Network Diagrams and Dependencies
4
Dependency Types
FS, SS, FF, SF
2
Modifiers
Leads (overlap) and lags (delay)
2×2
Origin × Type
Mandatory/Discretionary × Internal/External
four types · but 95% of real life is FS
Four Dependency Types
how to read this
- › Each pair shows an arrow from one activity to another. The label tells you which ends of the activities are connected.
- › FS(default) reads "the finish of A connects to the start of B." You see this everywhere.
- › Leads let the successor start before the predecessor finishes (overlap, saves time, adds risk).
- › Lags delay the successor (cure time, cool-down, mandatory wait).
Exam Traps
FS is the default, SF is rarest
Finish-to-Start is the most common dependency. Start-to-Finish is unusual and the exam tests whether you know when to use it.
Mandatory dependencies are hard logic
You cannot pour concrete before the foundation is dug. That is mandatory. Discretionary is preferred practice, not physics.
External dependencies are outside project control
A permit from city hall, a vendor delivery — these are external dependencies. Manage by engaging the external party early.
FS default
Finish-to-Start is the standard. Use others only when the work actually requires them.
Lead is not lag
A lead lets successor start earlier. A lag delays it. Easy to confuse.
You must finish showering before you can get dressed. Classic FS.
You start the coffee and start feeding the cat at the same time. Both start together.
Writing the report and formatting the report finish together. Neither waits, but they end simultaneously.
The night shift cannot end until the day shift starts. Rare but real.
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