@ cheten. Thanks. (I presume you meant to say "adapter" in that last sentence, but had a little slip). Yes, I reckon that's right. These are pre-existing interfaces, not subsystems (I don't think).
Presumably to qualify as a "subsystem" it would have to be within your own app (rather than from outside)? Not so sure about that one.
@ vampyre. Yes, we did give it quite a good go, eh? No harm done, then. Theoretically it's my last, too, but I'm not doing it again. If I can't pull off this exam, that's it. Hello INF. (I'm also chipping away at more maths modules - with plans to torture myself with 5 next semester if possible, but have no real idea what I'd do with those in practical terms yet.)
Edit. Yes I found out about the assistance offered sort of half way. I suppose I should've joined in then, but I'd already decided it's almost a hopeless cause, regardless. I mean whatever happens now, there's that fail against my name from back then, isn't there? It's not as if it's possible to repair that kind of damage.