WBS Development

A WBS should be developed early to provide for a conceptual idea of program size and scope. As the program matures, so should the WBS. Like the technical baseline, the WBS should be considered a living document. Therefore, as the technical baseline becomes further defined over time, the WBS will also be updated to reflect more detail. For example, as specification requirements become better known and the statement of work is updated, the WBS will include more elements. As more elements are added to the WBS, the schedule is capable of greater definition, giving more insight into the program’s cost, schedule, and technical relationships. Elements of a WBS may vary by phase because different activities are required for development, production, operations, and support.

As the program or system matures, engineering efforts should focus on system-level performance requirements—validating critical technologies and processes and developing top-level specifications. As the specifications are further defined, the WBS will better define the system in terms of its specifications. After the system concept has been determined, major subsystems can be identified and lower-level functions determined, so that lower-level system elements can be defined, eventually completing the total system definition. The same WBS can be used throughout, updating and revising it as the program or system development proceeds and as the work in each phase progresses. One of the outputs of each phase is an updated WBS covering the succeeding phases.

It is important that each WBS be accompanied by a dictionary of the various WBS elements and their hierarchical relationships. In a WBS dictionary, each element is presented in an outline to show how it relates to the next higher element to ensure clear relationships. With minor changes and additions, the WBS dictionary can be converted into a statement of work. The dictionary may also be expanded by the program manager to describe the resources and processes necessary for producing each element in cost, technical, and schedule terms. Also, because the WBS is product oriented, it is closely related to and structured similarly to an indented bill of materials for the primary product. Like the WBS, the dictionary should be updated when changes occur. After the program is baselined, updating the WBS should be part of a formal process.