Building BridgesI have often used the analogy of building a bridge to explain to business colleagues the difference between Rapid Application Development (RAD) and Waterfall.Let’s say that we are in the middle ages and the Mayor of Kingston-upon-Thames is evaluating whether or not to build a bridge over the river to the north side, to replace the current ferry. The whole area has been growing rapidly and a bridge at Kingston should give his town a lead against competing local towns like Ham and.