We will argue that CALL can usefully be viewed as a subset of computer software engineering and can profit from adopting some of the recent progress in software development theory. The unified modelling language has become the industry standard modelling technique and the accompanying unified process is rapidly gaining acceptance. The manner in which these can be used as a design aid will be demonstrated using, as a concrete example, the London Metropolitan University "Interactive language learning" authoring package. We will show how, by applying such formal techniques, existing functionality has been improved and new functionality has been developed. This approach can lead to a greater understanding between the developer and the user, both student and teacher, as well as helping to bridge the gap between the second language acquisition expert and the software developer to the benefit of both. This development process has led us to believe that CALL, as the most advanced of the computer aided learning disciplines can also make a valid contribution to more general computer science in areas of interface design, evaluation and requirements analysis. Modern computer science is dominated by the "business model." We argue that CALL can offer an approach which is driven by both pedagogy and research and which offers what we might call a "public service model" but which we will call "process model" for the sake of political neutrality. A case study will explain how these ideas have been applied in practical development of our authoring package and on-line course material. In particular, we show how the use of Java Server technology has provided tracking and improved online assessment. (Contains 2 notes and 33 figures.)