Thanks for the replies. The mapping I refer to is like this;

source.last_name + source.first_name --> destination file_as_name

this is a simple example of what we are trying to achieve. Problem is we have tons of these and some of the expression logic is fairly complex.

Really just seeing if some sort of tool exists that will document this data transformation logic showing all data flow destination columns and how the source data was transformed for the insert.

Thanks again for the responses.