Organizational Breakdown Structure (OBS)
PMBOK v8 Definition
The Organizational Breakdown Structure (OBS) is a hierarchical representation of the project organization that illustrates the relationship between project activities and the organizational units that will perform those activities. While the WBS shows a breakdown of project deliverables, an OBS is arranged according to an organization's existing departments, units, or teams, with the project activities or work packages listed under each department. An operational department, such as information technology or purchasing, can see all of its project responsibilities by looking at its portion of the OBS.
Why It Matters for the Exam
The OBS appears frequently in PMI exam questions testing your understanding of organizational alignment and responsibility assignment. Questions typically ask you to distinguish the OBS from the WBS (deliverable-focused) and the RBS (resource-focused), or to identify which tool shows "who does what" from an organizational perspective. Expect scenario-based questions where a department needs to see its project workload.
Key Points to Remember (for the exam)
- Primary Purpose: Shows relationship between project activities and organizational units that perform them
- Structure Basis: Arranged according to organization's existing departments, units, or teams
- Key Distinction from WBS: WBS = breakdown of project deliverables; OBS = breakdown by organizational responsibility
- Practical Use: Each department sees all its project responsibilities by examining its OBS portion
- Common Department Examples: Information technology, purchasing, engineering, testing
- Relationship to WBS Dictionary: The WBS dictionary includes "responsible organization" as a standard field
- Complementary Tool: Used alongside WBS and Resource Breakdown Structure for complete project decomposition
Typical PMI Exam Example
A project manager is creating documentation to help the IT department understand all of its responsibilities across the project. The project manager needs a tool that organizes work by department rather than by deliverable. Which structure should the project manager use?
Answer: Organizational Breakdown Structure (OBS)
PMI Exam Traps
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Trap: Confusing OBS with WBS Reality: WBS organizes by deliverables; OBS organizes by organizational units/departments
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Trap: Thinking OBS shows individual roles Reality: OBS shows departments/units/teams, not individual names (RAM/RACI does individual assignments)
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Trap: Assuming OBS is a resource planning tool Reality: OBS is a responsibility alignment tool; Resource Breakdown Structure (RBS) handles resource categories
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Trap: Believing OBS replaces the WBS dictionary Reality: The WBS dictionary includes "responsible organization" as a field, but OBS provides a separate hierarchical view
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Work Breakdown Structure (WBS) | Complementary opposite | WBS = deliverables; OBS = organizational units performing work |
| Resource Breakdown Structure (RBS) | Complementary tool | RBS = resource categories; OBS = organizational departments |
| WBS Dictionary | Supporting document | WBS dictionary includes "responsible organization" field linked to OBS |
| Responsibility Assignment Matrix (RAM) | Implementation tool | RAM assigns specific roles; OBS shows department-level responsibility |
Quick Review Questions
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A purchasing department manager wants to see all project activities assigned to their team. Which structure provides this view?
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What is the fundamental difference between how a WBS and an OBS are arranged?
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In the WBS dictionary, which field directly supports the OBS concept?
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An OBS is arranged according to what existing organizational structure?
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Which two other breakdown structures are commonly used alongside the OBS for complete project decomposition?
PMBOK v8 Reference
Section 5 – Tools and Techniques, pages 171-172