Intranet Project – Rad Or Waterfall?

Building Bridges

I 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 Richmond (who also have their own ferries).

However, building a bridge presents problems. Firstly, the bedrock north and south of the river are very different. Secondly, the river is still tidal at this point and its path continues to vary across the floodplain. Finally – and perhaps most importantly – there is no guarantee that the projected growth in cross-river traffic will indeed materialise – or that people will wish to cross at this precise point, rather than further up, or down, river. A new bridge could prove an expensive white elephant and divert much-needed town resources away from other projects. The increased local taxes required could also scare the very businesses he is hoping to attract away to other local towns.

Option 1 – Waterfall

Waterfall, as a methodology, is all about building reliable systems. At each stage of the lifecycle, the results are correct. The Mayor’s engineer believes that - when building a bridge - the result needs to be safe, sound and capable of lasting for decades. He recommends a design phase, which includes thoroughly testing the bedrock by driving piles and developing ways to limit the future variance of the river’s course. During the build phase, the bridge would be tested to ensure it can take the loads that will be placed upon it and to deal with high winds or flood conditions. The engineer confirms that each stage would only start once the previous stage had been proved correct beyond reasonable doubt. The stone bridge will take five whole years to build (with a high upfront cost commitment). If the project were ever stopped, the value tied up in phases to date would be lost. The engineer reminds the Mayor that a collapsed bridge would not help his place in history!

Option 2 – RAD

RAD, as a methodology is all about building relevant systems. The argument runs that it is better to be there quickly with 80% of the functionality in 20% of the time, so as to take full advantage of the business opportunity. The Mayor’s political advisors recommend the RAD option; to lay a pontoon bridge first alongside the existing ferry. This can be achieved in just three months, using a series of boats with a makeshift road surface and swing bridge lock for river vessels to navigate. The pontoon bridge allows the business model to be tested very quickly; If the expected benefits materialise, then further iterations of the bridge can be constructed later on. Sounds good, - continued below ...