With the caveat of it being a long time since I read the game and not being Shaira, basically every skill was either a root or a branch. Root skills could only be improved up to a certain limit. Once you had reached that ceiling then you had to specialise with a branch skill. So, for example, you might have a root skill called Physics and then branches such as astrophysics, quantum physics and so on. To learn quantum physics, first you had to train its root skill (physics) to maximum then you learned quantum physics. IIRC you start the branch (specialist) skill at a value equal to the root skill.
I've occasionally played with this idea and am currently toying with converting the MRQ style skill set over. E.g. every root skill has a base score equal to two stats and a cap equal to base*3 (or *2) (or a flat max of 90). Once you hit the cap you have to specialise. It's the kind of thing that might be very good for modern and future settings where more complex skill sets fit better than they do in standard fantasy.
