"pbcoreRelationType describes the relationship between the asset being describe by the pbcore document and any other asset. Ideally it would contain text from a controlled vocabulary for describing relationships. There is some depth to what a relationship could be. The assets can be related as different episodes in a series, different tapes in a box set, or different versions of an original, among others.
Best practice: the assets may be related in that they are different discrete parts of a single intellectual unit, one may be a derivative of another, or they may be different versions that are distinct enough to be described as separate assets."