When defining large number of document types, it saves lot of work to group common types in groups to inherit common attributes etc. This is limited by the current way of defining reference document. The reference documents has to be defined as a subtype of reference document type.
A more flexible solution shall be to define reference/describe link as a attribute or setting for each document type in type manager. In this way, describing and reference documents can be grouped in a logical way, and not depending of link type.