Mandatory Dependencies: Hard Logic in Project Schedule Management
PMBOK v8 Definition
Mandatory dependencies are those that are legally or contractually required or inherent in the nature of the work. These dependencies often involve physical limitations, such as on a construction project, where it is impossible to erect the superstructure until after the foundation has been built, or on an electronics project, where a prototype has to be built before it can be tested. Mandatory dependencies are sometimes referred to as hard logic or hard dependencies.
This concept belongs to the Schedule Management Knowledge Area within the Planning Process Group, specifically during the Develop Schedule process.
Why It Matters for the Exam
Mandatory dependencies appear frequently in PMI exam questions testing your ability to distinguish between dependency types. You will encounter scenario-based questions where you must identify whether a relationship between activities is mandatory, discretionary, external, or internal. The exam tests your understanding that mandatory dependencies are non-negotiable and driven by the nature of the work itself, not by preference or best practice.
Key Points to Remember (for the exam)
- Definition: Mandatory dependencies are legally or contractually required OR inherent in the nature of the work.
- Alternative Names: Also called hard logic or hard dependencies.
- Key Characteristic: Involves physical limitations that cannot be overcome.
- Common Examples: Foundation before superstructure (construction); prototype before testing (electronics); coding before testing (software).
- Source: The dependency is built into the work itself, not chosen by the project team.
- Critical Distinction: Unlike discretionary dependencies (soft logic), mandatory dependencies cannot be changed without changing the project scope or approach.
- Exam Tip: If a dependency is driven by a physical law, contract clause, or regulation, it is mandatory.
Typical PMI Exam Example
A construction project manager is developing the schedule. The project must pour concrete foundations before erecting steel beams. The contract specifies this sequence due to structural requirements. What type of dependency is this?
Answer: Mandatory dependency (hard logic), because it is inherent in the nature of the work and contractually required.
PMI Exam Traps
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Trap: Confusing mandatory dependencies with discretionary dependencies.
- Reality: Mandatory = required by law, contract, or physics; Discretionary = best practice or preference.
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Trap: Thinking all dependencies in a contract are mandatory.
- Reality: Only those dependencies that are inherent in the nature of the work or legally/contractually required are mandatory. Some contract dependencies may be external or discretionary.
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Trap: Assuming mandatory dependencies are always between physical tasks.
- Reality: They can also exist between non-physical activities (e.g., regulatory approval before market launch).
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Trap: Confusing mandatory dependencies with external dependencies.
- Reality: External dependencies involve parties outside the project team; mandatory dependencies are about the nature of the work, regardless of who performs it.
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Discretionary Dependencies | Opposite concept | Exam tests ability to distinguish: mandatory (hard logic) vs. discretionary (soft logic/preferred) |
| External Dependencies | Different category | External = outside project control; Mandatory = inherent in work nature (may be internal or external) |
| Develop Schedule Process | Where dependency is applied | Mandatory dependencies are identified and documented during schedule development |
| Project Schedule Network Diagrams | Output that shows dependencies | Mandatory dependencies create fixed sequence in network diagrams that cannot be reordered |
Quick Review Questions
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A software project requires that unit testing must follow code development. What type of dependency is this, and why?
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Your project has two activities: "Obtain building permit" and "Begin construction." The permit must be obtained before construction starts due to local regulations. Is this a mandatory or external dependency?
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A project manager discovers that a dependency between two activities can be reordered without violating any legal or physical requirements. What type of dependency is this NOT?
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On an aerospace project, the engine must be installed before the nacelle can be attached. Is this hard logic or soft logic? Explain.
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During schedule development, you identify a dependency that exists because of a contractual clause between your organization and a supplier. Is this automatically a mandatory dependency? Why or why not?
PMBOK v8 Reference
Section 5.8 (as referenced in the provided context) - Mandatory dependencies are defined in the context of Develop Schedule process, within the Schedule Management Knowledge Area. The exact definition appears in the context of Figure 5-8 Sample WBS With Major Deliverables, where mandatory dependencies are described as those "legally or contractually required or inherent in the nature of the work" involving physical limitations such as "impossible to erect the superstructure until after the foundation has been built" or "prototype has to be built before it can be tested."