5.4. Non-Functional Requirements (NFRs)

Requirements that define how the system should behave, focusing on system qualities and constraints rather than specific behaviors.

Non-Functional Requirements (NFRs) are essential aspects of system specifications that dictate how well a system performs rather than what it does specifically. While Functional Requirements outline the actions or tasks the system needs to perform, NFRs focus on the qualities of those functions. This includes considerations like how secure the system is, how fast it responds, and how easy it is to use.

Think of NFRs like the rules that govern a sporting event. For example, in basketball, the rules specify dimensions of the court and how long play can last (NFRs). While the players execute specific plays (functional requirements), it’s these governing rules that dictate how the game is conducted.

Key Characteristics: ● Quality-related (performance, security, usability, etc.) ● Often cross-cutting across many functional components ● Measurable or testable

NFRs share several key characteristics. They are primarily quality-related, meaning they describe the qualities the system must hold. They are often cross-cutting, affecting many functional areas of the system rather than being tied to a single function. Moreover, they are measurable or testable, which means you can evaluate whether or not the NFRs are met using concrete metrics.

Imagine you are cooking a dish where you want it to taste good (taste being an NFR). While the ingredients and recipe (functional requirements) determine how you prepare the dish, tasting and adjusting seasoning based on flavor (measurable quality) is akin to ensuring that your NFR is fulfilled.

Examples: ● The system should load the homepage in under 2 seconds ● The application must support 5,000 concurrent users ● Data should be encrypted in transit and at rest

Examples of NFRs highlight their diverse nature. For instance, requiring the system to load quickly (first example) targets performance, while supporting a large number of users (second example) emphasizes scalability. The third example ensures security by specifying that data is encrypted during transmission and storage. Each of these examples showcases how system qualities are essential to its overall functionality and user satisfaction.

Consider a theme park. The requirement for rides to accommodate thousands of visitors simultaneously (scalability) ensures everyone has the opportunity to enjoy the attractions. Quick waiting times (performance) enhance the visitor experience, just like how the encryption of personal data protects their privacy.

Types of NFRs: ● Performance (e.g., response time, throughput) ● Security (e.g., authentication, encryption) ● Usability (e.g., intuitive design, accessibility) ● Reliability (e.g., system uptime, error handling) ● Scalability (e.g., ability to grow with demand) ● Compliance (e.g., GDPR, HIPAA)

NFRs come in various types, each focusing on different aspects of system quality. Performance addresses how fast and efficiently a system operates. Security relates to how well user data is protected. Usability pertains to how user-friendly the system is. Reliability ensures the system is dependable. Scalability looks at how well the system can handle increased loads, and compliance ensures the system adheres to legal regulations. Each type plays an important role in fulfilling overall user and organizational requirements.

Think of a high-performance car as an analogy. The engine's response time and speed (performance) matter for racing. The brakes and safety features (security) ensure drivers are kept safe, while the dashboard interface (usability) must be intuitive for the driver. The car must also perform reliably over time (reliability) and be able to handle different conditions, like increased passenger weights (scalability), all while following automotive regulations (compliance).

Deliverables: ● NFR Documentation ● Service Level Agreements (SLAs) ● System Design Constraints

When working with NFRs, several key deliverables must be created. NFR Documentation is a detailed account of all NFRs outlined for the project. Service Level Agreements (SLAs) stipulate the expected service standards and responsibilities. System Design Constraints are restrictions or guidelines that will impact how the system is built and operate, ensuring that the NFRs can be achieved.

Consider building a custom home. The NFR Documentation would be like the blueprint that specifies quality and performance standards for materials. SLAs could represent contracts with builders detailing completion times and quality checks. System Design Constraints would involve zoning laws or budget limits that must be respected while building the house, ensuring that the final outcome meets the owner’s expectations for safety, comfort, and style.

BA's Role: ● Elicit NFRs through stakeholder interviews and system reviews ● Ensure NFRs are testable and documented ● Collaborate with architects and developers to plan for NFRs

The Business Analyst (BA) plays a crucial role when it comes to NFRs. They are responsible for gathering these requirements through discussions with stakeholders and analyzing the systems. Ensuring NFRs are testable means they are articulated in a way that allows for verification once the system is implemented. Finally, collaborating with architects and developers ensures that NFRs can be incorporated into the system's design.

Think of the BA as a project manager for a movie. They interview the cast and crew (stakeholders) to understand required performances and production values (NFRs). They need to ensure that all aspects — from acting, lighting, to special effects — are achievable and can be tested during production, ensuring the final movie meets quality standards before its release.

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