How to capture non-functional requirements?

Capturing non-functional requirements (NFRs) effectively is crucial for ensuring that a system meets not just its functional needs but also its operational quality and user expectations. Non-functional requirements address aspects such as performance, security, usability, and reliability, which are essential for a successful system deployment and operation. Here are systematic steps and best practices for capturing non-functional requirements:

1. Stakeholder Interviews

• Identify Stakeholders: Begin by identifying all relevant stakeholders, including end-users, project managers, business owners, developers, and operational staff.
• Conduct Interviews: Interview stakeholders to gather insights into their expectations and concerns regarding the system's operation. Each stakeholder group may have different priorities and perspectives on non-functional aspects.

2. Questionnaires and Surveys

• Deploy questionnaires and surveys to a broader audience to collect quantitative data on user expectations and needs concerning performance, usability, accessibility, etc. This method can be particularly useful in gathering large amounts of data efficiently.

3. Workshops

• Organize structured workshops that involve interactive sessions with multiple stakeholders. Use techniques such as brainstorming, scenario analysis, and role-playing to extract and understand their non-functional requirements.
• Utilize Templates: Use standardized templates like the FURPS model (Functionality, Usability, Reliability, Performance, and Supportability) to guide discussions and ensure comprehensive coverage.

4. Document Analysis

• Review existing documentation and systems to identify non-functional requirements that are currently being met or are lacking. This includes business plans, market research, user manuals, and compliance documents.

5. Use Cases and User Stories

• Develop detailed use cases and user stories that include non-functional criteria. For example, a user story might specify that a web page must load within two seconds, or that the system must handle a specific number of transactions per hour.

6. Benchmarking

• Look at industry standards and competitors to benchmark non-functional expectations. Understanding how similar systems perform can help in setting realistic and competitive non-functional goals.

7. Performance Metrics

• Define specific metrics and KPIs (Key Performance Indicators) for each non-functional requirement. This step is crucial for making the requirements measurable and testable.

8. Prioritization

• Not all non-functional requirements are equally important, and resources are typically limited. Prioritize NFRs based on business impact, user impact, and technical risk.

9. Specification and Documentation

• Clearly document the captured non-functional requirements. Each NFR should be specified in a way that is clear, measurable, and testable.
• Maintain a Living Document: Non-functional requirements may evolve based on new insights, technology changes, or business shifts. Regularly update the documentation to reflect these changes.

10. Review and Validation

• Regularly review the non-functional requirements with stakeholders to ensure they still meet the business and user needs.
• Validate assumptions through prototypes or technology proofs of concept to ensure feasibility.

Conclusion

Capturing non-functional requirements is a critical process that requires active engagement with stakeholders, systematic analysis, and continuous validation. Properly defined and managed NFRs ensure that the system not only functions as intended but also meets performance standards, operational efficiency, and user satisfaction. By integrating these practices into the early stages of system development, teams can avoid costly reworks and ensure a higher quality product.