Document mapping is typically done during and after the Discovery Sweeps. Until the sweeps are finished you may not know what all the documents are you have. This being the case, it is a dependency.
In a structured system, there are ‘levels’ of documentation. In general terms we have the description of documentation in levels or tiers. As we learned earlier there are typically 4 tiers of documentation in an organization (excluding Ad Hoc documents).
The top tiers normally guide the content and focus of the bottom tiers. In short, each successive lower tier is DEPENDENT upon the upper tier which defines it. This is said to be a ‘Flow Down’ of requirements.
Higher level documents normally cite lower level documents. These citations are important as they form a ‘trail’ which can be followed. The top level documents tend to be general and to some extent vague while the lower level documents provide increasing detail.
Sometimes the reverse also happens - lower level documents cite higher level documents internally. There is controversy as to whether this is ‘good’ practice. In my opinion, requirements should Never flow up.
Document mapping is more important now than ever as mature companies shift towards interdisciplinary (cross-functional) communication and operation. The old way was for departments to ‘pass off’ to another department. The new way causes everyone to be involved. In short, the rise of the importance of Teams requires documentation to be more integrated and consistent - and thus the need for control is greater. This is also the reason for the ‘review’ requirement.