'once you have understood how it should be, which results each procedure should return then coding is the most trivial part.' I wholeheartedly agree with this!

'once you have understood how it should be, which results each procedure should return then coding is the most trivial part.' I wholeheartedly agree with this! The big challenge is that you have the patience (and the patience of the management) to understand the old system thoroughly before starting to write new code.