The tree is close to the DocBook Model.
BOOK is the root component in the database so there is one root for each language version.
There are database-based rules for deciding the component types which a component of a particular type may add as children. Each component has a Common Component ID which points back to the identifier of the corresponding component in the English language version. All data are stored as Unicode. Version control is included within the structure. The DocBook DTDs are reasonably close to our needs.