consider the following two types of restoration: one is the restoration with debugging and the other is without debugging. Furthermore, the dynamic software reliability growth process, the upward tendency in difficulty of debugging, and the imperfect debugging environment are also included in software service availability modeling. Finally, we present several numerical examples of these measures for software service availability analysis.