Do you really believe this will help you understand a fairly complex C program ?
Never occurred me to resort to any UML diagram (let alone a database-oriented diagram) to understand how things work in Quake. I just started reading the code. A piece at time. "today, I'll study, let's say... sys_win.c. Yeah, let's learn how Quake actually interfaces with Windows to alloc memory, query the current time and this kind of stuff." . Once I grasped at least the basic idea, I moved to another part. No hurry, one part at time. Helped me a lot, actually. Of course, there are parts that I just never got completely (I mean, why Quake needs several different collision hulls after all ? Can't it make things, you know, just collide directly against the world geometry ?!). But overall is enough to me. Have you already tried this ?
