A complex project is made managable by first breaking it down into individual components in a hierarchical structure, known as the work breakdown structure, or the WBS. Such a structure defines tasks that can be completed independently of other tasks, facilitating resource allocation, assignment of responsibilities, and measurement and control of the project.
The work breakdown structure can be illustrated in a block diagram:
Work Breakdown Structure Diagram
Terminology for Different Levels
Each organization uses its own terminology for classifying WBS components according to their level in the hierarchy. For example, some organizations refer to different levels as tasks, sub-tasks, and work packages, as shown in the above outline. Others use the terms phases, entries, and activities.
Organization by Deliverables or Phases
The WBS may be organized around deliverables or phases of the project life cycle. Higher levels in the structure generally are performed by groups. The lowest level in the hierarchy often comprises activities performed by individuals, though a WBS that emphasizes deliverables does not necessarily specify activities.
Level of Detail
The breaking down of a project into its component parts facilitates resource allocation and the assignment of individual responsibilities. Care should be taken to use a proper level of detail when creating the WBS. On the one extreme, a very high level of detail is likely to result in micro-management. On the other extreme, the tasks may become too large to manage effectively. Defining tasks so that their duration is between several days and a few months works well for most projects.
WBS's Role in Project Planning
The work breakdown structure is the foundation of project planning. It is developed before dependencies are identified and activity durations are estimated. The WBS can be used to identify the tasks in the CPM and PERT project planning models.
