6.2 WBS, Work Packages, and Activity Definition

Decomposition and the WBS

The Work Breakdown Structure (WBS) is a deliverable-oriented hierarchical decomposition of the total scope of work the project team must execute. It is built through decomposition — subdividing project deliverables into smaller, more manageable components. A critical exam distinction: the WBS organizes deliverables (nouns), not activities (verbs). Activities come later, during schedule planning.

Steps to create a WBS

1. Identify the major deliverables and the project-management work
2. Organize the deliverables into a logical hierarchy
3. Decompose upper-level deliverables into lower-level components
4. Assign identification codes (the WBS numbering scheme, e.g., 1.2.3)
5. Verify the result against the 100% Rule

Decomposition guidelines

The WBS Dictionary

The WBS dictionary is the companion document that gives detailed information about each WBS element so the work is unambiguous to whoever performs it.

The scope baseline is a key exam term: it equals the approved scope statement + WBS + WBS dictionary together. A change to any of the three is a change to the scope baseline and must go through change control.

From Work Packages to Activities

WBS -> Work Packages -> Activities -> Schedule

Define Activities decomposes each work package into the activities required to produce it. Each activity carries activity attributes: ID and name, predecessors and successors, logical relationships, leads and lags, resource requirements, and any imposed dates (date constraints).

Rolling Wave Planning

Rolling wave planning is a form of progressive elaboration: near-term work is planned in detail at the activity level, while work further out is held at a higher level — a planning package (a known work component below a control account but above work packages) or simply a coarse work package. As the project advances, those future components are elaborated into detailed activities.

Use it when:

• The full scope cannot be defined in detail at the outset
• Requirements for later phases depend on the results of earlier phases
• The project is long and future conditions are uncertain

Key distinction (commonly tested): Rolling wave planning is NOT scope creep. The total scope is still captured (at a high level) in the WBS and stays controlled; only the level of detail increases over time. Scope creep, by contrast, is uncontrolled expansion of scope without change-control approval.

Milestones and the Milestone List

A milestone is a significant point or event in a project with zero duration — it consumes no time or resources itself; it marks the completion of a deliverable, phase, or other key event.

Milestones drive schedule planning and progress tracking, stakeholder reporting, phase-gate reviews, and — in fixed-price work — contract payment triggers.

Worked example of the 100% Rule: A WBS element "3.0 Website" decomposes into 3.1 Front-end, 3.2 Back-end, and 3.3 Content. If 3.1 + 3.2 + 3.3 do not together cover everything the website requires (say, hosting setup was forgotten), the WBS violates the 100% Rule. The fix is to add the missing deliverable, not to inflate an existing branch.

Control Accounts and the Code of Accounts

Above the work-package level, related work packages may roll up into a control account — a management control point where scope, budget, and schedule are integrated and compared to earned value for performance measurement. Each control account can contain one or more work packages, and each work package belongs to exactly one control account. The code of accounts is the numbering system (1, 1.1, 1.1.2, and so on) that uniquely identifies every WBS component and lets costs and schedule roll up cleanly.

Why the WBS Matters Downstream

The WBS is not busywork; it is the foundation other planning processes depend on. Cost and duration estimates are built at the work-package level and aggregated upward. Risk identification uses the WBS to ensure no branch of scope is overlooked. The schedule is built from activities decomposed out of work packages. And scope verification ("Validate Scope") compares completed deliverables against WBS-defined acceptance criteria.

Common trap: Questions that list verbs ("write code," "test module") as WBS elements are testing whether you know the WBS holds deliverables, not activities. Activities belong in the activity list produced by the Define Activities process, one level below the work package.