The DBI interface allows perl programs to use DBD (Database Definition)
drivers with a common set of routines.  A program can then (theoretically)
change from using mSQL to Oracle (for example) without changing the entire
program around.

This DBI interface is not yet fully specified. The current development
work is focused on writing drivers, such as DBD::Oracle, which also
implement emulations of old perl4 database interfaces, e.g., oraperl.
This strategy enables the DBI and drivers to serve a useful purpose
whilst allowing the real interface to evolve with experience behind the
emulation interface.

WWW: http://forteviot.symbolstone.org/technology/perl/DBI/