RELATIONSHIP BETWEEN THE ACTIVITIES OF THE SOFTWARE PROCESS AND THE QUALITY OF THE SOFTWARE PRODUCT by

The main justification for process improvement is that the quality of the software product will improve as a result. This seems intuitive but unfortunately there is no empirical evidence to prove its validity yet. The purpose of this paper is to present a possible mapping between the activities of the software process and the quality of the software product. It is argued that the product quality characteristics should be one of the prime drivers when assessing and improving the quality of an organisation's software process as it is the quality of the product about which we are increasingly concerned. University Of Strathclyde Department Of Computer Science Research Report/94/171 Page 2 1 . Introduction 1.1. Software Product Quality The term "Software Product Quality" is a rather general concept that is influenced by many different variables, some of which are easier to quantify than others. To determine if one piece of software is of higher quality than another is a difficult task at present; it depends on our idea of quality. The ISO 9000 series of standards (known as BS5750 in the UK) defines quality as:"The totality of features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs" [1] This is a very general view of quality, intended to encompass all products, not just software. Fenton [2] sites three common definitions of software quality with very different connotations:"Fitness for purpose" "Conformance to specification" "Degree of excellence" The term "software quality" has different meanings for different people in a software organisation. A marketing managers view of the quality of a product will not be the same as a software engineers view. These views are often conflicting and the term quality cannot be defined in such a way as to encompass these. 1 . 2 . Software Quality Characteristics In the ISO definition given above, "totality of features and characteristics" implies that quality is comprised of many components. The idea of decomposing the intangible concept of software quality into a number of more discernible factors is not a new one and many attempts have been made to find a collection of measurable "-ilities" to achieve this goal. Any textbook on Software Engineering will lay testimony to this. By decomposing quality into a number of factors, we are essentially providing a definition of it. The first work in providing a software quality framework was conducted by McCall, Richards and Walker (1977) [3] after their well-known work at the Rome Air Development Centre in New York State. They produced a list of eleven factors or characteristics which they believed encompassed the range of aspects of software quality. Around the same time, Boehm et al (1978) [4] published an independent list of seven factors. Years later, Bowen, Wigle and Tsai (1985) [5] produced a longer list (thirteen factors) again from work at RADC. Later attempts included Grady and Caswell (1987) [6], Deutsch and Willis (1988) [7], Forse (1989) [8] and von Maryhauser (1990) [9]. University Of Strathclyde Department Of Computer Science Research Report/94/171 Page 3 Boehm et al McCall et al Bowen et al Efficiency Reliability Human Engineering Modifiability Portability Testability Understandability Efficiency Reliability Usability Flexibility Portability Testability Reusability Maintainability Interoperability Correctness Integrity Efficiency Reliability Usability Expandability Portability Verifiability Reusability Maintainability Interoperability Correctness Integrity Flexibility Survivability Figure 1.1 Software Quality Factors Although the lists are similar and appear to contain some identical factors, these are defined differently in each model. This multitude of proposals with many different definitions of characteristics resulted in a lot of confusion as to what software quality actually meant. It is for this reason that the ISO 9126 [10] model was developed, so that international agreement could be reached on what the software quality characteristics should be. The different models did have one thing in common; each was based on a Factor Criteria Metric paradigm whereby each quality Factor is composed of a number of Criteria which in turn can be assessed according to a number of defined Metrics. These metrics are actual measurements taken from components of the software product. It is interesting to note that further work has emerged since the publication of ISO 9126 (1991), for example Gillies (1993) [11].