In Documentum, dm_folder inherits from dm_sysobject, not dm_cabinet. dm_cabinet and dm_folder are siblings in the type hierarchy, both under dm_sysobject.
In Documentum's object model, dm_cabinet is actually defined as a subtype of dm_folder (a cabinet is a special top-level folder), not the reverse, so the statement that dm_folder is a subtype of dm_cabinet is false. This inheritance direction matters for understanding how permissions and behaviors propagate between cabinets and ordinary folders.