Dependency Types
Dependencies are the links that connect one project task to another — where the start or completion of one task depends on the start or completion of another. They are often the greatest single source of risk to a project.
Classification by control
- Internal dependencies — within the project, under your team’s control. Example: you wouldn’t tell a crew to get to work before the scope is defined and contracts are signed.
- External dependencies — reliant on outside factors (regulators, other projects). Example: a construction company waiting for city approval before demolition.
- Mandatory dependencies — legally or contractually required. Example: pouring and inspecting a concrete foundation before building on it.
- Discretionary dependencies — could occur independently, but the team chose to link them. Example: pouring a test portion of foundation from a new supplier to confirm total material needs before buying the rest.
The 4 relationship types
Every dependency is one of four relationships between two tasks:
| Type | Meaning | Everyday example |
|---|---|---|
| Finish → Start | Task A must finish before Task B starts | Finish putting on socks → Start putting on shoes |
| Finish → Finish | Task A must finish for Task B to finish | Finish making the icing → Finish decorating the cake |
| Start → Start | Task A must start for Task B to start | Start paying for train ride → Start boarding the train |
| Start → Finish | Task A must start for Task B to finish | Friend’s coworker starts shift → Friend finishes shift |
Finish → Start is by far the most common in project plans.
Dependency management (4 steps)
- Proper identification — brainstorm all possible dependencies and categorize them
- Recording — add them to the risk register with description, date, affected tasks
- Continuous monitoring & control — regular check-ins on interrelated tasks
- Efficient communication — keep team and stakeholders updated
Application
Identify dependencies during course-3-project-planning after the work-breakdown-structure is built. They feed the gantt-chart arrows and the critical-path-method analysis. Monitor them throughout course-4-project-execution — if one slips, everything downstream is at risk.
Connections
- work-breakdown-structure
- gantt-chart critical-path-method
- risk-management-process
- course-3-project-planning