What are non-functional requirements in design?

Non-functional requirements (NFRs) in system design refer to criteria that specify how a system should behave and the qualities it must have. These requirements are not directly concerned with the specific functions or processes of the application (such as logging in, retrieving data, etc.), but rather with attributes related to the system’s performance, usability, reliability, and other operational characteristics. Understanding and incorporating NFRs are essential for ensuring that the system will perform well and meet user expectations in production.

Common Types of Non-Functional Requirements:

1. Performance Requirements:

   • Speed and Latency: How fast the system responds to user inputs or processes data.
   • Throughput: The amount of processing the system can handle in a given time period.
   • Capacity: The maximum load the system can handle without performance degradation.

2. Scalability:

   • Horizontal Scaling: Ability of the system to increase capacity by connecting multiple hardware or software entities so that they work as a single logical unit.
   • Vertical Scaling: Ability of the system to add resources to increase the capacity of existing hardware or software components.

3. Reliability:

   • Availability: The degree to which a system is operational and accessible when required for use. Often measured as a percentage of uptime.
   • Fault Tolerance: The system's ability to continue operating properly in the event of the failure of some of its components.

4. Maintainability:

   • Modifiability: Ease with which a system or component can be modified to correct faults, improve performance or other attributes, or adapt to a changed environment.
   • Manageability: How easily a system can be monitored, managed, and maintained over its lifetime.

5. Usability:

   • User Experience (UX): Encompasses all aspects of the end-user's interaction with the company, its services, and its products.
   • Accessibility: The degree to which a product or service is accessible by as many people as possible.

6. Security:

   • Confidentiality: Ensuring that information is accessible only to those authorized to have access.
   • Integrity: Safeguarding the accuracy and completeness of information and processing methods.
   • Authentication and Authorization: Processes that control who can access the system and what actions they are permitted to perform.

7. Compliance:

   • Regulatory Compliance: Adhering to laws, regulations, guidelines, and specifications relevant to its business processes.
   • Standards Compliance: Conforming to industry or technical standards that might apply to the system.

8. Portability:

   • Platform Independence: Ability of the system to run under different computing environments.
   • Interoperability: Ability of the system to interact and function with other independent systems.

9. Disaster Recovery:

   • Recoverability: Ability to recover from crashes, hardware failures, and other similar problems.
   • Data Integrity and Backup: Systems for ensuring that data remains accurate, consistent, and safe from loss or corruption.

Importance of Non-Functional Requirements:

NFRs are critical because they directly impact the user's experience and satisfaction with the system. They help ensure that functional aspects of the system are delivered with quality and that the system remains effective under varying conditions. Ignoring non-functional requirements can lead to systems that fail under stress or systems that are difficult to maintain, scale, or secure.

Conclusion:

Incorporating non-functional requirements into the design and development processes is crucial for building robust, efficient, and user-friendly systems. NFRs ensure that a system not only meets its functional requirements but also delivers performance, reliability, and operability that meets or exceeds stakeholders' expectations.