CHAPTER 2 Deliverable-Oriented Work Breakdown Structure

A work breakdown structure (WBS) provides a framework of common reference for all project elements, specific tasks within the project, and ultimately better schedules and better estimates. A WBS facilitates the integration of project plans for time, resources, and quality. An effective WBS encourages a systematic planning process, reduces the possibility of omission of key project elements, and simplifies the project by dividing it into manageable units. If the WBS is used as the common skeleton for the schedule and the estimate, it facilitates communication among the professionals implementing the project.

Before addressing the WBS, it is useful to set the proper perspective for project structures. Three separate structures need to be created, defined, or modified for the purposes of a project: (1) the organizational breakdown structure (OBS), (2) the resource breakdown structure (RBS), and (3) the WBS.

The OBS is the most readily available structure. Since companies frequently go through massive organizational changes, it is necessary to use the most current data with frequent updates as changes occur to the reporting lines of the organization. For the purposes of the project management system, the organizational chart must be augmented by unwritten responsibilities and by dotted-line relationships that affect the execution of the project.

The RBS is a logical and useful classification of the resources necessary to accomplish the project objectives. Rather than developing a new RBS for each project, it is more efficient to develop an RBS for a large family of projects. As each new project is planned, only those portions of this common RBS that apply to the project will be selected and used. A project RBS is different from all other human resource or budgeting classification methods in that it reflects applicability to project management as compared to cost accounting or to personnel evaluations. An RBS is essentially a catalog of all the resources that are available to the project. RBS development will be discussed in Chapter 3.

The most difficult to define, and yet the most useful of these three project structures, is the WBS. Its information is drawn primarily from the project objectives statement, historical files of past projects, project performance reports, or any other files containing the original and final project objectives of previous projects. As with the RBS, sometimes it is appropriate to develop a general WBS for a family of projects, and then for each project only the appropriate segments need to be selected and modified. This practice is appropriate in organizations that conduct projects that are somewhat similar albeit not identical.