10.24 Project Work Breakdown Structure

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The Work Breakdown Structure (WBS) is a family-tree structure that relates to products produced and tasks performed at the various phases of the project life cycle. A WBS displays and defines the product(s) to be developed or produced and relates the elements of work (tasks) to be accomplished to each other and to the end product(s). Typically, three levels of WBS are developed during the system development process: Summary, Project, and Contract. A WBS Dictionary is also helpful for creating and recording the WBS elements.

10.24.1 Summary Work Breakdown Structure

The Summary WBS is a high-level WBS that covers the first three levels of the Project WBS. The Summary WBS is used for management presentations, but is not used for detailed day-to-day project management. The structure of the Summary WBS may vary depending on the nature of the project.

10.24.2 Project Work Breakdown Structure

The Project WBS is the detailed WBS that is used for day-to-day project management. The Project WBS includes all important products and work elements, or tasks, of the project, regardless of whether these tasks are performed by organizational personnel or by a contractor. The Project WBS may be modified, if necessary, during the life cycle. Work elements requiring more than two person-weeks of calendar time should be subdivided until the largest bottom-level work element represents work that can be accomplished in an interval of at least one person-week, but not more than two person-weeks. This subdivision may appear arbitrary, but the bottomlevel work elements should focus on finite tasks performed by a single individual. When that is done, the application of standard productivity rates can generally predict the expected duration of the work element and eliminate wide variation in work element duration.

For a software system development project, the structure of the Project WBS should also reflect the project life cycle approach. The structure of the Project WBS may vary depending on the nature of the project and should be customized by the Project Manager to reflect the particular project and the particular path through the life cycle. For example, a full-scale initial information systems development project and a software conversion process would be expected to have a much different WBS.

10.24.3 Contract Work Breakdown Structure

The Contract WBS (CWBS) is a further breakdown of the contract-specific WBS that covers the products and work elements, or tasks, from the Project WBS that will be performed by a contractor. In addition to items derived from the Project WBS, the CWBS includes contractor-specific items that may not be reflected in the Project WBS. Depending on the nature of the project, the contractor may be responsible for a given part of the project development activities (such as QA), for a specific part of the development life cycle (such as the Requirements Definition phase), or for the entire development process. A preliminary CWBS may be specified in the acquisition plan. The contract line items, configuration items, contract work statement tasks, contract specification, and contractor responses will typically be expressed in terms of the preliminary CWBS.

10.24.4 Work Breakdown Structure Dictionary

A WBS Dictionary provides detailed descriptions of each WBS element. Each WBS Dictionary entry should contain a title that is the same as the WBS element it amplifies, a narrative describing the work represented by the element, the effort required (in person-hours), the most likely duration (in calendar days), and references to any special skills or resources required to accomplish the work. WBS Dictionary entries should be completed only for the lowest-level WBS elements. Create one or more WBSs and a WBS Dictionary and it is possible to generate the output in the form of graphic charts.

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