Functional and Non-Functional Requirements
✅ 1. What are Functional Requirements?
📌 Definition:
Functional Requirements describe what a system, product, or service should do. They define the specific behaviors, functions, and processes that the system must perform to meet business needs.
💡 Think of functional requirements as the "features and functions" of the system.
✅ Examples of Functional Requirements:
System Type
Functional Requirement Example
E-commerce Website
The system shall allow users to add products to a shopping cart.
Banking Application
The system shall enable users to transfer money between accounts.
HR Management System
The system shall allow HR managers to approve or reject leave requests.
CRM (Customer Relationship Management)
The system shall allow users to create and manage customer profiles.
✅ Characteristics of Functional Requirements:
Define specific functionality.
Focus on input, process, and output.
Directly related to user needs and business processes.
Often described using use cases, user stories, or functional specifications.
✅ 2. What are Non-Functional Requirements (NFRs)?
📌 Definition:
Non-Functional Requirements describe how a system should perform rather than what it should do. They specify the quality attributes, performance metrics, and constraints of the system.
💡 Think of non-functional requirements as "qualities" or "standards" the system must meet.
✅ Examples of Non-Functional Requirements:
Category
Non-Functional Requirement Example
Performance
The system shall handle up to 1,000 transactions per second.
Usability
The system shall be accessible to users with disabilities.
Reliability
The system shall have 99.9% uptime.
Security
The system shall encrypt all user data using AES-256.
Scalability
The system shall support scaling up to 10,000 concurrent users.
Maintainability
The system shall allow easy update and modification of business rules.
Compliance
The system shall comply with GDPR regulations.
✅ Characteristics of Non-Functional Requirements:
Define quality attributes (performance, usability, reliability).
Address system behavior under specific conditions.
Often expressed as measurable criteria.
Support and constrain functional requirements.
✅ 3. Difference between Functional and Non-Functional Requirements
Aspect
Functional Requirements
Non-Functional Requirements
Definition
Describe what the system must do.
Describe how the system should behave or perform.
Focus
Features and functionalities.
Performance, quality, constraints.
Example
"User can reset their password."
"Password reset process must complete within 5 seconds."
Form
Often use use cases, user stories, process flows.
Often use quality metrics, SLAs, benchmarks.
Relation to User Needs
Directly related to business tasks and user actions.
Related to user expectations, satisfaction, and compliance.
Testability
Tested through functional testing.
Tested through non-functional testing (performance, security).
✅ 4. How Business Analysts (BAs) Handle Functional and Non-Functional Requirements
Activity
BA Role
Requirement Elicitation
Identify both functional and non-functional needs through interviews, workshops, and document analysis.
Documentation
Clearly document functional requirements in use cases/user stories and non-functional requirements in quality standards/specifications.
Requirement Validation
Ensure that both types are reviewed and approved by stakeholders.
Requirement Prioritization
Prioritize functional and non-functional requirements based on business value and risk.
Requirement Traceability
Link both functional and non-functional requirements to business objectives and test cases.
✅ 5. Techniques for Defining Functional and Non-Functional Requirements
Technique
Purpose
Type
Use Cases / User Stories
Describe specific system interactions.
Functional
Process Modeling (BPMN, UML)
Visualize business and system processes.
Functional
Surveys and Questionnaires
Gather detailed user needs.
Both
Stakeholder Interviews
Understand explicit and implicit requirements.
Both
Prototyping/Wireframes
Visualize functionalities to clarify needs.
Functional
Quality Attribute Workshops
Identify quality standards (performance, security).
Non-Functional
NFR Catalog / Templates
Use structured templates for non-functional attributes.
Non-Functional
✅ 6. Example Combined Table of Functional & Non-Functional Requirements
Requirement ID
Requirement Type
Description
Priority
FR-001
Functional
System shall allow users to register new accounts.
High
FR-002
Functional
System shall enable users to reset passwords.
High
NFR-001
Non-Functional (Performance)
System shall respond to user actions within 2 seconds.
Medium
NFR-002
Non-Functional (Security)
System shall require multi-factor authentication for login.
High
NFR-003
Non-Functional (Usability)
System shall comply with WCAG 2.1 accessibility standards.
Medium
✅ 7. Why Understanding Both is Important?
Reason
Impact on Project
Complete System Design
Ensures that both functionality and performance expectations are addressed.
User Satisfaction
Meets not only what users want to do but how they experience it.
Compliance and Security
Avoids legal risks by meeting regulatory requirements.
System Sustainability
Prepares the system for future scaling and maintenance.
✅ 8. Conclusion
Aspect
Key Takeaway
Functional Requirements
Define what the system should do to meet business goals.
Non-Functional Requirements
Define how well the system should perform and behave under different conditions.
BA Role
Elicit, document, validate, and ensure traceability of both.
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