Dependency
DE: Abhaengigkeit
A logical relationship between two project activities.
Detailed Explanation
A dependency is a logical relationship between two activities that determines their sequence. The four types are: Finish-to-Start (FS) — the most common, where the successor starts after the predecessor finishes; Finish-to-Finish (FF); Start-to-Start (SS); and Start-to-Finish (SF) — the rarest.
Dependencies can be mandatory (hard logic, inherent in the work), discretionary (soft logic, based on best practices), external (involving factors outside the project), or internal (between project activities).
Understanding dependencies is essential for building the project network diagram, calculating the critical path, and identifying float. Incorrect dependencies lead to unrealistic schedules and missed deadlines.
Key Points
- Four types: FS (most common), FF, SS, SF (rarest)
- Mandatory (hard) vs. discretionary (soft) logic
- External vs. internal dependencies
- Essential for network diagrams and critical path analysis
- Modified by leads (overlap) and lags (delay)
- Incorrect dependencies create unrealistic schedules
Practical Example
In a house construction project: 'Pour foundation' must finish before 'Build walls' starts (FS mandatory). 'Install plumbing' and 'Install electrical' can start at the same time (SS discretionary). 'Order permits' depends on the city government (external). The PM maps all dependencies to build the network diagram.
Tips for Learning and Applying
Default to Finish-to-Start — it is the most intuitive and common
Question discretionary dependencies — they may unnecessarily constrain the schedule
Document all external dependencies and assign owners
Use leads and lags sparingly and only when they reflect reality
Related Terms
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