A Work Breakdown Structure (WBS) is a fundamental project management technique for defining and organising the total scope of a project, using a hierarchical tree structure. The first level defines the planned objectives of the project. At each subsequent level, the children nodes collectively represent 100% of the scope of their parent node. The WBS is commonly used to identify the major outcomes (level one and two) to be accomplished in the project. It can be drilled down further to outline the detailed tasks associated with those outcomes.
- The 100% Rule is the key design principle for WBS. The rule states that the WBS includes 100% of the work defined by the project scope and captures all deliverables. This rule applies at all levels within the structure. The rule ensures that activities required to complete the project are included and excludes any work that falls outside the actual scope of the project.
- A WBS is not an exhaustive list of work. A good WBS describes outcomes of the project rather than the actions, as the former is easier to predict.
- The components of the WBS should be mutually exclusive. This is to ensure that there is no overlap in the scope of any components as ambiguity could result in duplicated work or miscommunications about responsibilities.
- An appropriate level for a WBS component is one that:
- Effort can be realistically estimated
- Cannot be logically subdivided further
- Completed in a reasonable amount of time
- Have a meaningful outcome
- Can be completed without further dependencies
- A good WBS should be well balanced in its breadth and depth. This requires proper grouping and structuring of components. A common rule-of-thumb is to avoid having more than 7 immediate sub-elements below any given node of the WBS.