Thus far we have discussed the case of characterising relationships between existing
course objects / elements. However, as pointed out in (Brusilovsky, 2003), some types
of adaptation require a model that is different than (although connected to) the main
course model. For example, a model of course concepts and their semantic relations
may need to be maintained “separately” from the model of physical course-material
organisation (e.g., files, navigation hierarchy).