[Dovecot] Adding new storage backend to Dovecot

I'm exploring adding a new storage backend to dovecot, storing mail in some sort of database, and had a few questions. Hoping someone here might be able to help :)

-Is all of the 'storage' specific code in housed in lib-storage/index? Would adding a new storage backend be as simple as recreating all of the public functions of the current /mbox or /maildir code such as they pertain to that storage mechanism?

-Where is the particular storage method controlled? I've had a look around but can't seem to find where the decision to use the 'mbox' or 'maildir' code is.

-Finally, if there isn't a filesystem associated with the mail storage area, obviously the index data code will need to change somewhere. Any ideas on the complexities of that?

Thanks!