look into the help about parent/children relations. Use master references to asssembly, like datum planes, axis, points, coor sys from the assembly (or any other that does not belong to any component, but to the assembly per se). Other that surfaces of featyres from the parent component. If you assembly a component to another (mates, align, insert, tangent, etc), that component will depend and require the previous component to determine its posittion at all time. Look up this information better in pro/e help tool