Alistair Mavin

Praxis Critical Systems Limited, London, UK

THIS CASE Study chapter reports on a project with a major international rail rolling stock manufacturer during requirements elicitation and system specification for new metro Trains. The project used the Praxis REVEAL1 requirements engineering method.

Scenarios were used to analyse Train requirements to derive specifications and domain knowledge. The same scenarios were then used as the contextual glue to show that the requirements had been satisfied by the specifications, given the domain assumptions. The scenarios were, therefore, a key part of the Satisfaction Argument used to show that the solution will satisfy the requirement. Similarly, scenarios were used in the analysis of Train specifications to derive requirements for the sub-systems, which also uncovered further domain knowledge.

The process produced Train specifications that were written at the right level of granularity. During the development of activity diagrams, engineers tended to write simple descriptions of the external behaviour of the system as a black box. Previously, they had tended to go into the detail of specifications too early.

The scenarios explicitly showed dependencies on domain assumptions, as well as dependencies between different sub-systems. This visibility helped sub-system suppliers to understand the environment in which their products would be used. Using this process, the sub-system ...

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