DEFINE_DB_SERVER can be used in isolation from the other BIFs to just override the connection parameters and database type or it can be used with the full set of related BIFs in this sequence:
DEFINE_DB_SERVER, CONNECT_SERVER, CONNECT_FILE.
The full set of BIFS is only needed when the OTHER File is in a database with a different DSN to the one with which it was loaded.
To connect to all the default databases on startup, that is all the databases defined in the OAMs, it is necessary to DEFINE_DB_SERVER and CONNECT_SERVER for each database using the DSN that is in each OAM. CONNECT_FILE is not required if the DSN is the same as in the OAM. That is, an OTHER File is implicitly connected to the database from which it was loaded.
If your environment has a development, test and production version strategy, the simplest way of managing the differing locations of Other Files as the application passes through the various stages, is to use the same ODBC DSN but alter the definition of it to point to a different physical database. Thus, the default database embedded in the OAM will access a different physical database.