Lets concentrate on ATC ; it is organized in a five-level hierarchy ranging from anatomical groups to molecules that corresponds to a generalization/specialization classification. It uses an encoding system that can easily be transformed into an explicit OWL concept subsumption hierarchy, e.g., an R5D concept, with an Antitussives label, is created and has the R5 concept, with label Respiratory System as a super concept. This approach, when performed over ATC, yields a concept hierarchy of depth 5 containing over 5000 concepts.