EN 50716:2023 - Railway Applications - Requirements for Software Development 7.4: Component design

Aim: a component design that achieves the Software Design Specification, and a component test specification that achieves the component design, both to the extent the integrity level requires (Tables A.1 and A.20). The Designer writes a Software Component Design Specification per component; for each component the author, a short description and a configuration history are held, the history identifying every current and earlier version with its date, author and what changed. The specification identifies every lowest-level unit (subroutine, method, procedure) traced to the level above, their detailed interfaces with inputs and outputs to the environment and other components, their integrity level (not split further inside the component), and detailed algorithms and data structures; it is self-consistent, can be turned directly into code, is readable, understandable and testable, keeps component size and complexity balanced, and uses Table A.4 techniques as the quality plan chose. The Tester writes a component test specification per component that meets the generic test specification rules, defines and justifies the coverage criteria and target (Tables A.5 and A.21), and designs tests to confirm the intended functions, check how internal parts interact to deliver them and exercise every part of the component, using Table A.5 techniques as the verification plan chose. The Verifier's component design verification report checks the design against the design specification, its readability, traceability and content, the test specification as a test set and its own content, and the decomposition for achievable performance, testability and maintainability.