Non-functional requirements, also known as “quality attributes,” are a crucial part of developing any successful product. Unlike functional requirements that define specific behaviors or features, non-functional requirements address broader quality characteristics that ensure a product is usable, performs well, is secure, and meets other critical quality standards. For product managers, properly identifying, prioritizing, and managing non-functional requirements is essential for delivering products that satisfy user needs and achieve business goals.
This blog post will provide an in-depth look at common types of non-functional requirements, methods for prioritizing them, and best practices for product managers to manage trade-offs and advocate for these “quality of service” needs throughout the product development lifecycle. Thoroughly understanding non-functional requirements will empower product managers to release products that go beyond functionality to provide exceptional user experiences.
Common Types of Non-Functional Requirements
There are many categories of non-functional requirements that product managers need to consider. Some of the most common include:
Performance – Performance requirements address how fast or responsive a product is. Example requirements might include page load times, transaction speeds, or frames per second for video. Performance is often measured through benchmarks and load testing. It’s important to set quantitative targets for critical performance criteria.
Security – Security encompasses requirements around access control, encryption, privacy, prevention of fraud or data loss, and resistance to hacking attempts. Security requirements help ensure sensitive user data is protected.
Reliability/Availability – Reliability refers to the likelihood a system will fail during normal operation. Availability measures the proportion of time a system is functional and working. Together, reliability and availability requirements aim to ensure a system is dependable and accessible when users need it.
Usability – Usability requirements relate to how easy and intuitive a product is to use. Specific metrics might include task success rate, time to learn, or subjective satisfaction ratings. Usability requirements are often validated through user testing and feedback.
Maintainability – Maintainability refers to how easy it is to update, fix, or enhance a product. Requirements might focus on modularity, coding standards, or complexity. This impacts the efficiency of maintenance work.
Prioritizing and Trade-Offs with Non-Functional Requirements
Not all non-functional requirements are created equal. Product managers need to work with stakeholders to prioritize which quality attributes are most important to focus on based on user needs, business goals, and technical or resource constraints.
Certain non-functional requirements may also conflict with each other, requiring trade-offs. For example, improving security often comes at the expense of usability. More stringent password rules and multi-factor authentication improve security but harm ease of use. Scaling systems to handle more users can reduce response times and performance for each user. Finding the right balance depends on the priorities of the product and input from users.
Some tips for prioritizing non-functional requirements:
- Identify must-have vs. nice-to-have quality attributes based on user research, customer feedback, and market analysis.
- Classify requirements as high, medium, or low priority based on business goals and tech constraints.
- Set measurable targets for the most critical non-functional requirements like performance speed.
- Be ready to reassess priorities when business goals or user needs evolve.
Eliciting and Documenting Non-Functional Requirements
To gather non-functional requirements, product managers should utilize techniques like:
- User surveys and support calls to identify pain points related to quality attributes.
- Market and competitive analysis to benchmark capabilities.
- Stakeholder interviews asking about “quality of service” needs.
Requirements should be documented using templates that capture details like:
- Description of requirement
- Measurement benchmarks
- Priority
- Owner
Where possible, quantitative metrics should be defined to assess the fulfillment of the requirement.
Non-functional requirements can be linked to specific user stories and features to show their relevance. However, since they span the entire product, a separate section dedicated to quality attributes is recommended.
Updating this documentation periodically ensures new needs are captured and managed through the product lifecycle.
Validating and Testing Non-Functional Requirements
Thoroughly testing and validating that non-functional requirements have been met is critical before releasing a product. Some techniques include:
- Load testing – Simulating expected usage and pushing performance to identify bottlenecks.
- Stress testing – Overloading the system beyond normal capacity to assess robustness.
- Usability testing – Observing real users interact with the product to evaluate ease of use.
- Security audits – Expert reviews and penetration testing to identify vulnerabilities.
- Compliance testing – Verifying adherence to regulatory standards like HIPAA.
Testing should be conducted early and often, not just before launch. Relevant metrics like speed benchmarks should be tracked before, during, and after testing to quantify results. Tests should cover happy paths and edge cases alike.
Managing and Monitoring Non-Functional Requirements
The work doesn’t end once a product is live. Product managers need to:
- Maintain clear requirement ownership between product, engineering, UX, security teams, etc.
- Set up dashboards and KPIs to monitor the fulfillment of quality attributes long-term.
- Listen to ongoing user feedback to identify new non-functional needs.
- Be ready to re-prioritize requirements as the competitive landscape evolves.
- Advocate for adequate resources to meet non-functional requirements as the product scales.
- Guide trade-off decisions when conflicts emerge between availability, security, performance, etc.
- Update documentation frequently as requirements change based on user input.
Proactively managing non-functional requirements, even after launch, ensures the product continues meeting user and business needs over time.
Best Practices for Product Managers
To effectively oversee non-functional requirements, product managers should:
- Collaborate early with engineering teams to understand technical constraints and trade-offs.
- Conduct user research to elicit needs around quality attributes like usability and performance.
- Create a framework and checklist for capturing non-functional requirements to use consistently across projects.
- Break down vague requirements like “user friendly” into quantifiable metrics and benchmarks.
- Validate non-functional requirements through prototyping and testing with real users.
- Be ready to make tough prioritization trade-off decisions between conflicting attributes.
- Track fulfillment of critical non-functional requirements throughout development.
- Advocate for resources, budget, and time needed to meet quality standards.
- Guide decisions around re-prioritization when business goals or constraints change.
Taking an active role in managing non-functional requirements will help product managers release higher-quality products.
Managing Non-Functional Requirements: Conclusion
In conclusion, properly identifying and managing non-functional requirements is imperative for product managers seeking to deliver excellent products. Non-functional requirements address critical quality attributes that enable products to satisfy user needs and meet business goals. Product managers should make non-functional requirements a priority throughout the product lifecycle, from eliciting, needs early on to validating fulfillment later through rigorous testing.
By collaborating cross-functionally, documenting requirements clearly, and monitoring quality metrics continually, product managers can manage non-functional requirements along with their functional counterparts to release products that go beyond functionality to provide exceptional user experiences.
