Introduction
Non-functional requirements (NFRs) are critical to the success of any software project, yet are often overlooked or poorly defined. Having clear, measurable NFRs documented upfront prevents misunderstandings later in the development process. This article provides an overview of NFRs and a downloadable non-functional requirements template to help you define comprehensive non-functional criteria for your next software project.
What are Non-Functional Requirements?
Non-functional requirements describe how a system should behave and impose constraints on its implementation. They complement the functional requirements that define specific functions and features. Examples of common NFRs include:
- Performance – Such as response times, throughput, and latency.
- Scalability – Ability to handle increased load and data volume.
- Reliability – The probability of failure-free operation over time.
- Availability – The proportion of time the system is operational and accessible.
- Security – Resilience against unauthorised access and data loss.
- Maintainability – Effort required to locate and fix errors in the system.
- Usability – The quality of the user experience.
NFRs often get inadequate attention during requirements planning. However, overlooking them can lead to software that fails to meet customer expectations despite having all the desired functionality. NFRs directly impact user satisfaction and should be considered early on.
Best Practices for Defining NFRs
Follow these tips to create meaningful, testable NFRs:
- Involve multiple stakeholders – Include input from users, project sponsors, architects, operations staff, etc. Different viewpoints ensure NFRs cover the full range of quality attributes.
- Make them specific and measurable – NFRs like “high performance” or “easy to use” are vague. Define concrete metrics like response time under X load or the number of clicks to complete a task.
- Set target values – Simply stating NFRs as objectives isn’t enough. Determine acceptable thresholds like 99.9% uptime or 500 concurrent users.
- Prioritise appropriately – Major NFRs like security deserve more focus than minor ones like look and feel. Clarify priorities upfront.
- Track NFRs separately from functional requirements – Maintain them as a distinct document for better visibility.
- Revisit and update as needed – Review NFRs during system architecture and design activities and refine as new information emerges.
Here you can view a comprehensive example list of NFRs and also some excellent examples in this glossary.
Non-Functional Requirements Template
The sample NFR template below can serve as a starting point for your projects. Tailor it to include the specific NFR categories that matter for your system and stakeholders.
- Project: [Project Name]
- Date: [Date Created]
- NFR Category: [Performance, Scalability, etc.]
- Requirement: [Specific NFR]
- Metric: [Quantitative measure for testing]
- Target Value: [Threshold or benchmark to meet]
- Priority: [High/Medium/Low]
- Notes: [Additional details]
Benefits of a Detailed NFR Template
Investing time upfront to develop a comprehensive, well-structured NFR template provides multiple advantages:
- Sets clear expectations between project team, sponsors, and users
- Drives design decisions and identifies necessary infrastructure/architecture
- Provides measurable targets for quality assurance testing
- Reduces risk of poor system performance or user experience
- Improves development process by identifying non-functional criteria early
- Facilitates trade-off analysis when NFRs conflict.
Recap
In summary, non-functional requirements have a huge impact on software quality and user satisfaction. Leveraging a template to define detailed, testable NFRs is a best practice that leads to better project outcomes. The free template provided here can get you started drafting NFRs tailored to your next project. Be sure to involve stakeholders, set quantitative metrics, and revisit NFRs throughout development to build software that meets business and user needs.