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CHAPTER 4Using the Work Breakdown Structure to Plan a Project

Planning answers the questions “What must be done?,” “How long will it take?,” and “How much will it cost?” Planning the “What” is vital; projects frequently fail because a significant part of the work is forgotten. In addition, once tasks have been identified, the time and resource requirements must be determined. This is called estimating.

A major problem in project planning is determining how long tasks will take and what it will cost to do them. Inaccurate estimates are a leading cause of project failures, and missed cost targets are a common cause of stress and recrimination in project management.

The most useful tool for accomplishing all of these tasks is the Work Breakdown Structure (WBS). The idea behind the WBS is simple: you can subdivide a complicated task into smaller tasks, until you reach a level that cannot be further subdivided. Decomposition is used in developing the WBS. A that point, it is usually easier to estimate how long the small task will take and how much it will cost to perform than it would have been to estimate these factors at higher levels.

Nevertheless, it is still no easy feat to estimate task durations for activities that have never been performed before. Because this is the typical situation in engineering hardware and software development projects, we might expect many of these estimates to be in error, and this seems to be demonstrated by experience. Still, the Work Breakdown Structure makes it easier to estimate knowledge tasks than any other tool we have.

A Simple Example

As an example, if I want to clean a room (see Exhibit 7), I might begin by picking up clothes, toys, and other things that have been dropped on the floor. I could use a vacuum cleaner to get dirt out of the carpet. I might wash the windows and wipe down the walls, then dust the furniture. All of these activities are subtasks performed to clean the room.

As for vacuuming the room, you might have to get the vacuum cleaner out of the closet, connect the hose, plug it in, push the vacuum cleaner around the room, empty the bag, and put the machine back in the closet. These are still smaller tasks to be performed in accomplishing the subtask called vacuuming. The diagram in Exhibit 7 shows how this might be portrayed in WBS format.

Exhibit 7: WBS Diagram to Clean a Room

Note that we do not worry about the sequence in which work is performed when we do a WBS. That will be worked out when we develop a schedule. However, you will probably find yourself thinking sequentially, as it seems to be human nature to do so. The main idea of doing a WBS is to capture all of the tasks. So if you mind yourself and other members of your team thinking sequentially, don’t be too concerned, but don’t get hung up on trying to diagram the sequence or you will slow down the process of task identification.

The typical WBS has three to six levels, and these can be labeled as shown in Exhibit 8. It is, of course, possible to have projects that require a lot more levels. Twenty levels is considered to be the upper limit, and that is a huge project. Note that level 1 is called the program level. The difference between a program and a project is just one of degree.

Exhibit 8: WBS Level Names

An example of a program is the development of an airplane. For example, the WBS for Boeing’s 787 airplane program might have been drawn as shown in Exhibit 9. Notice that the engine, wing, and avionics are large enough jobs to be called projects in their own right. In fact, the program manager’s job is to make sure that the projects are all properly integrated. The engine mounts on the wing, so, somewhere in the structure to develop the engine, there will be an activity called “Design wing mounts.” And for the wing, there will be an activity called “Design engine mounts.” If these are not coordinated properly, you will wind up with an engine that won’t mount on the wing. The job of coordinating these is called system integration.

Exhibit 9 : Partial WBS for the 787 Development Program

Guidelines for Developing the WBS

One important question in constructing a WBS is “When do you stop breaking down the work?” The general guideline is that you stop when you reach a point where either you can estimate time and cost to the desired degree of accuracy or the work will take an amount of time equal to the smallest units you want to schedule. If, for instance, you want to schedule to the nearest day, you break down the work to the point where tasks take about a day to perform. If you are going to schedule to the nearest hour, then you stop when task durations are in that range.

Remember the rule that the people who must do the work should participate in planning it? That applies here. Usually a core group identifies top-level parts of the WBS; those parts are further refined by other members of the team and then integrated to obtain the entire WBS.

One important point: the WBS should be developed before the schedule. In fact, the WBS is the device that ties the entire project together. It allows resources to be assigned and estimates of time and cost to be made and shows the scope of the job in graphic form. Later, as the project is tracked, the work can be identified as falling in a particular box in the WBS.

There are many software packages that print a WBS after schedule data have been entered. That is a nice feature, since it gives a graphically attractive WBS. It is important that the rough drawing be made prior to input in the scheduling software, though. The reason is quite simple: until everyone has agreed that all tasks have been identified, it is misleading to develop a schedule. You cannot be sure that the critical path identified by a partial schedule will be the same for the full schedule.

There are a number of approaches to developing the WBS. Ideally, you proceed top-down, following development of a good problem statement and mission statement. As previously mentioned, however, the mind does not always operate in such nice, linear fashion. As you develop the WBS, you may sometimes find that it helps to understand the job better. For that reason, about it is not necessary to be so strict about doing things in a specific order. You do what works best for you.

The WBS does not have to be symmetrical. That is, all paths need not be broken down to level 6 (or whatever level you stop at). Since the rule is to break work down to a level sufficient to achieve the estimating accuracy you desire, one path may take six levels, while another may need only three.

Uses of the WBS

The WBS is a good way to show the scope of a job. If you have ever given someone an estimate for project cost or time and seen the person’s horrified look, you know that they are seeing the project in their mind as much simpler than it is. When you show a project in WBS for, it is clear to most individuals why the job costs so much. In fact, we see the experience of the planning group members themselves being overwhelmed by the complexity and magnitude of the WBS. If it impresses them, think of the impact on the outsider.

Assigning responsibility for tasks is another important use of the WBS. Each task to be performed should be assigned to a particular person who will be responsible for its completion. These assignments can then be listed on a separate form, often called a responsibility chart (see Exhibit 10).

Exhibit 10: Responsibility Chart

Estimating Time, Costs, and Resources

Once the work is broken down, you can estimate how long it will take. But how? Suppose you ask how long it will take to sort a thoroughly shuffled standard deck of playing cards into numerical order by suit. How would you answer that question?

The most obvious way would be to try the task several times and get a felling for it. But if you didn’t have a deck of cards handy, you would probably think about it, imagine how long it would take, and give an answer. People generally give answers ranging from two minutes to ten minutes. Tests indicate that about three minutes is average for most adults.

Suppose, however, the same task was given to a child about four or five years old. It might take a lot longer, since the child would not be that familiar with the sequence in which cards are ordered, and perhaps not yet even be that comfortable with counting. This leads to a very important conclusion: you cannot do a time or cost estimate without considering who will actually perform the task. Also, you must base the estimate on historical data or a mental model. Historical data are best.

Generally average times are used to plan projects. That is, if it takes three minutes on average for an adult to sort a deck of cards, three minutes would be a good estimate to use of how long it will take during execution of my project. Naturally, when using averages, some tasks will take longer than the time allowed and some will take less. Ultimately, however, they should all average out.

That is the idea, anyway. Parkinson’s Law discredits this notion, however. Parkinson said that work always expands to fill the time allowed. That means that tasks may take longer than the estimated time, but they almost never take less. One reason is that when people find themselves with some time left, they tend to refine what they have done. Another is that people fear that if they turn work in early, they may be expected to do the task faster the next time or that they may be given more work to do.