What is a work breakdown structure (WBS)?

Once we have identified all of the things that we are supposed to produce in the project, it is necessary to develop the specific items of work that must be done to complete all of the work. The work breakdown structure takes the project and divides it into smaller pieces. These can be called subprojects. The subprojects can be broken down into smaller pieces. This process of breaking down the project can continue until the project is broken into small, more manageable pieces.

The work breakdown structure allows us to approach the formidable task of finding all of the work that is necessary for completion of the project. This is done by taking the formidable project and dividing it into small projects that can be looked at one by one, allowing the project to be attacked one piece at a time. When the work breakdown structure is not used, it is very likely that many of the tasks will be missed. Since this is the place in the project where the work is defined, we find the work breakdown structure useful in determining much of the information we will require in our project plans.

To make work breakdown structures even easier, they are not restricted to only dealing with work. Many work breakdown structures start out as product breakdown structures. That is, the first few levels of the WBS are the breakdown of the products of the project from major products into smaller subproducts. For large projects this frequently makes the construction of the WBS much easier. If, for example, you were to consider the construction of the U.S. space shuttle, you would first see a product breakdown followed by a work breakdown.

Some of the major components of the space shuttle program were construction of the launch facility, construction of the space shuttle vehicle, construction of the solid rocket boosters, construction of the external fuel tank, modification of the world tracking stations, modification of the astronaut training facility, development of new space suits, and development and construction of the robot arm assembly.

The space shuttle program had several layers of product breakdown before the WBS considered actual work packages, tasks, and activities. In huge projects like this, the individual products are so large in themselves that there might be little interaction between team members working on widely separated branches of the project. People working on the external fuel tank had relatively little contact with the people working on the tracking stations around the world.

The work breakdown structure is a simple, easy-to-read, graphical representation of the project that is very useful for communicating to the stakeholders of the project.

The work breakdown structure provides us with the basis for performing the bottoms-up cost and schedule estimate for the project as well. Since the WBS represents all of the work that must be done to complete the project, we can estimate the cost and duration for each of these small pieces of work and roll the estimate up to the project level for the total cost and duration estimate.

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The work breakdown structure is one of the most useful tools in project management. It is easy to use and simple to understand. Essentially, the project is first taken as a whole and broken down into a small group of subprojects. These subprojects can each be broken down into subsubprojects. These can be broken down further until very small pieces of the project can be described.

This breaking down of the project has some major advantages. The main advantage is that it allows us to concentrate our efforts on small parts of the project one piece at a time. If we were to try to determine at once all of the work necessary to complete a project, we would probably do a good job in some areas and a not very good job in other areas. By breaking the project into successively smaller subprojects, we can organize groups of people to concentrate on finding the work associated with one, and only one, part of the project at a time and do a thorough job, with only the appropriate people for that part of the project.

The WBS is one of the tools in project management that allows us to manage any size project. A very large project can be broken down through many levels of the WBS until an element of a manageable size is achieved. In a smaller project, the same manageable element can be achieved with fewer levels of breakdown. In this way even the largest project can be broken down into a small manageable subproject (see Figure 2-8).

Figure 2-8: PMI WBS DEFINITIONS

So, the top level of any WBS is the project that we are concerned with. The levels between the top and bottom of the WBS are elements of breakdown. The larger the project, the more levels of intermediate breakdown we have. Eventually we come to the bottom of the WBS. This is the smallest level of detail that the project manager will have to manage. The Guide to the Project Management Body of Knowledge is a little bit confusing in this area. It says that the WBS should continue only to the work package level since this is the lowest level to which the project manager will have to manage. It goes on to say that the work packages can be broken down into activities and the activities can be further broken down into tasks.

Most project managers will construct a WBS that is appropriate to their project. Even if a very large project is being managed, the entire WBS will actually contain all the work associated with the project, and the project manager will be responsible for it all. In very large projects there will be intermediate managers. They may even be called work package managers. These intermediate managers may have their own responsibilities, but the project manager they report to is still responsible for their work as he is responsible for all aspects of the project. So, in our way of thinking, the WBS contains all of the work involved in the project. If the project is large and the project manager wants to display the WBS only down to the work package level, that is fine. The complete WBS, however, goes down to the level of detail that can be assigned to an individual person. In this way the project manager and the intermediate managers can each construct their part of the WBS, and the pieces will fit together into an overall project WBS. This will, in turn, support the planning process for the project in a consistent way.

The work breakdown structure also has the capability of including the non-task-related work. This is the work that is considered to be "level of effort" work. The best example of this is the project manager. There are other cases, especially when projects become large, where other level of effort persons are involved. Level of effort work is the work that must be done in the project, but it is work that is not connected to any one task in particular. Level of effort work is work that affects many of the activities of the project. For example, a person that is responsible for operating the copy machine used by everyone in the project is a level of effort person. Administrative assistants and anyone else who does work that contributes to the project but does not work on any specific task is a level of effort person. A major attempt should be made to avoid calling work level of effort when it should really be assigned to a particular task. Level of effort work is budgeted but is difficult to measure in terms of performance. Level of effort people and their work can be shown in the WBS at the level at which they do their work.

The WBS must be a flexible tool that can be used with as little restriction as possible so that it will be used with ease and comfort. Since each project is unique, the requirements of the project will change each time, and the WBS must be able to be used in all circumstances.

You may have noticed that we have been careful so far to avoid some of the usual words that are associated with the work breakdown structure. This is because there is some disagreement about what exactly should go into the WBS. As recently as April 2000, PMI published "Work Breakdown Structure Practice Standard Project—WBS vs. Activities" by Cindy Berg, PMP, and Kim Colenso, PMP, in the PM Network.

This paper addressed the disagreement between project managers as to whether it was appropriate for the WBS to contain the project activities. One opinion is that it is not appropriate for the WBS to contain the project activities because the level of planning in the WBS is only to the deliverable level and does not go to the level of the individual assignment. It is therefore inappropriate for the WBS to contain the project activities. The opposite view is that the WBS should contain the project activities. This is appropriate because the lowest level of the WBS contains elements that in fact produce the deliverables of the project. In this opinion, the process of creating the deliverables leads us to the definition of the work that is required to produce them.

We think that the paper correctly states that it is really up to the project manager to construct the WBS in a way that is appropriate for the project. All projects are different, and the WBS is a tool that should be used in a manner that is appropriate for each project encountered. It would be inappropriate for PMI to place restrictions on their options. The WBS is a project management tool that can be used in different ways, depending upon the needs of the project manager. Therefore, there should not be arbitrary limits set on how the WBS should be created.