Chapter 3

Importance of the WBS

3.1 Overview

A WBS can not alone ensure project success, but consider that the WBS does the following:

• Defines all the work of the project, and only the work of the project, thereby clarifying the project scope
• Reflects the input from all team members to ensure buy-in
• Provides the baseline for subsequent change control
• Is a primary input to other project management processes—for example, resource planning, cost estimating, schedule development, and risk identification
• Provides the framework for project control, performance monitoring, and the foundation for communication with all stakeholders
• Ensures the work of the project correlates appropriately with the Responsibility Assignment Matrix (RAM) and the Organizational Breakdown Structure (OBS)
• Is referenced in other PMI standards, for example, the PMBOK® Guide—Third Edition and Practice Standard for Earned Value Management (EVM), as an essential planning deliverable supporting key project management functions.

Experienced project managers know that there are many things that can go wrong in projects regardless of how successful the project managers are in the planning and execution of their work. Project failures, however, can often be traced back to a poorly developed or nonexistent WBS.

A poorly constructed WBS can result, among other things, in the following project stumbling blocks and adverse project outcomes:

• Incomplete project definition leading to ongoing project extensions
• Unclear work assignments, goals, objectives, or deliverables
• Scope creep or unmanageable, frequently changing scope
• Budget overrun
• Missed deadlines on scheduled deliverables, or timeline slippage
• Unusable new product or feature
• Failure to deliver on some elements of project scope.

The remainder of this chapter highlights in more detail the important role the WBS plays in project and program management planning:

3.2 Integration with Project Management Processes

3.3 Relationship to Other Tools

3.4 WBS Integration and Use by Other Standards

3.5 Summary

3.2 Integration with Project Management Processes

The WBS is created in the Create WBS Planning Process (PMBOK® Guide—Third Edition). The WBS also plays an integral role in other project management processes. Typical (though not exhaustive) examples are shown in Table 3-1. References in Table 3-1 are to sections in the PMBOK® Guide—Third Edition.

Table 3-1. Project Management Processes

3.3 Relationship to Other Tools

3.3.1 Project Management Tools

The purpose of the WBS, as a project management tool, is to organize the scope of a project. WBS definition for programs and portfolios can use similar techniques to organize scope. There are many project management tools that use the WBS or its components as input (see Section 5.3 of PMBOK® Guide—Third Edition).

.1 Project Charter.

The WBS takes the project charter as its starting point. The highest level element in the WBS should represent the project's overall end-point product(s), service(s), or outcomes as described in the project charter. If the project's major products cannot be described during the creation of the WBS, then the project management team should examine the charter to determine if it has been sufficiently defined.

.2 Project Scope Statement.

The scope statement for the project is intended to clearly and succinctly describe what the project is and is not intended to accomplish. The high-level elements in the WBS should match, word-for-word, the nouns used to describe the outcomes of the project in the scope statement. If the project management team has difficulty identifying the objects in the scope statement and applying them to the high-level WBS elements, the team should carefully examine the scope statement to determine if it sufficiently captures all project outcomes and deliverables. The WBS Dictionary can also be used to further document and clarify each deliverable (see 3.3.1.6).

.3 Program and Portfolio WBS.

The WBS can be used to define scope for projects, programs, and portfolios. For example, program offices are typically established to share tools, techniques, methodologies, and resources in managing one or more collections of related projects as program(s). The project WBS must illustrate a clear understanding of the relationship among highly decomposed work packages within individual projects and program (or higher order) scope definitions. If strategic changes are made, the impact on projects, resources, and budgets can be easily calculated, assuming the project WBS has been constructed correctly in consideration of these higher order factors.

.4 RBS.

The Resource Breakdown Structure (RBS) describes the project's resource organization and can be used in conjunction with the WBS to define work package assignments. The link between work packages and the RBS can be used to verify that all members of the project team have been appropriately assigned work packages, and that all work packages have owners.

.5 OBS.

The Organizational Breakdown Structure (OBS) is loosely related to the WBS. The OBS depicts the organization hierarchy, allowing the project's work packages to be related to the performing organizational units. This tool reinforces the guideline that each work package should have a single point of responsibility. The OBS can be a useful tool for project managers in that it clearly demonstrates the hierarchy of people or groups, whereas the WBS is strictly organized by deliverables.

.6 WBS Dictionary:

The WBS dictionary is a key document that accompanies the WBS and carries critical project information. The WBS dictionary defines, details, and clarifies the various elements of the WBS to ensure that each component of the WBS is accurately articulated and can be communicated to anyone referencing the WBS. The development of the WBS dictionary often uncovers ambiguity or other errors in the WBS itself, and results in revisions to the WBS. The WBS dictionary contains information about each element of the WBS, including a detailed description of the work, deliverables, activities, and milestones associated with each element. The WBS dictionary might also include an indication of the type and number of resources required and contract control information, such as a charge number or other similar data. Often, a WBS dictionary will include traceability matrices linking the WBS to other scope control documents such as statements of work or requirements documents.

.7 Project Schedule Network Diagram:

The network diagram is a sequential arrangement of the work defined by the WBS, and is essential to uncovering project dependencies and risks. The activities within the WBS work packages are arranged to show precedence and order. Developing the network diagram often uncovers problems in the WBS, such as incomplete decomposition, the assignment of too much work in an element, or the assignment of more than one person for an individual WBS element, thus resulting in needed revisions.

.8 Project Schedule:

The various elements of the WBS are used as starting points for defining the activities included in the project schedule. Implied dependencies can be recorded in the WBS Dictionary, and the activities as described in the WBS Dictionary are then included as detail in the schedule.

3.3.2 Interrelationships Among Project Management Tools

Because of interrelationships among the WBS and other project management tools, it is important to note that any change in the WBS requires an associated change in the related tools.

Such interrelationships among the WBS and other Project Management processes are described throughout the PMBOK® Guide—Third Edition. As an example of these interdependencies, consider the relationship between the WBS and the activity list used for the project schedule as described in Section 6.1.2 of the PMBOK® Guide—Third Edition (Activity Definition: Tools and Techniques). Specifically, item 6.1.2.1 (Decomposition) reads:

“The technique of decomposition, as it is applied to activity definition, involves subdividing the project work packages into smaller, more manageable components called schedule activities. The Activity Definition process defines the final outputs as schedule activities rather than as deliverables, as is done in the Create WBS process (Section 5.3).”

“The activity list, WBS, and WBS dictionary can be developed either sequentially or concurrently, with the WBS and WBS dictionary being the basis for development of the final activity list. Each work package within the WBS is decomposed into the schedule activities required to produce the work package deliverables. This activity definition is often performed by the project team members responsible for the work package.”

Section 6.2 of the PMBOK® Guide (Activity Sequencing) further states:

“Activity sequencing involves identifying and documenting the logical precedence relationships among schedule activities. Schedule activities can be logically sequenced with proper precedence relationships, as well as leads and lags to support later development of a realistic and achievable schedule.”

This discussion briefly describes how many project management tools are interrelated, all based upon the foundation of the WBS. The Work Breakdown Structure plays a pivotal role in project and program management in each of the process groups: Initiating, Planning, Executing, Monitoring & Controlling and Closing for which it ensures a consistent definition of the scope of the work to be undertaken.

3.3.3 WBS Development Tools

There are a number of project management tools that can be used to assist a project manager with the development of a WBS. These tools include outlines and organization charts, fishbone and brainstorming techniques, and top down and bottom up development strategies. There are many WBS templates available, and corporate standards can be referenced or copied for quick-starting WBS development. When using generic or corporate WBS templates, it will be important to ensure that the template chosen for the project closely matches the project type (such as a Construction WBS template, an IT Software Development WBS template, a commercial product WBS template, etc.) and is used as a guide or basic structure that is then customized to fit the needs of the specific project being planned. (More information about these tools can be found in Chapter 5 of this standard.)

There are many benefits to using tools to develop a WBS. For example, tools often promote consistency and repeatability in the development of a WBS, especially enterprise productivity tools. WBS tools can also promote and enforce the principles of the WBS standard and can significantly reduce the development effort, simplifying the WBS process, and even promoting reusable WBS products.

3.4 WBS Integration and Use by Other Standards

Scope management is integral to other PMI standards. These include but are not limited to: the PMBOK® Guide—Third Edition; Practice Standard for Earned Value Management (EVM), and Organizational Project Management Maturity Model (OPM3®). The development of a quality WBS is critical to the successful execution of project management processes, as described in the PMBOK® Guide—Third Edition, as well as in the other aforementioned standards.

Standards that take advantage of the WBS typically fall into one of two categories. The first category focuses on using the content output of the WBS as an input. PMI's Practice Standard for Earned Value Management (EVM) and upcoming Practice Standard for Scheduling fall into this category. Since the content output from a WBS is predictable and well understood, such standards can build upon or leverage the Practice Standard for Work Breakdown Structures—Second Edition.

Other standards incorporate the WBS (as defined by this practice standard) as the preferred tool to develop the scope definition for their role. For example, the PMBOK® Guide—Third Edition uses the Practice Standard for Work Breakdown Structures— Second Edition to develop the project scope, and OPM3® identifies the WBS as a tool that can be used to develop a program WBS. These standards recognize the Practice Standard for Work Breakdown Structures—Second Edition as representing good practice.

The WBS is developed to define carefully what is in the project scope and, by implication, what is out of scope. The Practice Standard for Scheduling (currently in development) is based, in part, on an assumption that a high-quality WBS has been developed using good practice, correctly defining project scope. When the project schedule is developed, each high-level (summary) task must correspond to a WBS element. If an activity or task does not have a relationship to a work package within the WBS, then either the WBS does not fully encompass the project scope, or the activity or task is unnecessary.

EVM is a management methodology for integrating scope, schedule, and resources, and for objectively measuring project performance and progress. The data used in EVM are dependent upon WBS elements having been developed using good practice. If WBS elements are not well defined, are too large in scope, are too lengthy in duration, or are in some other manner not appropriately decomposed or developed, it will be difficult to measure the project's earned value. The Practice Standard for Earned Value Management relies upon a high-quality WBS as a key input.

The PMBOK® Guide—Third Edition, PMI's project management standard, discusses project management practice as a whole. A core element of project management is scope management, and the PMBOK® Guide discusses the benefits of using the WBS as a technique to manage and control a project's scope.

The Standard for Program Management describes how collections of related projects are best managed. This standard assumes that the WBS for each relevant project is developed according to good practice and accurately describes the scope for the project.

The Standard for Portfolio Management describes how collections of projects or programs are best managed. This standard assumes that the WBS for each relevant project/program is developed according to good practice and accurately describes the scope for the project.

PMI's OPM3® is an example of a maturity model that can be used to measure and detail an organization's maturity level, as well as provide a clear path to higher levels of maturity. The WBS is important to OPM3®, since OPM3® relies on the benefits of processes aimed at scope management. This standard relies on the development of a quality WBS as a foundation for effective project management.

3.5 Summary

The WBS is an important tool used in the planning and execution of a successful project. Many project cost, schedule, and quality failures can be traced directly to flaws in the development of the project's WBS. It is less likely that a project will be successful without the existence of a quality WBS. In contrast, developing and applying a high quality WBS will significantly increase the likelihood of successful project completion. Chapter 4 will provide insight into the characteristics and components that make up a high-quality WBS.