We must look for ways to limit this risk as we design large-scale solutions. He described a technique in which designs for a system are evaluated by proposing a series of possible change scenarios, and actively reviewing the design in the light of those change scenarios. This question would then be analyzed with the system s designers who would actively walk you through a response to this question with reference to the design and its elements. I have found this active design review approach to be very useful in a number of situations. We used Parnas s approach to create a series of change scenarios, and actively walk through these scenarios with the designers responsible for the system.
Any system is designed to operate within an assumed context.
This context dictates many of the decision that will be made. In fact, to gain efficiencies we actively optimize the system for that context. All of this is thrown into confusion when the context is unexpectedly changed. When a system is asked to operate in a context for which it was not designed, unpredictable results arise. This was a consequence of reusing previously designed software for Ariane 4 in the new Ariane 5, placing it into an environment for which it had never been designed.