Chapter 2
Defining the WBS
2.1 Overview
A project is made more manageable by breaking it down into individual components that together are known as a Work Breakdown Structure or WBS. Such a structure defines unique work elements that can be arranged and completed in the order defined by the network diagram: sequentially, in parallel, or in the specific order necessary to accomplish project outcomes. It facilitates other project management processes such as estimating, scheduling, resource allocation, risk analysis, and measurement and control of the project. The WBS represents a clear description of the project's deliverables and scope—the “what” of the project. It is not a description of a process or schedule that defines how or when the deliverables will be produced, but rather is specifically limited to describing and detailing the project's outcome or scope. As stated in the PMBOK® Guide—Third Edition, “The WBS organizes and defines the total scope of the project. The WBS subdivides the project work into smaller, more manageable pieces of work, with each descending level of the WBS representing an increasingly detailed definition of the project work. The planned work contained in the lowest level WBS components, which are called work packages, can be scheduled, cost estimated, monitored, and controlled.”
This chapter will provide more information regarding WBS terms, concepts, the 100% Rule, and an example of a good WBS in action. The remaining sections of this chapter include:
2.5 WBS for Construction of a Bicycle
2.6 Representations of the WBS
2.2 Common Usage of Terms
A WBS, as defined in the PMBOK® Guide—Third Edition, is: “A deliverable-oriented hierarchical decomposition of the work to be executed by the project team to accomplish the project objectives and create the required deliverables. It organizes and defines the total scope of the project. Each descending level represents an increasingly detailed definition of the project work.…” The following terms help clarify this dictionary definition:
Work. Sustained physical or mental effort, exertion, or exercise of skill to overcome obstacles and achieve an objective. Commonly used to refer to a specific activity, duty, function, or assignment often being a part or phase of some larger undertaking; something produced or accomplished by effort, exertion, or exercise of skill. In this context, work refers to work products or deliverables that are the result of effort and not to the effort itself.
Breakdown. Division into parts or categories; separation into simpler substances; decomposition.
Structure. Something arranged in a definite pattern of organization.
These dictionary definitions imply that a WBS has the following characteristics:
- Supports the definition of all work required to achieve an objective, tangible result.
- Is constructed to illustrate and define the hierarchy of deliverables. This hierarchy is organized into “parent-child” relationships.
- Has an objective or tangible result that is referred to as a deliverable. In a sense, the WBS can be thought of as a “deliverable” breakdown structure.
Additionally, as noted above, the WBS is a deliverable-oriented hierarchical decomposition of the work to be executed by the project team. It can thus be defined in the following terms:
Deliverable. Any unique and verifiable product, result, or capability to perform a service that must be produced to complete a process, phase, or project. Often used more narrowly in reference to an external deliverable, which is a deliverable that is subject to approval by the project sponsor or customer.
Oriented. Aligned or positioned with respect to a point or frame of reference; focused toward the concerns and interests of a specific group.
Hierarchical. Classified according to various criteria into successive levels or layers.
Decomposition. A planning technique that subdivides the project scope and project deliverables into smaller, more manageable components, until the project work associated with accomplishing the project scope and providing the deliverables is defined in sufficient detail to support executing, monitoring, and controlling the work.
These definitions work together to define the overall role of the WBS, that is, to provide a foundation for the development of project schedules, communications, risk management plans, as well as other key project elements.
2.2.1 Definition of Terms
The following definitions represent WBS-related terms as defined by the PMBOK® Guide—Third Edition. These terms and others listed in the Glossary of this standard facilitate understanding of the integral role the WBS plays in project management practice. Terms are listed here in alphabetical order.
Activity. A component of work performed during the course of a project.
Apportioned Effort. Effort applied to project work that is not readily divisible into discrete efforts for that work, but which is related in direct proportion to measurable discrete work efforts. Contrast with discrete effort.
Control Account. A management control point where scope, budget (resource plans), actual cost, and schedule are integrated and compared to earned value for performance measurement. Control accounts are placed at selected management points (specific components at selected levels) of the work breakdown structure. Each control account may include one or more work packages, but each work package may be associated with only one control account. Each control account is associated with a specific single organizational component in the organizational breakdown structure (OBS). Previously called a cost account. See also work package.
Discrete Effort. Work effort that is separate, distinct, and related to the completion of specific work breakdown structure components and deliverables, and that can be directly planned and measured. Contrast with apportioned effort.
Level of Effort (LOE). Support-type activity (e.g., seller or customer liaison, project cost accounting, project management, etc.), which does not produce definitive end products. It is generally characterized by a uniform rate of work performance over a period of time determined by the activities supported.
Task. A term for work whose meaning and placement within a structured plan for project work varies by the application area, industry, and brand of project management software.
Work Breakdown Structure Component. An entry in the work breakdown structure that can be at any level.
Work Package. A deliverable or project work component at the lowest level of each branch of the work breakdown structure. The work package includes the schedule activities and schedule milestones required to complete the work package deliverable or project work component. See also control account.
The following definition is included to reflect common usage:
WBS Element. Any single work breakdown structure (WBS) component and its associated WBS attributes contained within an individual work breakdown structure.
2.3 Concept
2.3.1 Overview
The WBS assists project leaders, participants, and stakeholders in the development of a clear vision of the end products or outcomes produced by the project. To be more precise, the WBS provides a clear vision of the work of the project. The WBS divides the project scope into hierarchical, manageable, definable packages of work that balance the control needs of management with an appropriate and effective level of detailed project data. The WBS provides the framework for all deliverables across the project life cycle. The various levels of the WBS also provide support for focusing communication with stakeholders and aid in clearly identifying accountability to a level of detail necessary for effectively managing and controlling the project.
The upper levels of the WBS typically reflect the major deliverable work areas of the project or major phases in the project's life cycle. These levels also provide logical summary points for assessing team and individual performance, communicating accomplishments, and measuring cost and schedule performance with respect to individual deliverables as well as the overall project.
The content of the upper levels can vary, depending upon the type of project and the industry involved. To avoid confusion and rework, it is often prudent to define the levels of the WBS prior to its construction. The lower WBS elements provide appropriate focus for project management processes such as scope and schedule development, cost estimating and resource allocation, and risk assessment.
Whenever work is logically structured, easily identifiable, and clearly within the capabilities of individuals, project stakeholders can confidently expect that objectives associated with the work can and will be achieved. The use of a WBS helps ensure that the project meets these criteria.
2.3.2 Deliverables
The underlying concept of a deliverable is the core of a WBS. The PMBOK® Guide—Third Edition defines a deliverable as:
Any unique and verifiable product, result, or capability to perform a service that must be produced to complete a process, phase, or project. Often used more narrowly in reference to an external deliverable, which is a deliverable that is subject to approval by the project sponsor or customer.
The WBS provides the foundation for integrating the work package and intermediate deliverables with all other aspects of project initiation, planning, execution, monitoring and controlling, and closing.
A deliverable-oriented WBS provides many benefits to the project, including the following:
- Better communication to project sponsors, stakeholders, and team members
- More accurate estimation of tasks, risks, timelines, and costs
- Increased confidence that 100% of the work is identified and included
- A foundation for the control processes within the project.
The deliverable concept and deliverable orientation of the WBS are integral to understanding the proper definition and use of the WBS and the benefits it provides within the larger context of all project management processes.
2.3.3 Design
A well-designed WBS that presents information at the appropriate level of detail and in formats and structures meaningful to those performing the work is an invaluable tool in project management. It provides a graphical representation or textual outline of the project scope. Here are some roles the WBS plays in supporting clarity for project definition:
- Decomposes (or disassembles) the overall project scope into deliverables and supports the definition of the work effort required for effective management
- Clearly and comprehensively defines the scope of the project in terms of deliverables that the project participants and stakeholders can understand
- Supports documentation of the accountability and responsibility for the various deliverables by having a direct relationship among the WBS elements related to the Organizational Breakdown Structure (OBS) identified through the Responsibility Assignment Matrix (RAM)
- Provides a structure for organizing information regarding the project's progress, periodic status, and projected performance for which a project manager is responsible
- Supports tracking of risks to assist the project manager in identifying and implementing responses necessary to achieve desired outcomes.
2.3.4 Management
The WBS supports effective project management in several ways during the life of a project by:
- Separating project deliverables into component parts to ensure the project plan matches the approved project scope and will fulfill the overall objectives of the project
- Supporting the decomposition of project scope into simpler components, providing one of the primary methods for managing complex projects
- Providing a framework for specifying performance objectives
- Providing the basis for integrating and assessing schedule and cost performance
- Supporting the planning and assignment of responsibilities
- Assisting in determining resource requirements such as technical skills, experience and knowledge
- Facilitating the reporting and analysis of project progress and status data, including resource allocations, cost estimates, expenditures, and performance.
2.3.5 Organizational Perspective
The WBS provides the foundation for assigning work to the appropriate organizational units, subcontractors, or individuals. As the work and organizational responsibilities become more clearly defined, individuals, including subcontractors, are assigned responsibility for accomplishing specific WBS elements within defined budgets and schedules.
2.3.6 WBS Levels
The WBS includes all work to be done by the project leaders, stakeholders, and both internal and external participants, such as team members and subcontractors. The WBS provides a clear statement of the objectives and deliverables of the work to be performed. The depth of a WBS is dependent upon the size and complexity of the project and the level of detail needed to plan and manage it. Most work breakdown structures consist of a multi-level hierarchy describing the entire scope to be accomplished by the performing organization; however, the specific number of levels should be appropriate for effectively managing the project in question.
2.4 The 100% Rule
The 100% rule (Haugan, 2002, p 17) is a core characteristic of the WBS. This rule states that the WBS includes 100% of the work defined by the project scope and captures ALL deliverables—internal, external, and interim—in terms of work to be completed, including project management. The 100% rule is one of the most important principles guiding the development, decomposition and evaluation of the WBS. The rule applies at all levels within the hierarchy: the sum of the work at the “child” level must equal 100% of the work represented by the “parent” and the WBS should not include any work that falls outside the actual scope of the project, that is, it cannot include more than 100% of the work.
It is important to remember that the 100% rule also applies at the activity level. The work represented by the activities in each work package must add up to 100% of the work necessary to complete the work package.
2.5 WBS for Construction of a Bicycle
The scope of a project can be decomposed in multiple ways. Regardless of the manner of decomposition, the sum of the work packages for each different decomposition should add up to the same scope of work. The following sample WBS illustrates key concepts that will be discussed throughout the remaining chapters of this standard.
Figure 2-1 is a sample WBS designed to capture the scope of work required to construct a custom bicycle. To keep the graphic simple, this particular WBS does not differentiate among the many types of bicycles that can be built from similar WBS constructs, for example, a road bicycle, mountain bicycle, racing bicycle, or any other bicycle, but assumes that detailed requirements for a specific type of bicycle would be provided as further decompositions of the illustrated WBS elements.
This particular example was selected for its simplicity to enable the reader to focus on the WBS itself, rather than the multitude of alternatives, options, and components required to define a complex, unique, and perhaps esoteric product. The bicycle is a familiar and common product, an example that easily suggests the processes required to produce the end result.
This illustration shows how concepts and guidance described in later chapters work together to produce a completed bicycle that meets the quality, timeliness, features, and functionality requirements of the project sponsor, which in this case is the purchaser.
Specifically, this WBS illustrates the various levels of a WBS, the numbering scheme, naming convention, relationship of parent and child WBS elements, and the representation of each of these characteristics and principles working together to form a complete WBS. This illustration represents one example of the possible decomposition of the testing elements. It is not intended to be comprehensive or definitive.
The bicycle WBS helps to communicate and reinforce some of the concepts presented. The annotated illustration (Figure 2-2) immediately following shows that all WBS elements are not decomposed to the same extent. For example, this hypothetical bicycle WBS does not decompose each Level 2 WBS component further into subelements. While it can be helpful to decompose the entire WBS to the same level for some projects, there are no hard and fast rules dictating that each WBS element is decomposed to the same level. Decomposition is a use-related characteristic that is defined by the context of the project the WBS is developed to support. This concept is presented in detail in Chapter 4, Section 4.2.
Additionally, this example communicates WBS concepts that reflect application in a broad array of industries. The construction of the WBS can remain the same, such as the relationship of the WBS elements, the decomposition level, and the relationship to other WBS elements. The content can be modified to reflect the application of the concept in alternate terms for other industries, projects, or programs. This is illustrated in the decomposed elements that are identified below the Level 2 WBS element for Integration (1.6). In Figure 2-2, elements 1.6.4.1–1.6.4.3 are called Component Test, Product Test and Customer Test, respectively. In the next example, Figure 2-3, these same elements are entitled Unit Test, System Test, and Acceptance Test, showing how the concept of testing is represented in various ways using basic WBS elements.
Finally, throughout the standard, the bicycle WBS is repeatedly used as a reference point to clarify and illustrate concepts. To illuminate the concept being discussed, parts of the WBS are extracted, elements are singled out, or sets of decomposed elements are highlighted by placing dotted lines around them. For clarity, these WBS elements are frequently shown in a number of different representations.
2.6 Representations of the WBS
The WBS can be represented in a variety of ways including graphical, textual, or tabular views. Regardless of the representation used, the WBS enables the project team to predict and forecast costs, schedules, resource requirements, and allocations more accurately. Two common methods are the hierarchy diagram and the outline or tabular view as shown in Figure 2-4.
2.7 Summary
In summary, the WBS:
- Defines the hierarchy of deliverables
- Supports the definition of all work required to achieve an end objective or deliverable(s)
- Provides a graphical representation or textual outline of the project scope
- Provides the framework for all deliverables across the project life cycle
- Provides a vehicle for integrating and assessing schedule and cost performance
- Facilitates assignment of resources
- Facilitates the reporting and analysis of progress and status data
- Provides a framework for specifying performance objectives.