Functional & Non-Functional Requirements
Functional & Non-Functional Requirements are a hot and catchy topics in Business Analysis knowledge that every BA should master on it.
🔧 Functional Requirements (FR)
These define what the system should do — the specific behaviors, functions, and data interactions.
📌 Characteristics:
- Describe tasks, services, or functions the system must perform.
- Based on stakeholder needs and business rules.
- Often captured as use cases, user stories, or process flows.
✅ Examples:
- The system shall allow users to log in using a username and password.
- The system shall generate a monthly financial report.
- The application shall send an email confirmation after user registration.
🧩 Non-Functional Requirements (NFR)
These define how the system performs or constraints on the functionality — often called quality attributes.
📌 Characteristics:
- Define system performance, usability, security, reliability, etc.
- Usually measurable or verifiable through benchmarks or testing.
✅ Examples:
- The system shall support 1,000 concurrent users without performance degradation.
- The application shall be available 99.9% of the time.
- All user data shall be encrypted at rest and in transit.
- The system shall load the dashboard within 2 seconds.
🆚 Key Differences
| Aspect | Functional Requirements (FR) | Non-Functional Requirements (NFR) |
|---|---|---|
| Focus | What the system does | How the system behaves |
| Type | Behavior, features, services | Quality, constraints, performance |
| Measurement | Pass/fail based on function execution | Often measured by performance metrics |
| Expression | Use cases, business rules, workflows | SLAs, performance thresholds, compliance rules |
🧠 Understanding Non-Functional Requirements (NFRs) Through Language
Non-Functional Requirements describe the qualities or attributes of a system. Etymologically, many of these qualities derive from Latin and are structured using suffixes like “-ability”, “-ity”, “-ence”, and “-ness”. These suffixes help define how well a system performs, rather than what it does.
📝 Common Suffixes in NFR Terminology
🔤 Suffix “-ability” – The capacity to be or do something
Derived from Latin -abilitas, this suffix is central to many NFR terms:
| Term | What It Represents | Example Requirement |
|---|---|---|
| Availability | Uptime and accessibility of the system | “System must operate 24/7 with 99.95% uptime.” |
| Scalability | Ability to grow and handle increasing demand | “System must support 10x growth in user volume.” |
| Reliability | Consistency and dependability of system performance | “System should not fail more than once per 10,000 operations.” |
| Usability | Ease of use and learnability for users | “System must allow task completion in under 3 clicks.” |
| Maintainability | Ease with which the system can be updated or repaired | “Bug fixes must be deployable within 2 hours.” |
| Portability | Ability to function across environments/platforms | “Application must run on both Android and iOS.” |
| Extensibility | Capacity to add new features without major redesign | “System must allow for plugin architecture.” |
🌀 Suffix “-ity” – A state or condition of being
Often used to describe inherent or emergent system properties:
| Term | What It Represents | Example Requirement |
|---|---|---|
| Security | Protection against unauthorized access or data loss | “All sensitive data must be encrypted in transit and at rest.” |
| Integrity | Accuracy and trustworthiness of data and systems | “Financial transactions must be tamper-proof.” |
| Flexibility | Ability to adapt to new requirements or conditions | “User workflows should be customizable per department.” |
| Complexity | Degree of intricacy or difficulty in use or maintenance | “System complexity must be kept under 5 modules per feature.” |
🌐 Suffix “-ence” / “-ency” – Ongoing state or quality
These reflect enduring qualities or system tendencies:
| Term | What It Represents | Example Requirement |
|---|---|---|
| Resilience | Ability to recover from failures or disruptions | “System must auto-recover within 30 seconds of failure.” |
| Efficiency | Optimal use of resources (time, memory, etc.) | “System must complete report generation in under 2 seconds.” |
| Transparency | Openness and auditability of processes | “All user actions must be logged and traceable.” |
| Consistency | Uniformity across operations and outputs | “Reports generated must match backend data 100% of the time.” |
🧭 The Big Picture
While Functional Requirements answer “What will the system do?”, Non-Functional Requirements focus on “How well will it do it?” — and the language used to describe them points directly to quality attributes that are measurable, testable, and critical for long-term success.
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