FDR (Failure Divergence Refinement)

Failure Divergence Refinement (FDR) is a formal method used in system design to verify that an implementation aligns with its specifications. It involves systematically checking whether every possible behavior (including failures) of the detailed design is consistent with, or refined by, the specified behavior. In essence, FDR ensures that the actual system implementation does not introduce unexpected behaviors or failures beyond those allowed by the specification. This process provides confidence that the system’s design correctly satisfies requirements, especially important in safety-critical systems like aerospace or medical devices.