Application and Use of the WBS
The use of the WBS for scope management goes well beyond its use as a framework through which the required work effort may be assigned to deliverable items. It serves also to portray and trace the family relationships among functional components of the configuration. The hierarchical breakdown reflects the progressing design of the end product. Military Standard 881A specifically calls for the WBS to be used in this fashion.
So that it may serve as the information framework for configuration management purposes, Military Standard 88lA requires that certain elements in the WBS be designated as configuration items meaning devices or components that are to be developed or manufactured through the project to satisfy specified end use functions. A configuration item is the object of design activity during the project. In response to a specified operational need, first a set of performance parameters is determined for an item and then a hardware and software configuration is conceived. As the design work progresses, the WBS is successively extended to lower levels, reflecting the designer's choices of the sub-components and sub-subcomponents within an item.
The designation of certain WBS elements as configuration items does not restrict the use of other elements for management purposes. Integration of components, testing, project administration, and training, for example, are all accommodated in the WBS. For these kinds of elements, the degree of breakdown may be less than for configuration items. The overriding requirement remains, however, that for each element there must be certifiable outputs or deliverables, be they documents, services, or physical items.
One of the earliest reported uses of the WBS for scope management and configuration planning is Allen's description of the application of a master code (identical in concept to a WBS) on a large construction project. For the design and construction of a multi building mechanized postal sorting plant, the upper levels of the code structure were implemented at an early stage. Each summary level element had well defined physical boundaries and contained specific structural, architectural, or process components. As more detail on design and procurement choices became available, the structure was expanded to lower levels. In the case of building construction, the lowest level elements were individual contract (trade) packages, each with a defined scope and a separately prepared set of drawings and specifications.
Allen presents, as an illustrative example, a contract package whose end product was the erected structural steel for one of three physical areas in a building. The detailed design and construction specifications were prepared as separate undertakings for each of the three contract packages in this family group. At the time of funding authorization, a scope statement was written at one level of summarization higher: for all of the structural steel in the building. Companion funding packages were for steel decking and for miscellaneous steel. The three funding packages, in turn, summarized into building steel as an element distinguished from foundations, the enclosure, mechanical systems, and electrical systems for instance. It was only subsequent to funding authorization that scope components were subdivided to establish contract packages, each corresponding to a clearly demarcated physical area, system, or component within the plant.
The act of subdivision should never change the scope of an element or configuration item; it merely expands the detail through elaboration. In the next section, the use of the WBS as a control tool for configuration management will be further illustrated. The structure traces out an audit trail and a set of baseline standards whereby it can be verified that the authorized project scope is neither increased nor diminished in the course of designing and producing the end item.
In Part 3, Walter Wawruck will provide a Framework
for Controlling Scope.
States Department of Defense. Work Breakdown Structures for Defense Materiel Items
MIL STD 881A. Washington, D.C.: Department of Defense, 25 April, 1975, pp3-16
60. Ibid, p12
61. Allen, W.E. The Master Code: Its Application on the Large
Construction Project. Proceedings of the 1973 Seminar Symposium Drexel Hill, PA:
The Project Management Institute, 1973, p678