A work breakdown structure, or WBS, is a tool used by those in the field of project management. It is used to define a project and separate each of the project's elements into defined group entities so that they can be assigned and completed in a more efficient manner. The elements could include products in a sales oriented project, components in a building project, or delegation of authority in a management project.
In a work breakdown structure, elements are defined and then broken down into a tree system. This system gives each part of the project a different priority and matches that level of importance to its place on the tree. The tree also serves to delegate the various parts of the project to the various workers who are assigned to complete it. By doing this, confusion is eliminated. Additionally, the project manager may wish to assign due dates for each of the project pieces, based on the amount of time it should take the workers to complete it. Each piece of the tree may be divided into smaller work breakdown structures by the employees assigned that particular piece of the project.
The work breakdown structure originated with the military. The U.S. Department of Defense created the concept when developing the Polaris missile program in the late 1950s. After completing the project, the DOD published the work breakdown structure it used, and mandated that this procedure be followed in future projects of this scope and size. Subsequently, this method of project management has been absorbed into the private sector and remains one of the most common and effective ways in which corporate projects are completed.
In order to make the work breakdown structure as efficient as possible, there are several rules that are typically followed in the development of the tree. The first of these is the 100% rule. This states that the breakdown structure should include 100% of the goal-oriented work required by the project. As an aside to this, however, a work breakdown structure should focus only on the outcomes of a project, and not the methods of bringing the project to fruition. Additionally, the structure should strive to include only mutually exclusive elements in the tree. This prevents overlap and ensures that everyone knows their assigned tasks.
A work breakdown structure is not a total listing of all the work that will go into a project. It is simply a tree to enable efficient delegation of the responsibilities and man hours that should be put into the project. Also, a work breakdown structure is not to be used for purposes of personnel organization. The scope of the project should be outlined in such a way that employee delegation can flow from the tree, rather than be defined by the tree itself. A separate organizational hierarchy chart may be used to define each groups responsibility within the breakdown structure.
Many companies and project managers find themselves overwhelmed by a work breakdown structure because they go overboard on the level of detail required by the structure. This is why it is important to keep the WBS as simple as possible. Included within this admonishment is the importance of adhering to the 80 hour rule. This means that no element of the project should exceed 80 hours of work per person assigned to the project. This is a decent rule of thumb to assist the project manager in knowing where and when to break a project element down into two or more sub-elements.