Traceability (Bi-Directional)
Section 08: Software Certification (DO-178C)
Definition
The ability to trace relationships between lifecycle data items in both forward (from requirements to implementation and test) and backward (from implementation and test back to requirements) directions. DO-178C requires bi-directional traceability at multiple levels: (1) System requirements to HLRs and HLRs back to system requirements; (2) HLRs to LLRs and LLRs back to HLRs; (3) LLRs to source code and source code back to LLRs; (4) HLRs to test cases/procedures and test cases/procedures back to HLRs; (5) LLRs to test cases/procedures (for applicable levels) and test cases/procedures back to LLRs. Forward traceability ensures that all requirements are implemented and tested. Backward traceability ensures that all code and tests can be justified by a requirement (detecting extraneous code and unnecessary tests).
Where This Shows Up
Bi-directional traceability is one of the most labor-intensive but fundamental aspects of DO-178C compliance. It provides the objective evidence that the software implements all its requirements and only its requirements, and that all requirements are verified. Traceability gaps, requirements without corresponding code or tests, code without corresponding requirements, are common audit findings and indicate potential deficiencies in the development or verification process.
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Primary Sources
Defines traceability objectives for the software verification process, including bi-directional traceability requirements at each software level.
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