I hope I understand your question correctly. From what I find documents are mostly in a table, and hierarchy is provided by another one, like a `categories` ta

I hope I understand your question correctly. From what I find documents are mostly in a table, and hierarchy is provided by another one, like a `categories` table, in which a `parent_id` column is used to refer to itself and form a tree. It helps a lot to cache that tree, as it usually is often used, not too big, rarely changes, and needs more then one query (mostly). In Postgress there is the `ltree` extension, but then the solution is Pg specific.