figure 1: PDCA cycle

Rapid and frequent feedback

If everything would be completely clear we could use the waterfall development model. We call this 'production' rather than 'development'. At the start of a new development, however, there are many uncertainties we have to explore, and change into certainties. Because even the simplest development project is too complex for a human mind to oversee completely (E. Dijkstra, 1965: "The competent programmer is fully aware of the limited size of his own skull"1) we must iteratively learn what we are actually dealing with and learn how to perform better.

This is done by "think first, then do", because thinking costs less than doing. But, because we cannot foresee everything and we have to assume a lot, we constantly have to check whether our thoughts and assumptions were correct. This is called feedback: we plan something, we do it as well as we can, then we check whether the effects are correct. Depending on this analysis, we may change our ways and assumptions. Shewhart2 already described this in 1939. Deming3 called it the Shewhart Cycle. Others call it the Deming cycle or PDCA (Plan-Do-Check-Act) cycle, see figure1.

In practice we see that if developers Do something, they sometimes Plan, but hardly ever explicitly go through the analysis (Check) and decision (Act) sections. In Evo we do use all the sections of the cycle deliberately, in rapid and frequent feedback loops (figure 2):

figure 2: Planning cycles

The weekly TaskCycle
In this cycle we optimise our estimation, planning and tracking abilities in order to better predict the future. We check constantly whether we are doing the right things in the right order to the right level of detail for the moment.

The frequent stakeholder value DeliveryCycle
In this cycle we check our assumptions and optimise the requirements. We check constantly whether we are delivering the right things in the right order to the right level of detail for the moment. Delivery cycles take 1 to 2 weekly cycles.

The strategic objectives cycle
In this cycle we review our strategic objectives and check whether what we do still complies with the objectives. This cycle may take 1 to 3 months.

The organisation roadmap cycle
In this cycle we review our roadmap and check whether our strategic objectives still comply with what we should do in this world. This cycle may take 3 to 6 months.

  1. E. Dijkstra: Paper: Programming Considered as a Human Activity, 1965. Reprint in Classics in Software Engineering. Yourdon Press, 1979, ISBN 0917072146.
  2. W. A. Shewhart: Statistical Method from the Viewpoint of Quality Control. Dover Publications, republication: 1986. ISBN 0486652327.
  3. W.E. Deming: Out of the Crisis. MIT, 1986, ISBN 0911379010.