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
WBS, Work Packages, and Activity Definition
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?