There tend not to be many resources on this particular topic, as there's no one correct approach and you'll see almost as many ways of structuring the underlying code as you'll see different games -- not to mention plenty of games are quickly thrown together with minimal thought given to structure beyond getting things to work -- even in games that have been beautifully engineered, there may not be any UML (or similar) diagrams for you to investigate.
If it helps though, remember that games aren't all that special -- they're just like any other type of software, and you can apply the lessons you learn from books that aren't focussed specifically on games. If this sort of topic interests you you're probably best of looking for general software design and engineering books rather than references which discuss games.
Sorry my answer isn't more specific, but does that help at all?
Jason Gregory's Game Engine Architecture is, out of my 20 odd game dev books, the only one that has great coverage for this topic - plus it's brilliantly written by a game developer aimed at game developers.