Software engineering is about how we organize and structure larger programs, so they are easier to maintain, modify, and evolve. Chapter 15 covers functional programming and how it helps create more maintainable software and encourages new perspectives on how to think about code.
Chapter 16 focuses on the physical organization of software into modules, directories, and files, tying this in with dependency management. Large software is most often composed of many packages made by different teams. This part focuses on developing a solid system to handle versioning of software packages that depend on each other.