Work Breakdown Structure: Work Components and Decomposition

PMBOK v8 Definition

The Work Breakdown Structure (WBS) is a hierarchical decomposition of the total scope of work to be carried out by the project team to accomplish the project objectives and create the required deliverables. The WBS represents all product and project work, including the project management work, organized into work packages—the lowest level of the WBS for which cost and duration can be estimated and managed.

Why It Matters for the Exam

WBS concepts appear frequently in PMI exam questions related to Scope Management, particularly in questions testing your understanding of decomposition, the 100% rule, and rolling wave planning. You will encounter these in situational questions asking you to identify the correct level of decomposition or the proper approach for organizing work components.

Key Points to Remember (for the exam)

• 100% Rule: The total of the work at the lowest levels should roll up to the higher levels so that nothing is left out and no extra work is performed
• Work Package Definition: The work defined at the lowest level of the WBS for which cost and duration can be estimated and managed
• Decomposition Approaches: Top-down approach, organization-specific guidelines, WBS templates, and bottom-up approach for grouping subcomponents
• Rolling Wave Planning: Decomposition may not be possible for deliverables far into the future; the team waits until the deliverable is agreed upon to develop WBS details
• Excessive Decomposition Risk: Leads to nonproductive management effort, inefficient resource use, decreased performance efficiency, and difficulty aggregating data
• WBS Structure Forms: Can be organized by project life cycle phases (second level), major deliverables (second level), or incorporating subcomponents from organizations outside the project team
• Contract WBS: When work involves organizations outside the project team (contracted work), the seller develops the supporting contract WBS

Typical PMI Exam Example

A project manager is creating the WBS for a construction project. The project includes both internal work and work to be performed by an external contractor. The project manager decomposes internal deliverables to the work package level. For the contracted portion, what should the project manager do?

Correct approach: The seller (contractor) develops the supporting contract WBS as part of the contracted work, while the project manager ensures the WBS incorporates these subcomponents at the appropriate level.

PMI Exam Traps

• Trap: Confusing work packages with activities

• Reality: Work packages are WBS components at the lowest level; activities are derived from work packages during schedule development

• Trap: Thinking decomposition must be done completely upfront for all deliverables

• Reality: Rolling wave planning allows waiting until deliverables are agreed upon for detailed decomposition

• Trap: Believing more decomposition always improves control

• Reality: Excessive decomposition creates nonproductive management effort, inefficient resource use, and decreased performance efficiency

• Trap: Assuming the WBS only includes product deliverables

• Reality: The WBS represents ALL product AND project work, including project management work

Important PMI Connections

Quick Review Questions

1. What is the 100% rule in WBS decomposition and why is it critical for scope management?

2. A project has work packages that are too detailed, causing difficulty in aggregating data. What principle has been violated?

3. When should a project manager use rolling wave planning instead of full decomposition?

4. Who develops the contract WBS when work involves organizations outside the project team?

5. What are the three popular approaches for creating a WBS structure?

PMBOK v8 Reference

Section 5.3 - Create WBS (Scope Management Knowledge Area, Planning Process Group)