PMGT1860 · Project Initiation and Scope
Work & Organisational Breakdown Structures
Week 6 teaches the Work Breakdown Structure — the tool that organises and defines the total scope and becomes the basis for planning, budgeting and resourcing — decomposed down to work packages, plus the Organisational Breakdown Structure that assigns responsibility. Building a correct WBS (obeying the 100% rule) is a required part of the group initiation plan, and the WBS rules and the work-package definition are frequently quizzed.
What this chapter covers
- 01In-scope vs out-of-scope activities as the project boundary
- 02WBS defined (PMBOK) — a hierarchical decomposition of the total scope of work into deliverables
- 03Role of the WBS — visualises scope, verifies completeness, is the scope baseline for change control; describes the 'what' (deliverables), NOT the schedule/timing or reporting lines
- 04Decomposition and the work package — the lowest level at which cost, effort, duration and resources can be estimated
- 05The four WBS levels — Top Level → Control Account → Work Packages → Activities
- 06Representations — indented outline, tree/org-chart, Gantt; organising schemes — deliverable-based vs phase-based
- 07The 100% rule and WBS rules — children sum to 100% of the parent, no duplication, nouns not verbs, coding scheme, include PM work
- 08Organisational Breakdown Structure (OBS) and the link to the Responsibility Assignment Matrix (RAM)
Applied: decompose to work packages and apply the 100% rule
- +1(a) Top level (1.0) = Music Festival. Control accounts: 1.1 Venue & Site, 1.2 Programme & Talent, 1.3 Marketing & Ticketing. Use nouns/adjectives, not verbs, because the WBS describes deliverables, not actions.
- +1Add one work package under each: 1.1.1 Site layout plan; 1.2.1 Artist line-up contracts; 1.3.1 Ticketing platform setup. The coding (1.0, 1.1, 1.1.1) makes the hierarchy explicit.
- +1(b) The 100% rule requires that the WBS captures 100% of the scope, and at every level the child items sum to exactly 100% of their parent — no more, no less — including project-management work itself.
- +1A violation to avoid: a '1-within-1' (a category containing only one child), an activity placed under two parents (not mutually exclusive), or sequencing tasks by time — chronology belongs to the schedule, not the WBS.
- +1(c) A work package is the lowest level of the WBS at which cost, effort and duration can be estimated and the work managed and assigned — it is not the top-level deliverable and not the schedule.
Key terms
- Work Breakdown Structure (WBS)
- A hierarchical decomposition of the total scope of work to be carried out to accomplish the objectives and create the required deliverables. It describes the 'what' (deliverables), not the schedule or reporting lines, and provides a scope baseline for change control.
- Decomposition
- Dividing and subdividing project scope and deliverables into smaller, more manageable parts, down to a level where cost and duration can be estimated.
- Work package
- The work defined at the lowest level of the WBS, for which cost, effort, duration and resources can be estimated and managed — the point where activities are defined, the timeline forms and resources are assigned.
- The 100% rule
- The WBS includes 100% of the work defined by the scope — all deliverables, including project-management work — and at every level the sum of the child items equals exactly 100% of the parent, with no exception.
- WBS organising schemes
- The two main ways to organise a WBS: deliverable-based (grouped by outputs/products/documents) and phase-based (grouped by life-cycle stages). Less common: verb-oriented, noun/product-oriented, and time-phased.
- Organisational Breakdown Structure (OBS)
- A hierarchical representation of the project organisation that maps organisational units to the work they perform; combining WBS work packages with the OBS produces the Responsibility Assignment Matrix (RAM).
Work & Organisational Breakdown Structures FAQ
What is the difference between the WBS and a schedule?
The WBS describes the 'what' — the deliverables and work, decomposed into a hierarchy — while the schedule describes the 'when'. The WBS deliberately ignores chronology and reporting lines; sequencing tasks in time is the schedule's job. A common quiz error is to describe a WBS as 'tasks in the order they happen', which is wrong.
What is the 100% rule and why does it matter?
It is the most important WBS principle: the WBS must contain 100% of the work defined by the scope, and at every level the child items must sum to exactly 100% of their parent — no missing work and no extra. It matters because it makes the WBS a complete, non-overlapping map of the project, which is why it can serve as the scope baseline for later change control. Remember it also includes project-management work itself.
What exactly is a work package?
The work package is the lowest level of the WBS — the level at which cost, effort and duration can be estimated and the work can be managed and assigned to one person or a work-package manager. It is not the top-level deliverable and not a stakeholder or risk list. You decompose down until an item is clear enough to estimate and own, then stop.
How does the WBS connect to the group presentation?
A correct WBS is expected in the group Comprehensive Project Initiation Plan — it shows you can turn a scope statement into an organised, deliverable-oriented structure that later supports estimating and responsibility assignment. Presenting a coded, deliverable-based WBS that passes the 100% rule signals a credible plan. Confirm the group brief's expectations on Canvas.
Assessment move
Build a WBS by hand this week rather than just reading the rules. Take a project you know, decompose it top level → control accounts → work packages with a coding scheme (1.0, 1.1, 1.1.1), and check it against the 100% rule and the traps (no 1-within-1s, nouns not verbs, no time-sequencing, include PM work). Be able to name the two main organising schemes (deliverable-based vs phase-based) and define a work package precisely. Note the OBS→RAM link, which sets up Week 7's RACI. Add a journal line on decomposing a task, and confirm quiz timing on Canvas.
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