At a lower level than De Bra, we also need to be able to define “assets” associated with “learning objects / elements” which can have standardised relationships to each other and to the enclosing object. Consider, for example, two mutually exclusive elaborations of a given concept, one being brief and the other detailed; contrast that with two complementary elaborations of a given concept, the first being a required brief reading, while the second being an auxiliary amendment to the first.