I define reliability as the degree to which a system performs specified functions under specified conditions for a specified period of time. Therefore, I treat it as a measurable non-functional expectation. First, I state the function, the operating conditions, and the time span. Next, I add objective metrics such as availability, failure rate, MTBF, or mean time to repair. Moreover, I describe the operational environment. Consequently, teams can test and verify the statement.
Traceability links this expectation to stakeholders, design items, and test cases. For example, I connect each statement to a unique ID, the key design decisions, and concrete test procedures. Furthermore, I record who changed it and when. Thus, I support auditability and compliance. In addition, this approach aligns with common guidance on identification and traceability. Similarly, ISO/IEC 12207 and ISO/IEC 15288 address requirements analysis and management, while IEC 61508 emphasizes functional safety and traceability. Notably, IEC 61508 defines Safety Integrity Levels (SIL 1 to SIL 4), where higher SIL implies stricter dependability targets. Therefore, I map such statements to applicable standards and safety levels when needed.
To measure outcomes, I apply the Goal–Question–Metric (GQM) method. First, I define the goal, such as dependable delivery for a release. Next, I ask questions like: when will the release go live, and how likely is on-time delivery? Then, I select metrics. For example, I use earned value analysis to estimate deadlines. In addition, I monitor defect rates, regression failures, and uptime. Consequently, I produce focused reports that match stakeholder information needs.
I run risk analysis for every significant change. Therefore, I assess how the change affects dependability targets. I also perform critical path analysis on requirements-engineering activities to identify tasks that can delay the final deadline. Then, I allocate resources accordingly. For example, I schedule regular risk workshops and keep security experts available. Thus, I reduce avoidable delays and protect the agreed targets.
I write these statements in clear, testable terms. For example, I state: “The system shall achieve 99.95% availability during business hours over one year under a 95th-percentile load profile.” In addition, I define acceptance criteria and test methods, including monitoring tools, test data, and simulation scenarios. Consequently, verification and validation teams can prove compliance.
I keep links to safety cases and change records. Moreover, I document assumptions and operational limits, such as environmental constraints, maintenance windows, and redundancy strategies. Finally, I monitor field data and perform growth analysis over time. Then, I update tests and statements based on real-world performance.
Overall, I treat reliability as a living expectation. Therefore, I measure it, trace it, and manage changes continuously. Furthermore, I align it with relevant standards, safety levels, and reporting needs. Consequently, teams build dependable systems that meet stakeholder expectations.