Databasing biological information is a highly complex task and any attempt to provide an easily comprehensible model are bound to fail - at least when attempts are made to inter-connect systems. The present article gives a highly condensed view of the CDEFD model and its embedding in general structures. We opine that biological data in general are covered by this view - in fact, the unit concept already permits extension to many other fields represented in natural history collections. A similar generalization may also be possible for taxonomic and nomenclatural systems used in other fields, e.g. in geology or synthetic chemistry. In this area, as well as concerning ecological categories, more basic research efforts such as the one undertaken by CDEFD are needed.