6.2 WBS, Work Packages, and Activity Definition
Key Takeaways
- The WBS is created using decomposition — breaking down deliverables into smaller, more manageable components
- Work packages should be detailed enough to estimate cost and duration but not so detailed that management overhead exceeds the work itself
- Activities are derived from work packages through further decomposition and are the smallest units of work scheduled on the project timeline
- The WBS dictionary provides detailed descriptions of each WBS element including scope description, deliverables, assumptions, and constraints
- The rolling wave planning approach plans near-term work in detail while leaving future work at a higher level to be elaborated later
The Work Breakdown Structure and its decomposition into activities form the backbone of predictive project planning. This section covers Domain 2, Task 2 concepts related to defining and organizing project work.
Decomposition Process
Decomposition is the technique of subdividing project deliverables and project work into smaller, more manageable components.
Steps to Create a WBS
- Identify major deliverables and project management work
- Organize the deliverables into a logical hierarchy
- Decompose upper-level deliverables into lower-level components
- Assign identification codes (WBS numbering system)
- Verify completeness using the 100% Rule
Decomposition Guidelines
| Guideline | Explanation |
|---|---|
| Deliverable-oriented | WBS elements represent deliverables, not activities |
| 100% Rule | Each level must represent 100% of the parent level |
| Mutually exclusive | No overlap between WBS elements at the same level |
| Appropriate detail | Decompose to the work package level (smallest deliverable) |
| 8/80 Rule | Work packages should take 8 to 80 hours (some orgs use 4/40) |
The WBS Dictionary
The WBS dictionary is a companion document that provides detailed descriptions of each WBS element:
| Field | Description |
|---|---|
| WBS Code | Unique identifier for each element |
| Work Description | Detailed description of the work |
| Responsible Organization | Who performs the work |
| Milestones | Associated milestones |
| Schedule Activities | Linked activities |
| Resources Required | Resources needed |
| Cost Estimates | Estimated costs |
| Quality Requirements | Quality standards |
| Acceptance Criteria | How completion is verified |
| Technical References | Related technical documents |
| Assumptions and Constraints | Relevant assumptions and limitations |
From Work Packages to Activities
Work packages (lowest WBS level) are decomposed further into activities during schedule planning:
WBS → Work Packages → Activities → Schedule
| Concept | Level | Purpose |
|---|---|---|
| WBS Element | Deliverable hierarchy | Organize scope |
| Work Package | Lowest WBS level | Smallest deliverable unit |
| Activity | Below work packages | Smallest schedulable unit |
| Milestone | Key event | Zero-duration marker |
Activity Attributes
Each activity has attributes that describe it in detail:
- Activity ID and name
- Predecessor and successor activities
- Logical relationships and dependencies
- Leads and lags
- Resource requirements
- Imposed dates (constraints)
- Geographic location (if relevant)
Rolling Wave Planning
Rolling wave planning is a form of progressive elaboration where:
- Near-term work is planned in detail (at the activity level)
- Future work is planned at a higher level (work packages or planning packages)
- As the project progresses, future work is elaborated into detailed activities
This approach is useful when:
- The full scope cannot be defined in advance
- Requirements for later phases depend on results of earlier phases
- The project is long-term and future conditions are uncertain
Key Point: Rolling wave planning is NOT scope creep. It is a planned approach to elaborating detail as more information becomes available. The total scope (as captured in the WBS at a high level) remains controlled.
Milestone Lists
A milestone is a significant point or event in the project with zero duration. It marks the completion of a key deliverable or phase.
Types of Milestones
- Mandatory milestones: Required by contracts, regulations, or organizational policy
- Optional milestones: Placed by the project team to monitor progress
- External milestones: Dependent on factors outside the project
Milestones are used in:
- Schedule planning and progress tracking
- Stakeholder reporting
- Phase gate reviews
- Contract payment triggers
The 8/80 Rule in WBS development suggests that work packages should:
Rolling wave planning is best described as:
What is the duration of a milestone?