In really big system, there is always something that will go wrong. And it’s not possible to master all the different scenario that will arise. The file is delivered a little bit later, a mapping is not started every day, a new process is added, the file system gives a bad block and I don’t talk about the network… In other words, that’s life. One of the answer of this kind of situation, is to embrace this fact of life and to make every mapping recoverable / restartable (ie with little or no dependency). The visualization of dependencies is generally made through what it’s called a death star. Not easy to do but really nice to have.