Separate Constructing a System from Using It

First, consider that construction is a very different process from use. As I write this, there is a new hotel under construction that I see out my window in Chicago. Today it is a bare concrete box with a construction crane and elevator bolted to the outside. The busy people there all wear hard hats and work clothes. In a year or so the hotel will be finished. The crane and elevator will be gone. The building will be clean, encased in glass window walls and attractive paint. The people working and staying there will look a lot different too.

Software systems should separate the startup process, when the application objects are constructed and the dependencies are “wired” together, from the runtime logic that takes over after startup.