An approach to addressing the performance issues in the early stages of the design of a software system is presented. The module decomposition of the trouble-analysis subsystem is considered as an example in using this approach. Each module is characterized by its hidden information, external behaviour, and a set of performance parameters. A working system is built using these modules, and it is found that the response time of the working system varies from over an hour to less than a minute by simply varying the value of the performance parameter. Consequently, the system could be tuned by simply varying the value of the performance parameter and not by restructuring the system. The values of the parameters are selected to minimize the response time. The approach is illustrated by a case study involving a pattern recognition system which isolates faults in circuit packs.>

This paper describes the form of an interface requirements document and a design method to produce it. Document and design are coupled by embedding the right questions in the document. The completed document answers the questions. Work described in this paper has grown out of practical experience and by reflecting on the general nature of requirements. The paper contains a design method for the construction of interface requirements at an application program level. The general nature of the material makes it applicable to a wide range of device interfaces.