Usage Modelling: The Basis for Statistical Quality Contro

The testing method proposed in the Cleanroom methodology is Statistical Usage Testing. This testing technique is based on that the test cases represent the
operational profile. The failure data from testing is then used in a software reliability model to certify the reliability of the software. This paper introduces a new model for modelling the usage of the system, i.e. the operational profile. It is shown to cope with the state explosion problem encountered when applying a simple Markov model to large software systems. The proposed model
introduces a hierarchical Markov model, which is shown to solve the problems encountered in the ordinary Markov description. Users and services are represented so that the model can easily be extended when new users or services are added. It is concluded that the introduction of this model will make it possible to certify large software systems in the future. The model generates test cases providing failure data that can be used in software reliability models. The new model forms the basis for being able to apply statistical quality control to software systems.