Discretionary Dependencies: Preferred Logic in Activity Sequencing

PMBOK v8 Definition

Discretionary dependencies, also known as preferred logic, preferential logic, or soft logic, are dependencies established based on knowledge of good practices within a particular application area or some unusual aspect of the project where a specific sequence is desired, even though there may be other acceptable sequences. They are not mandatory; both activities may occur at the same time (in parallel); however, performing the activities in sequential order reduces the overall project risk. Discretionary dependencies are determined by the project team during the process of sequencing the activities.

Why It Matters for the Exam

This concept appears frequently in PMI exam questions about schedule development, specifically in questions testing your understanding of dependency types and their impact on float values. You will encounter it in situational questions where the project manager must decide whether to apply fast tracking or maintain sequential logic, and in definition-based questions distinguishing mandatory from discretionary dependencies.

Key Points to Remember (for the exam)

• Alternative Names: Discretionary dependencies are also called preferred logic, preferential logic, or soft logic
• Key Characteristic: They are NOT mandatory; other acceptable sequences exist
• Risk Impact: Performing activities in sequential order reduces overall project risk
• Documentation Requirement: Must be fully documented because they can create arbitrary total float values and limit later scheduling options
• Fast Tracking Consideration: When fast tracking is employed, discretionary dependencies should be reviewed and considered for modification or removal
• Determination Responsibility: The project team determines which dependencies are discretionary during the process of sequencing activities
• Common Example: During construction, electrical work should start after finishing plumbing work (generally accepted good practice, not mandatory)

Typical PMI Exam Example

A project manager is developing the schedule for a construction project. The team decides that plumbing work must finish before electrical work begins, based on industry best practices. However, both activities could technically be performed in parallel. The project manager documents this as a discretionary dependency. During schedule compression, the team reviews this dependency and considers whether to modify or remove it to enable fast tracking.

PMI Exam Traps

• Trap: Confusing discretionary dependencies with mandatory dependencies (hard logic)

  • Reality: Discretionary dependencies are based on preference/good practice; mandatory dependencies are legally or contractually required

• Trap: Assuming discretionary dependencies are always optional and can be ignored

  • Reality: They reduce risk and should be respected unless fast tracking requires modification

• Trap: Thinking discretionary dependencies have no impact on float

  • Reality: They can create arbitrary total float values and limit later scheduling options

• Trap: Confusing discretionary dependencies with external dependencies

  • Reality: External dependencies involve factors outside the project team's control; discretionary dependencies are internal team decisions

Important PMI Connections

Quick Review Questions

1. What are the three alternative names for discretionary dependencies in PMBOK v8?

2. Why must discretionary dependencies be fully documented?

3. What should be done with discretionary dependencies when fast tracking techniques are employed?

4. Who determines which dependencies are discretionary during activity sequencing?

5. What is the risk impact of performing activities in sequential order versus parallel when using discretionary dependencies?

PMBOK v8 Reference

Section 5 – Tools and Techniques (pages 167-168) - A Guide to the Project Management Body of Knowledge (PMBOK v8)