Chapter 5. Using the Work Breakdown Structure to Plan a Project

In a previous chapter, I said that planning answers the questions “What must be done?,” “How long will it take?,” and “How much will it cost?” Planning the what is vital; projects frequently fail because a significant part of the work is forgotten. In addition, once tasks have been identified, the time and resource requirements must be determined. This is called estimating.

A major problem in project planning is determining how long tasks will take and what it will cost to do them. Inaccurate estimates are a leading cause of project failures, and missed cost targets are a common cause of stress and recrimination in project management.

The most useful tool for accomplishing all of these tasks is the Work Breakdown Structure (WBS). The idea behind the WBS is simple: You can subdivide a complicated task into smaller tasks, until you reach a level that cannot be further subdivided. At that point, it is usually easier to estimate how long the small task will take and how much it will cost to perform than it would have been to estimate these factors for the higher levels.

Nevertheless, it is still not easy to estimate task durations for activities that have never been performed before. Because this is the typical situation in engineering hardware and software development projects, we might expect many of these estimates to be in error, and this seems to be demonstrated by experience. Still, the Work Breakdown Structure makes it easier to estimate knowledge tasks than any other tool we have.