Nonfunctional Requirements: Performance, Security, and Operational Criteria

PMBOK v8 Definition

Nonfunctional requirements complement functional requirements by specifying performance, security, and operational criteria essential for product effectiveness and user satisfaction. Examples include reliability, security, performance, safety, level of service, supportability, retention/purge, etc. These requirements are a subgroup of solution requirements, which describe the features, functions, and characteristics of the product, service, or result that will meet business and stakeholder needs.

Why It Matters for the Exam

The PMI exam frequently tests the distinction between functional and nonfunctional requirements, as this differentiation is critical for scope definition, quality management, and stakeholder satisfaction. Questions appear in scope management, requirements gathering, and quality assurance contexts, often asking you to identify which type of requirement a given example represents.

Key Points to Remember (for the exam)

• Definition: Nonfunctional requirements specify how the product performs, not what it does
• Key Categories: Performance, security, reliability, safety, level of service, supportability, retention/purge
• Complementary Nature: They complement functional requirements; both are needed for complete solution requirements
• User Satisfaction Focus: Nonfunctional requirements directly impact user satisfaction and product effectiveness
• Measurable Criteria: Must be unambiguous (measurable and testable) to be baselined
• Common Confusion: Confusing nonfunctional requirements with functional requirements or business requirements
• Documentation: Recorded in requirements documentation and traceable via the requirements traceability matrix

Typical PMI Exam Example

A project manager is defining requirements for a new banking application. The stakeholder states the system must "process transactions within 2 seconds" and "maintain 99.99% uptime." These are nonfunctional requirements because they specify performance and operational criteria, not the behaviors or actions the product should execute.

PMI Exam Traps

• Trap: Confusing "data retention/purge" as a functional requirement Reality: Retention/purge is a nonfunctional requirement specifying operational criteria for data management

• Trap: Thinking nonfunctional requirements are optional or lower priority Reality: They are essential for product effectiveness and user satisfaction, equally important as functional requirements

• Trap: Assuming "security" is always a functional requirement Reality: Security is listed as a nonfunctional requirement example in PMBOK v8

• Trap: Confusing nonfunctional requirements with business requirements Reality: Business requirements describe stakeholder needs; nonfunctional requirements describe performance/security criteria

Important PMI Connections

Quick Review Questions

1. Which of the following is an example of a nonfunctional requirement: "The system must allow users to transfer funds" or "The system must process transfers within 1 second"?

2. What are the three main criteria that nonfunctional requirements specify according to PMBOK v8?

3. How do nonfunctional requirements differ from functional requirements in terms of what they describe?

4. Why must nonfunctional requirements be unambiguous (measurable and testable) before baselining?

5. In the requirements categorization hierarchy, where do nonfunctional requirements fit relative to business requirements and stakeholder requirements?

PMBOK v8 Reference

Section 5.2 - Collect Requirements (Requirements Documentation and Requirements Traceability Matrix)