A Study on User-Oriented Software Assessment Methods Considering Safety and Availability

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Software availability is defined as the attribute that the software system is operable and available whenever we want to use it. And software safety is defined as the attribute that it will not cause an unsafe condition. Those attributes are user-oriented quality characteristics of software systems. This research investigates the user-oriented software reliability assessment methods in consideration of software availability and safety. At first we discuss the basic idea of software availability modeling and the difference between modeling for software and hardware systems. Markov processes are applied to the descriptions of the time-dependent behaviors of software systems alternating between up and down states ; then the processes of software reliability growth and the increase in difficulty of restorations are incorporated as well. We also refer to several extended models reflecting the software failure-occurrence phenomenon and the restoration scenario peculiar to the user-operational phase, considering computation performance, and combining a hardware and a software subsystem. Then, we can derive several user-oriented quantitative measures for software availability and safety assessment such as software safety, instantaneous software availability, average software availability, and interval software availability. Furthermore, by using JAVA languages we can develop a software management tool which incorporates the user-oriented software reliability assessment methods.