Thursday, November 13, 2003

Chapter 4 - Dealing with Uncertainty

Chapter 4 introduces a critical theme in the book - uncertainty. It shows how to analyze uncertainty in the 3 key constraints of software development - scope, schedule and resources. There is much greater uncertainty in scope, and considerably less in resources and very little in desired delivery date. Often so much is dependent on a delivery date - a whole marketing and distribution program - that a date cannot slip. Hence, it is certain that the date must be hit. The resources for a project are generally fairly fixed and difficult to vary at short notice. As Fred Brooks said, “adding people to a late project makes it later”. The scope, however, does generally have a lot of uncertainty attached to it. Requirements do change and scope does creep.

Rather than classify uncertainty into Deming’s traditional 2 types of variation - common cause and special cause - a newer approach is taken where uncertainty is classified into 4 types - common cause variation, foreseen uncertainty, unforeseen uncertainty and chaos.

Buffering for uncertainty is examined and the “local safety” problem are introduced. The chapter ends with an explanation of how to reduce uncertainty through aggregation of tasks with the resultant buffering being calculated as the square root of the sum of the squares of buffers for each task.

The Agile Manager must learn to accept uncertainty is real and through acceptance master it with judicious use of buffers.