Dependency
A dependency describes how two activities are linked so that one must start or finish before, after, or with the other; it sets the required order and timing between a predecessor and a successor.
Key Points
- Four patterns describe timing: finish-to-start (FS), start-to-start (SS), finish-to-finish (FF), and start-to-finish (SF).
- Origins include mandatory (hard), discretionary (preferred/soft), external, and internal dependencies.
- Leads and lags adjust overlap or waiting time between linked activities without changing the underlying logic.
- See logical relationship.
Example
In a construction project, "Frame walls" cannot begin until "Foundation cured" is complete, plus a 2-day wait for curing. This is an FS dependency with a 2-day lag.
PMP Example Question
Activity B must wait until Activity A finishes, and then there is a planned 2-day curing period before B can start. What best describes this relationship?
- Finish-to-Start with a 2-day lag
- Start-to-Start with a 2-day lead
- Finish-to-Finish with a 2-day lag
- Discretionary internal dependency with a lead
Correct Answer: A — Finish-to-Start with a 2-day lag
Explanation: B can start only after A has finished, and a waiting period is inserted; that is an FS relationship with lag.
