The Top Down approach starts with the Design Requirements and then decide on the intermediate and final steps to get the design implemented.
The approach is used some software projects.
It may also be used in the writing of a book. One first decides on the structure and contents.
The Bottom Up approach It may also be used in the writing of a book. is used when one has a set of bases, foundations and libraries. The building blocks are then assembled and refined to develop a desired product.
The approach is used to develop several software.
It may also be used in the writing of a book. If one has written posts for a long time, they may be used as a basis for further development into an e-book or printed book.
The Middle Out approach up uses a hybrid (part Top Down and part Bottom Up). It is important to make sure that the two parts meet properly.
In the context of publishing, a group of writers and editors can come up with a Design for the book, use existing material as much as possible and try to bridge the gap with new material.