The work breakdown structure
The work breakdown structure (WBS) provides the foundation for defining and organising the work needed to fulfil the project objectives.
It is a logical representation of all the work required to complete the project and offers an appropriate level of detailed analysis for planning and control. The WBS is a hierarchical deconstruction of the project into levels and sub-levels. It identifies work packages, which are the minimal elements of a WBS. Each WBS element has only one ‘parent’ and can be an activity, a more specific task, or even a part of the project output.
A work package can be used as the basis for planning, budgeting and monitoring the progress of a package. Each work package is a set of basic activities with clearly identified interactions with other work packages, and can be uniquely identified by its inputs, outputs and internal activities. In organisations, it is desirable to define a work package in such a way that only one organisational unit is responsible for its implementation (Globerson, 1994).
The WBS can be broken down according to the physical structure of the final outcome of the project, especially when it is a product, or a material artefact, such as a bridge. This type of WBS is also named ‘product breakdown structure’ because it resembles the list of materials which compose the final product, as in the following example:
WBS by product breakdown structure
Alternatively, a WBS can be based on the different phases of the project, independently from the level of decomposition of the final output, such as in the following example:
WBS by phases of the project
Clearly, there are varying levels of detail into which a WBS can be broken down. The choice of the extent to which activities are broken down into smaller components is defined by the need to identify the list of clear outcomes for which the project participants can be held responsible and which can be associated with a final evaluation of the results (in terms of time, cost and quality).
Each element in a WBS should be labelled with a unique identifier to allow for a better management report of costs and resources. The numbering should follow a coding scheme which clearly represents a hierarchical structure. This is illustrated in the examples above which show two ways of defining the content of a WBS.
It is important to note that many projects actually mix the two approaches, combining phases and parts of the project outcomes at different levels of the WBS. This is a realistic response to the need to capture the complexity of a project at the planning stage. In the example of the book, the writing stage (1.2) is divided in sublevels according to the structure of the book, and not on the basis of the writing stages, because that was the most logical way to approach the planning of the writing activity.
According to Horine (2012), a well-done WBS should:
- Break the project down into smaller units with milestones to demonstrate progress, rather than working on the whole project in one go
- Identify all necessary work for the project and only the necessary work
- Facilitate accurate cost, duration and resource estimates based on single work packages
- Similarly, focus control on single work packages
- Define clear responsibility at both an individual and organisational level, giving participants more autonomy and facilitating the integration of different workers
- Ensure stakeholders and participants understand and buy into the project’s scope and see how their activities or support contribute to its achievement
- Support the identification of risk factors through breaking down the work.
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