We have argued elsewhere that formal methods are useful in the design of interactive systems [Dix 1985, Dix 1987a, Dix 1987b]. Further, we have argued that when formal methods are being used anyway for system design, it is essential that human factors considerations be explicitly included. However, when we consider the relationship between the requirements of the process of interactive system design, and the process of formal development, several conflicts occur. These problems are not unique to interactive systems design, but are inherent in the concept of formal development; it is just that the rigours of interactive systems intensify and bring these problems to notice.
After considering the differing requirements of the two domains of interactive systems design and formal refinement, we will proceed in a dialectic style. Conflicts will become apparent between the sets of requirements, which we will attempt to resolve, eventually leading to the need for, and proposals for techniques for structural transformation of systems at the module level during refinement. The technique of interface drift will be discussed in detail.
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interface drift
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