Activity Dependencies and Resource Application
PMBOK v8 Definition
Activity dependencies are logical relationships between project activities that can affect the application and use of resources. These dependencies determine which activities should be completed before others can begin, using relationships such as start-to-start, finish-to-finish, start-to-finish, and finish-to-start. The project team determines which dependencies are discretionary or mandatory during the process of sequencing the activities, ensuring every work package and activity (except first and last) connects to at least one predecessor and one successor activity.
Why It Matters for the Exam
This concept appears frequently in PMI exam questions about Schedule Management and Resource Management, particularly in scenarios testing your ability to identify dependency types and their impact on resource allocation. Questions often present project situations where you must determine whether dependencies are mandatory, discretionary, external, or internal, and how these dependencies affect resource availability and scheduling decisions.
Key Points to Remember (for the exam)
- Mandatory Dependencies: Required by contract or physical/technical limitations (hard logic)
- Discretionary Dependencies: Determined by the project team based on best practices or preferred sequence (soft logic)
- External Dependencies: Relationship between project activities and non-project activities, usually outside the project team's control
- Internal Dependencies: Relationship between two project activities within the project team's control
- Path Convergence: Activity with multiple predecessor activities (higher risk due to multiple dependencies)
- Path Divergence: Activity with multiple successor activities (higher risk due to affecting multiple activities)
- Logical Relationships: Finish-to-Start (most common), Start-to-Start, Finish-to-Finish, Start-to-Finish
Typical PMI Exam Example
A software development project requires external hardware delivery before testing can begin. The testing activity depends on hardware from an external supplier. This is an external dependency because it involves a relationship between a project activity (testing) and a non-project activity (hardware delivery from an external source). The project management team has no control over the delivery schedule.
PMI Exam Traps
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Trap: Confusing mandatory dependencies with external dependencies
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Reality: Mandatory dependencies are required by contract or physical limitations; external dependencies involve non-project activities (which may also be mandatory or discretionary)
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Trap: Assuming all dependencies are mandatory
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Reality: The project team determines which dependencies are discretionary during the process of sequencing activities; not all dependencies are fixed
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Trap: Ignoring path convergence and divergence risks
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Reality: Activities with convergence or divergence are at greater risk because they are affected by or can affect multiple activities
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Trap: Thinking external dependencies are always outside the project
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Reality: External dependencies are specifically relationships between project activities and non-project activities, not just any outside factor
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Activity Attributes | Input to sequencing | Attributes include predecessor/successor activities, logical relationships, leads/lags, and resource requirements |
| Resource Breakdown Structure | Resource planning | Dependencies affect resource application; RBS categorizes resources by type (labor, materials, equipment, supplies) |
| Resource Calendar | Scheduling | Dependencies determine when resources are needed; resource calendar identifies working days and shifts for each specific resource |
| Leads and Lags | Scheduling technique | May be necessary between activities to support a realistic and achievable project schedule |
Quick Review Questions
- During the sequencing of activities, who determines which dependencies are discretionary?
- What is the key difference between an external dependency and an internal dependency?
- Why are activities with path convergence or divergence considered at greater risk?
- What logical relationship should connect every work package and activity (except first and last)?
- How do activity dependencies affect the application and use of resources?
PMBOK v8 Reference
Section 6.3 - Sequence Activities (Process Group: Planning, Knowledge Area: Schedule Management)
The project team determines dependencies during the sequencing process, categorizing them as mandatory, discretionary, external, or internal. Every activity must be connected with appropriate logical relationships to create a realistic project schedule, considering leads and lags as necessary. Activities with multiple predecessors (convergence) or multiple successors (divergence) require special attention due to increased risk.