PBS or WBS?

This article provides participants in the Project Management Concepts course with an understanding of the rationale behind breakdown structures in Project Management, and the difference between a PBS and a WBS.

Introduction

Why is there confusion between different types of breakdown structures?

Way back in 2009, Simon Harris wrote an article explaining why breakdown structures are so important to managing projects safely.

Simon Harris is a member of several professional organisations and a thought leader on Project Management. As a PMP^® credential holder and former PRINCE2^® examiner, Simon complained that the standards authorities themselves are to blame for the frequent confusion between the purpose of the different kinds of breakdown structures. The people who wrote the guidelines were obviously not clear in their own thinking!

So, what works in the real world of Project Management?

Simon’s real-world advice about breakdown structures is line with the idea that a successful project is a project that achieves its purpose. It makes sense, therefore, that when you plan, you should begin with the end in mind. In other words, you should be clear about the goal of the project, because everything you do after that should be fit for that purpose.

Planning steps

The basic thinking steps when planning a project are:

1. Think first about what you want to achieve (the goal, or purpose).
2. Then think about what you might produce to achieve that (the end product, or deliverable).
3. Finally, think about what work (tasks, or activities) should be done to produce that product.

After that, you can put the activities into a sequence, assign people to do the work, and so on. (In other words, don’t start a project plan by making a Gantt chart! That only comes after step 3!)

The example below illustrates the steps in a simple way.

Example

DCI’s branch office used to be a residential home, and it still looks like one. Customers and suppliers often drive right past the place, and they seem a bit cross when they finally arrive there, having phoned again for directions. DCI’s branch manager would like to ensure that the branch presents itself in a more respectable, businesslike manner.

That’s the goal of the project.

After chatting to a few customers, the guys in the branch office decide that a small wall next to the street, bearing the company logo, would be fit for this purpose.

That’s the product.

PBS (Product Breakdown Structure)

The office administrator does a quick Product Breakdown Structure, identifying some of the sub-products which must be produced by the project, and shows it to the others.

The branch manager reckoned it would be elegant to have a light below the wall capping to illuminate the sign at night, but the receptionist would prefer not to have to remember to put on the silly light when she leaves at five, so she points out that no-one comes to the office at night anyway, so a light would be an overkill and a waste of electricity. The light is therefore taken out of the scope of the project.

WBS (Work Breakdown Structure)

The office administrator then starts to identify the tasks which would have to be done to produce those sub-products.

She does this by creating a Work Breakdown Structure. She doesn’t know what tasks are involved with designing a wall or a sign, and nor do her colleagues, so she doesn’t try to break down that task further yet.

Business case

The business case seems to be approved already, because everyone thinks it’s a good idea! However, the office administrator still needs to check whether the time and money and attention that this project would require would be justified, given all their other priorities at the office. Instead of just getting straight down into the details of the work tasks, she therefore decides to spend a few hours getting a broad idea of the costs and the time that it would take so that she can put together a short, formal business case to be signed off before going ahead with the project.

A note about standards

The PMBOK® Guide

A Guide to the Project Management Body of Knowledge (also known as the PMBOK^® Guide) is a standard for Project Management published by the PMI®. According to this standard, creating a WBS is a formal process. The sequence of processes in the PMBOK^® Guide is different from the simple three steps described in the example above. According to the PMBOK^® Guide, the development of a Business Case isn’t actually part of the processes of Project Management at all—the Business Case must be signed off long before the project manager gets people together to work on the WBS.

However, if we understand what a WBS seeks to provide, we can see why it can be very useful to do at least a high-level WBS before embarking on a project, as in the example above.

PRINCE2®

In PRINCE2®, the project manager must ensure that the Business Case satisfies all the requirements needed to manage the project going forward. This happens at the beginning of the project.

PRINCE2® incorporates Product Based Planning, a detailed technique which follows the rationale behind the three steps described in the example above.