Directory contents:

dbmi: DataBase Management Interface (db_*() functions)
  dbmi_base:   contains functions for modules, drivers (../../db/drivers/)
  dbmi_client: contains functions for modules
  dbmi_driver: contains functions for drivers (../../db/drivers/)

sqlp: SQL parser library
stubs: stubs for unimplemented DB functions

The DBMI drivers are stored in 
../../db/drivers/

The DBMI user modules are stored in
../../db/base/

NOTE:
 Please read grass6/db/drivers/README

To generate dbmi_driver/dbstubs.h automatically, run './mk_dbstubs_h.sh' in
dbmi_driver/ directory.