The use of Ward and Mellor Structured Methodology for the design of a complex real time system

The product ISA (Initialisation and Support Application), is a real time system which provides the soft functionality for the Node Support Computer of the ICL SX Node. Its main functions are control of initial program load, error management of fatal node hardware and software failures, support of in-line recovered node failure, support of remote diagnostic access to the node and support of `ancillary´ units (e.g. Power Control System). A requirement of the ISA Project was to improve productivity and delivered product quality from that achieved with the earlier equivalent products. To meet this requirement decisions were made to put increased emphasis on the analysis and design phases, to introduce a design methodology and to introduce design support tools. It was decided that the ISA Project should adopt an established and proven methodology. The authors discuss the adoption of the Ward and Mellor Methodology which is based on the Yourdon Systems Analysis and Design Technique