Building Effective Work Breakdown Structures (WBS)

Main WBS components

Figure 2: WBS example and components ^[1]

The focus of this section is to explain the main WBS components. This example was taken from the Practice Standard for Work Breakdown Structures by the Project Management Institute (PMI). Figure 3 was selected for simplicity in illustrating the product, and the intention is to allow the reader to focus on the WBS and its essential components. ^[1]

The main components of a WBS will be explained using figure 1 as a reference:

• Levels and WBS IDS:

Level 1: Regardless of the type of decomposition or the style of the WBS, the first level always represents the name of the project, product, or initiative. This level includes the entire scope of work necessary to produce the product, service, or outcome of the project designated by the number 1. In figure 2, the “bicycle” represents the product of the project ^{[1] [5]}.

Level 2: This is the first level of decomposition for the project which provides a high-level view of the scope of the project. The numbering in the second level is 1.1, 1.2, 1.3,…., 1,n. In the example of the bicycle, the second level represents all the components required to deliver the final product ^{[1] [5]}.

Level 3 and below: These levels decompose further the deliverables from Level 2. These levels correspond to only one parent in level 2 and the numbering is: 1.1.1, 1.1.2, 1.1.3, …, 1.1.n, 1.2.1, 1.2.2, 1.2.3, …, 1.2.n, according to the needs of the project ^{[1] [5]}.

• Work Packages:

As introduced in section 1.1, a work package is defined as the lowest level in a WBS which represent tasks that can be assigned to a team member or department. For project managers, this level of detail will allow to reliably estimate cost, duration, and to monitor and control the work ^{[1] [5]}.

Building effective WBS

Preparation methods

There are different methods and tools available to create a WBS such as top-down and bottom-up development strategies, WBS organizational standards, WBS templates, brainstorming, expert assistance, and mind mapping, among others. The selected method depends on the project objectives, requirements, assumptions, and constraints ^[5]. This article will focus on explaining the top-down and bottom-up approaches as they are often referred to in the literature about WBS.

Top-down method

This is one of the most preferred methods when creating a WBS. The decomposition process starts at the top of the WBS. In other words, you begin with the overall picture and continue breaking down the work into smaller, more manageable components ^[5]. The following steps describe the general approach for developing a WBS following the top-down method:

Figure 2: Top-down approach ^[5].

Step 1: Identify all the final products, services, or outcomes that the project will deliver. They are the level 2 components ^{[1] [5]}.

Step 2: Define major interim deliverables to accomplish each level 2 components ^{[1] [5]}.

Step 3:Break down each major deliverable to a level of detail that allows appropriate management and control. Following the 100% rule, the total of elements at each level represents 100% of the necessary work for the above element ^{[1] [5]}. Section 4.2.1 will present a decomposition technique for the project work.

Step 4:Review and validate with key stakeholders until agreed that the project planning can be successfully completed and that the execution will produce the required deliverables and results ^{[1] [5]}.

Bottom-up method

This method starts at the lowest level of deliverables – the work packages – and works upwards to the top level of the WBS ^[5]. The following steps describe the general approach for developing a WBS following the bottom method:

Figure 3: Bottom-up approach ^[5].

Step 1: Identify all the work packages of the project (deliverables), each work package typically contains one deliverable ^{[1] [5]}.

Step 2:Group related work packages logically ^{[1] [5]}.

Step 3:Aggregate deliverables to the next parent level. Following the 100% rule, the sum of elements at each level represents 100% of the work required below it ^{[1] [5]}.

Step 4:Once a specific set of interconnected work packages has been consolidated into a parent element, re-examine the subset to make sure that all the work has been included ^{[1] [5]}.

Step 5:Repeat until all the work packages have been aggregated to a single parent, level 1 element of the WBS, and make sure that the completed structure encompasses the entire scope. ^{[1] [5]}.

Step 6:Review and validate with key stakeholders until agreed that the project planning can be successfully completed and that the execution will produce the required deliverables and results ^{[1] [5]}.

Decomposing the project work

How to decompose the project work?

The decomposition technique is used when creating a WBS to break down the project. This is an iterative process that starts by identifying the best approach, according to section 3.2, to decompose the major deliverables. Figure 5 shows the iterative nature of the work decomposition until all the work packages are identified. When breaking down the scope of the project, you should consider the question: Is this work package detailed enough to be effectively estimated and managed, or should it be broken down further for better comprehension and management? ^[5].

Figure 4: Decomposition technique diagram ^[5].

When to stop decomposing the work?

Various guidelines for determining when to stop the decomposition process are based on the amount of time that takes to complete a work package ^[5]. An example of this rule is given by Dr. Harold Kerzner: "A typical work package may be 200–300 hours and approximately two weeks in duration"^[2]. A practical tip given by Liliana Buchtik is to decompose to the level of detail for which you are able to manage, assign the work, and estimate cost and time ^[5].

WBS Dictionary

The WBS dictionary is a document that supports the WBS by providing comprehensive information for each element within it. The information in the WBS dictionary typically includes a detailed description of the work, deliverables, and milestones associated with each activity. The dictionary components can be used to drive scheduling, cost estimating, managing, and controlling work ^[1]. Figure 6 provides a description of each component in the WBS dictionary and an example based on figure 3.

• Some of the methods recommended by the PMI for cost estimate include expert judgement, analogous estimating, parametric estimating, and three-point estimating. However, those topics will not be covered in this article.

Steps for building an effective WBS

Evaluating the quality of a WBS

Quality Principle 1

WBS Quality Sub-Principle 1: Core Characteristics

WBS Quality Sub-Principle 2: Use-related Characteristics

Limitations

References

1. ↑ ^{1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 1.33 1.34} Project Management Institute, Inc. (PMI)., "Practice Standard for Work Breakdown Structures (3rd Ed.)", 2019
2. ↑ ^{2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10} Kerzner, H. ., "Project Management: A Systems Approach to Planning, Scheduling, and Controlling. (7th Ed.) ", 2009
3. ↑ ^{3.0 3.1} Norman, E; Brotherton, S; Fried, R. "Work Breakdown Structures: The Foundation for Project Management Excellence. ", 2008
4. ↑ Cicala, G. "The Project Managers Guide to Microsoft Project 2019: Covers Standard, Professional, Server, Project Web App, and Office 365 Version", 2019
5. ↑ ^{5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27} Bucktik, L."Secrets to Mastering the WBS in Real-World Projects: The Most Practical Approach to Work Breakdown Structures (WBS)! (2nd Ed.) PMI ", 2010