What are non-functional requirements in usability?

Non-functional requirements (NFRs) related to usability are critical aspects that define the quality of the user experience in interacting with a system or product. Usability itself is a broad category under non-functional requirements that ensures the system is user-friendly, efficient, and satisfying to use. When specifically focusing on usability as a non-functional requirement, it encompasses several key elements that contribute to how easily and effectively users can achieve their goals with a product. Here are the primary non-functional requirements associated with usability:

1. Learnability

• Definition: How easy it is for users to accomplish basic tasks the first time they encounter the design.
• Example: New users should be able to navigate through the main functions of an application and perform basic operations like creating an account or uploading a document within a few minutes of introduction.

2. Efficiency

• Definition: Once users have learned the design, how quickly can they perform tasks?
• Example: A frequent user should be able to complete a data entry form or make a purchase with minimal steps and interruptions.

3. Memorability

• Definition: When users return to the design after a period of not using it, how easily can they reestablish proficiency?
• Example: Users who have not used the application for a month can come back and remember how to perform tasks without having to relearn everything.

4. Errors

• Definition: How many errors do users make, how severe are these errors, and how easily can they recover from the errors?
• Example: The system should provide informative error messages and quick recovery options, allowing users to easily correct mistakes when filling out forms or navigating through the application.

5. Satisfaction

• Definition: How pleasant is it to use the design?
• Example: User satisfaction surveys or feedback mechanisms indicate that users enjoy using the system and feel positive about their interactions.

6. Accessibility

• Definition: How accessible is the product to people with a wide range of abilities and disabilities?
• Example: The product must comply with accessibility standards such as WCAG (Web Content Accessibility Guidelines) to ensure that all users, including those with disabilities, can use the product effectively.

7. Aesthetic and Minimalist Design

• Definition: Interfaces should not contain information which is irrelevant or rarely needed. Every extra unit of information competes with the relevant units of information and diminishes their relative visibility.
• Example: The user interface should feature a clean design that emphasizes the most critical elements, minimizing clutter and distractions.

Importance of Usability as a Non-Functional Requirement

Usability is crucial because it directly impacts user effectiveness, efficiency, and satisfaction, which are essential for the success of any software product. Poor usability can lead to increased training and support costs, reduced productivity, and user frustration, which ultimately affects the adoption and success of the system.

Addressing usability in the design phase as a non-functional requirement helps ensure that the system will be more than just functional; it will also be user-friendly and conducive to a positive user experience. This is particularly important in competitive markets where user satisfaction can be a significant differentiator.