Manual Testing Question:

Bidirectional traceability needs to be implemented both forward and backward (i.e., from requirements to end products and from end product back to requirements).
When the requirements are managed well, traceability can be established from the source requirement to its lower level requirements and from the lower level requirements back to their source. Such bidirectional traceability helps determine that all source requirements have been completely addressed and that all lower level requirements can be traced to a valid source.