Comment by secthrowaway

Yeah, that model is more or less what's in use. Except the real-world version is a bit more complicated and messier (and more confusing). But the principle is all the same. Read goes down, write goes up.

You can move information down only if the information is at the level you are moving it to and it's been properly signed off.

e.g. something that is marked Secret, but written to a Top Secret system, can be moved back down to the Secret system)