Class DB-ENV holds database environment
Class DB-EXT-ENV extended db environment using special buffer readers and writers.
Class DB low level database handle
Class EXT-CURSOR this cursor is generated, when you use db-cursor with an database being type of db-ext
Class DB-STD simple standart database class for databases without transaction support
Class DB-TXN transactional database class
Class DB-EXT when using db-open with an environment of db-ext-env, this will be returned.