Software reliability trend analyses from theoretical to practical considerations

This paper addresses the problem of reliability growth characterization and analysis. It is intended to show how reliability trend analyses can help the project manager in controlling the progress of the development activities and in appreciating the efficiency of the test programs. Reliability trend change may result from various reasons, some of them are desirable and expected (such as reliability growth due to fault removal) and some of them are undesirable (such as slowing down Of the testing effectiveness). Identification in time of the latter allows the project manager to take the appropriate decisions very quickly in order to avoid problems which may manifest later. The notions of reliability growth over a given interval and local reliability trend change are introduced through the subadditive property, allowing: better definition and understanding of the reliability growth phenomena; the already existing trend tests are then revisited using these concepts. Emphasis is put on the way trend tests can be used to help the management of the testing and validation process and on practical results that can be derived from their use; it is shown that, for several circumstances, trend analyses give information of prime importance to the developer