Imagine you're about to download a new mobile app that promises to revolutionize your daily routine. What do you expect from this app? Do you want it to be lightning-fast, secure, and reliable? Can you easily navigate its features and functionality? And what if you encounter any issues – how quickly can they be resolved?

These questions highlight the importance of nonfunctional requirements (NFRs) in software development. NFRs are specifications that describe a system's operation capabilities and constraints, ensuring it meets users' needs and expectations.

What Are Nonfunctional Requirements?

In essence, NFRs are quality attributes or software quality requirements that outline how well a product operates. These include factors like speed, security, reliability, data integrity, and more. While they may not directly describe the system's primary function, they're crucial in delivering an exceptional app user experience.

Functional vs Nonfunctional Requirements

In software engineering, there are two main categories of requirements: functional and nonfunctional. Functional requirements define what a software product must do – its features and functions. For instance, a messenger app's functional requirement might be to allow users to edit messages after sending them.

On the other hand, nonfunctional requirements specify how well a system must perform. Continuing with our messaging platform example, an NFR could be the speed at which the system updates message edits for all users in a chat within 0.1 seconds, assuming all users are online and have a strong LTE connection.

Software Documentation: A Foundation for Nonfunctional Requirements

All solution requirements are typically documented in software requirements specifications (SRS) and product requirements documents (PRD). These documents contain descriptions of functions and capabilities, as well as constraints and assumptions. By understanding the importance of NFRs, you can develop a comprehensive approach to software documentation.

Main Types of Nonfunctional Requirements

The most common categories of NFRs include:

  • Performance: How fast does the system return results?
  • Scalability: How much will performance change with higher workloads?
  • Portability: Which hardware, operating systems, and browsers does the software run on?
  • Compatibility: Does the system conflict with other applications and processes?
  • Reliability: How often does the system experience critical failures?
  • Maintainability: How much time does it take to fix an issue when it arises?
  • Availability: How long is the average system downtime?
  • Security: How well are the system and its data protected against attacks?
  • Usability: How easy is it to use the system?

Performance Requirements: A Crucial NFR

Performance requirements define how fast a software system responds to certain users' actions under a certain workload. This metric explains how long a user must wait before the target operation happens, given the overall number of users at the moment.

Examples of performance requirements include:

  • The landing page supporting 5,000 users per hour must provide a 6-second or less response time in a Chrome desktop browser.
  • Product search results should be displayed within 3 seconds for 90% of searches under normal conditions.
  • The system must be capable of ingesting data streams at a minimum rate of 1 million records per minute from various sources without loss of data.

How to Approach Performance Requirements

To develop an effective performance strategy, start by considering Google's recommendations for regular web pages. By focusing on delivering exceptional app user experience through NFRs, you can create a system that meets users' needs and expectations.