Nonfunctional Requirements — The Secret Sauce of a Successful Project Delivery

Throughout the application development process, to build an architecture optimized for achieving business goals while keeping future needs in sight, developers and other project stakeholders must take diverse considerations into account. Nonfunctional requirements (NFRs) are an essential element of this conversation.

NFRs are specifications that define how a system should operate. They cover key aspects like speed, security, reliability and data integrity. Often called quality attributes or software quality requirements, NFRs outline various elements of the system’s performance and functionality.

Although NFRs are crucial for a product’s success, developers and project stakeholders can easily overlook them. Let’s dive into the role of NFRs and their significance in any application development project.

Functional vs. Nonfunctional Requirements

Functional requirements specify the actions a system should perform, while nonfunctional requirements address how well it performs those actions. Even if the system falls short of meeting nonfunctional expectations, it can still achieve its primary purpose. For example, when you click on a Google search result, the functional requirement ensures you see the loaded page, while the nonfunctional aspect focuses on the speed at which it loads.

Different Types of Nonfunctional Requirements

NFRs are determined and agreed upon based on a project’s overall requirements. While there may be numerous NFRs to consider from project to project, here we’ll overview the most significant examples.

Scalability

Scalability is a measure of a system’s ability to handle workload fluctuations. When a developer is building a product, two key questions from a scalability perspective are: (a) How many users will be using my product? and (b) How many concurrent users will I have? Once the developer knows how many users the product needs to accommodate, the next step is to decide on the scaling strategy: horizontal or vertical. Choosing the right scaling strategy is key to ensuring a site can handle the workload without crashing.

Key success metrics: Total users, concurrent users, time taken to scale

Performance

The performance of a software architecture is measured primarily around the response time and throughput. The faster the response time with qualitative and high throughput, the better the performance. However, the degree of latency — the slowness in response time — deemed acceptable needs to be determined as well. The system might operate smoothly under certain loads, but when the workload increases, performance parameters could deteriorate. To ensure high performance of the system, stakeholders should capture clear benchmarks around the performance metrics during the requirement-gathering phase. Then the developers can design the application keeping these requirements, along with scalability options, in mind to avoid performance bottlenecks due to resource constraints.

Key success metrics: Response time, throughput

High availability

Availability refers to how accessible and operational an application is. High availability means the application is available 24/7, 365 days a year. It is quantified as a percentage representing the application’s uptime. A robust architecture is essential for meeting this NFR. For instance, Amazon uses several built-in features — elastic load balancing, availability zones and autoscaling— to achieve high availability.

Key success metric: Uptime

Security

Hackers can exploit system vulnerabilities, resulting in data theft. This NFR focuses on securing user data stored by applications against breaches. Following the 2024 OWASP Top 10 Proactive Controls can establish a foundational security culture for your application and organization, guiding early-stage software development toward building secure applications effectively. Thorough security testing using tools such as Burp Suite and Qualys can help detect any open vulnerabilities.

Key success metric: A GREEN security scan report

Localization

This NFR deals with how the application aligns itself with the local language, laws and other aspects — right-to-left screen display for Arabic languages, for example, and date formats tailored to geographic regions. Though often overlooked, localization can significantly influence how users perceive the product.

Key success metric: Adherence to all identified parameters captured via market research

Accessibility

People with a wide range of disabilities, including visual, auditory, physical, speech and cognitive, use websites. This NFR requires adherence to the Web Content Accessibility Guidelines (WCAG) to ensure web content is accessible to them.

Key success metric: GREEN Signal post-testing that ensures the application is operable, perceivable, robust and understandable

Mitigating Business and User-Interest Loss

Consider a case where you have kick-started a fixed-bid project to develop an iOS app for a client. All the technical specifics about the app’s features had been discussed, but not the NFRs.

The app development runs smoothly. However, a version update implemented during the user acceptance testing (UAT) phase resulted in the mobile app acting randomly for some features. The client expects you to resolve the issue (without additional payment); you believe it should be treated as a change request because the version upgrade case was not initially scoped or estimated.

Clearly, no alignments were made with the client during the discovery phase of the project regarding the version upgrade as an NFR. In 99 out of 100 cases, the development duration exceeds the original estimates, causing conflicts between the client and the delivery team regarding who should bear the additional costs.

This example highlights the importance of agreeing upon the NFRs from the outset. When managed effectively, these requirements prevent any loss to business, user interest and credibility.

The Right Stage to Capture NFRs

The business analyst on the project should capture NFRs during the discovery stage. Sometimes these details are missed because the client is not aware of the relevant questions to answer or assumes that the NFRs will be captured and delivered naturally.

Agreement on NFRs: Who Should Be Involved?

The agreed upon NFRs should be shared with all client stakeholders. These stakeholders may include those accountable for design, performance, security and accessibility, among others. It is essential for the business analyst to ensure that agreement on NFRs is reached prior to the start of the development phase.

Timely estimates and consideration of NFRs enable successful project deliveries without additional costs or delays.

Partner with Material for Successful and Secure Application Development

At Material, we prioritize security from the outset. Regardless of whether security is specified as an NFR, we incorporate it into our product backlog. Following OWASP guidelines is a standard part of our development process, ensuring thorough security testing before software is handed over to customers for UAT. If you need assistance with NFRs or any other project delivery needs, reach out to connect with our expert team today.