Coarse Grained Retrenchment and the Mondex Denial of Service Attacks

Retrenchment is a framework that allows relatively unrestricted system evolution steps to be described in a way that gives an evolution step some formal content - unlike model based refinement, whence it emerged, which is inapplicable outside some fairly tightly drawn notion of `progress towards implementation'. In this paper, we introduce a `coarse grained' version of retrenchment, relating to system behaviours in the large, and exemplify it on the requirements issues surrounding a denial of service case study drawn from the Mondex Purse. We show that the coarse grained retrenchment framework gives a good account of this case study.