Part 0 · 1 chapters · ~10 min
What Systems Engineering Is
The discipline from aerospace and operations research, its V-model of decomposition and matching verification, verification versus validation, and how its tools map onto what software teams already do and what they usually miss, introduced through a loan clearance letter service.
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What systems engineering is
reasoning about the whole before building the parts
- The need, stated in plain words.
- System requirements that are testable and measurable.
- An architecture of subsystems and interfaces, traced upward to the requirements.
- Design and build inside the bottom of the V.
- Verification at each level against its counterpart.
- Validation against the need.
| systems engineering tool | what software teams usually call it | what is usually missing |
|---|---|---|
| requirements with traceability | tickets and acceptance criteria | the link from each test back to a requirement, and the implicit requirements |
| interface control documents | API docs, OpenAPI, event schemas | a named owner on each side, and a change process |
| FMEA and fault trees | "what could go wrong" in a design review | doing it systematically, with severity, likelihood and detection scored |
| trade studies | ADRs, RFCs | weighted criteria agreed before the options are scored |
| safety case | a launch checklist | a structured argument, with evidence, that the system is acceptably safe |
| lifecycle and whole-life cost | roadmap, cloud bill | decommissioning, and the cost after launch |
is this waterfall?
No. The V describes what verifies what, not the order work happens in. Agile teams iterate inside each subsystem, and the V keeps the iterations connected to requirements and interfaces that other teams depend on. For a regulated letter that a third party must trust, that connection is the part you cannot leave to chance.
THE V-MODEL
every level of design on the way down has a matching level of verification on the way up
swipe the figure sideways, or tap expand for full screen
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the need
The need: a stakeholder need in plain words. For the running example: "A customer who has fully repaid a loan can get a signed letter confirming they owe nothing, within minutes, that a third party (an employer, an embassy, another lender) can verify."