Finish-Start Logical Relationship: The Most Critical Dependency in Project Scheduling

PMBOK v8 Definition

A finish-to-start (FS) logical relationship is a dependency in which a successor activity cannot start until a predecessor activity has finished. According to PMBOK v8, this is the most commonly used type of precedence relationship in the precedence diagramming method (PDM). For example, installing the operating system on a PC (successor) cannot start until the PC hardware is assembled (predecessor).

This relationship belongs to the Sequence Activities process, which is part of the Planning Process Group and the Schedule Management Knowledge Area.

Why It Matters for the Exam

The FS relationship appears frequently on the PMI exam because it represents the default dependency type in project scheduling. Questions test your ability to identify the correct logical relationship type, understand its application in network diagrams, and recognize when other relationship types (FF, SS, SF) are more appropriate. Expect questions in both situational scenarios and direct definition-based items.

Key Points to Remember (for the exam)

• Most Common Type: FS is the most frequently used precedence relationship in project schedule network diagrams
• Default Assumption: When a dependency is described without specifying the type, PMI assumes it is FS
• Network Diagram Rule: Every work package and activity, except for the first and last, must be connected to at least one predecessor and one successor with an appropriate logical relationship
• Lead/Lag Application: FS relationships may require lead time (overlap) or lag time (delay) to create a realistic schedule
• Closed Loops: Closed loops in logical relationships are not recommended
• Multiple Relationships: Two activities can have two logical relationships simultaneously (e.g., SS and FF), but this is not recommended—select the relationship with the highest impact
• Key Benefit: Defining logical relationships determines the logical sequence of work to obtain the greatest efficiency given all project constraints

Typical PMI Exam Example

A construction project requires that concrete foundation curing be completed before framing can begin. The project manager documents this as a finish-to-start relationship with a 7-day lag to account for curing time. On the network diagram, this appears as: "Foundation Curing (FS + 7 days) → Framing."

PMI Exam Traps

• Trap: Confusing FS with SS (start-to-start)

  • Reality: FS requires the predecessor to finish completely; SS only requires the predecessor to start

• Trap: Thinking all dependencies are FS

  • Reality: PMBOK v8 defines four types: FS, FF, SS, and SF. Always verify which relationship the scenario describes

• Trap: Ignoring lead/lag in FS relationships

  • Reality: FS with lag (delay) means a waiting period; FS with lead (negative lag) means overlap is allowed

• Trap: Assuming activities without explicit connections are independent

  • Reality: Every activity except first and last must have at least one predecessor and one successor

Important PMI Connections

Quick Review Questions

1. In a project schedule network diagram, which logical relationship type is most commonly used and considered the default?

2. A project manager documents that "Testing cannot begin until Development is 100% complete." What type of logical relationship is this?

3. Every activity in a project schedule network diagram, except the first and last, should be connected to at least how many predecessor and successor activities?

4. Two activities have both an SS and an FF relationship simultaneously. According to PMBOK v8, what should the project manager do?

5. What is the key benefit of defining logical relationships such as FS in the Sequence Activities process?

PMBOK v8 Reference

Section 5.13 - Precedence Diagramming Method Relationship Types Section 4.2 - Project Schedule Network Diagram Section 5.0 - Sequence Activities Process (Planning Process Group, Schedule Management Knowledge Area)