Precedence Diagramming Method: FS, SF, SS, and FF Relationships
PMBOK v8 Definition
The Precedence Diagramming Method (PDM) defines four logical relationship types between project activities. Finish to Start (FS) is a logical relationship where a successor activity cannot start until a predecessor activity has finished. Start to Finish (SF) is a logical relationship in which a predecessor activity cannot finish until a successor activity has started. Start to Start (SS) is a logical relationship where a successor activity cannot start until a predecessor activity has started. Finish to Finish (FF) is a logical relationship where a successor activity cannot finish until a predecessor activity has finished.
Why It Matters for the Exam
These four relationship types are foundational to schedule development and appear frequently in PMI exam questions testing your ability to interpret network diagrams, calculate float, and identify dependency logic. Questions typically present a scenario requiring you to select the correct relationship type or identify which relationship is most commonly used versus rarely used.
Key Points to Remember (for the exam)
- Most Common Relationship: FS (Finish to Start) is the most commonly used type of precedence relationship in the precedence diagramming method
- Rarest Relationship: SF (Start to Finish) is very rarely used, but it is included to present a complete list of relationship types
- Multiple Relationships: Two activities can have two logical relationships at the same time (for example, SS and FF)
- Not Recommended: Multiple relationships among the same activities are not recommended; a decision has to be made to select the relationship with the highest impact
- Closed Loops: Closed loops are not recommended in logical relationships
- FS Example: Activity A must finish before Activity B can start (standard sequential work)
- SF Example: A new accounts payable system (successor) has to start before the old accounts payable system can be shut down (predecessor)
Typical PMI Exam Example
A construction project requires that the concrete foundation (Activity A) must be completely cured before the framing (Activity B) can begin. Which logical relationship describes this dependency? The answer is Finish to Start (FS) because the successor cannot start until the predecessor has finished.
PMI Exam Traps
- Trap: Confusing FS with SS when both activities can start simultaneously
- Reality: FS requires the predecessor to finish first; SS allows both to start at the same time
- Trap: Thinking SF is commonly used because it appears in the list
- Reality: SF is very rarely used; FS is the most commonly used relationship
- Trap: Assuming multiple relationships between two activities are always acceptable
- Reality: Multiple relationships are not recommended; select the relationship with the highest impact
- Trap: Believing closed loops are valid in logical relationships
- Reality: Closed loops are not recommended in logical relationships
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Activity A | Predecessor activity | Identifies which activity comes first in the relationship |
| Activity B | Successor activity | Identifies which activity depends on the predecessor |
| Network Diagram | Output of PDM | Relationships determine the sequence and critical path |
| Predictive Analytics | Tool for analysis | Used to analyze relationship impacts on schedule |
Quick Review Questions
- Which precedence relationship type is most commonly used in the precedence diagramming method?
- In an SF relationship, can the predecessor activity finish before the successor activity has started?
- What is the recommended action when two activities have multiple logical relationships at the same time?
- Give an example of an SF relationship from the PMBOK v8 content.
- Why are closed loops not recommended in logical relationships?
PMBOK v8 Reference
Section 5 – Tools and Techniques, Figure 5-13. Precedence Diagramming Method Relationship Types (Page 185-186)