Hierarchical diagnostics requires that the diagnostic reasoner be able to correlate status information from different levels of the design hierarchy. For example, if a system (top-level) capability is not behaving correctly, a hierarchical diagnostic reasoner will begin by calling into suspicion the various system-level functions that contribute to that behavior. Diagnostics may then use Built-In-Test (BIT) results from lower-level components to rule out many of the lower-level "child" functions that collectively produce those upper-level system functions. As an upper-level function's lower-level "children" are proven good, the diagnostics adjusts the relatively likelihood of that function's having failed.
The eXpress diagnostic engine supports the following hierarchical inferences:
When an output function is proven good, then all lower-level child functions and failure modes are inferred to be good.
A function is inferred to be good when all lower-level child functions/failure modes have been proven good.
If a function is called into suspicion, then all unproven lower-level child functions and failure modes are also called into suspicion.
If a function or failure mode is called into suspicion, then all upper-level parent functions are also called into suspicion.
