An incremental backup copies only datafile blocks that have changed since a specified previous backup. An incremental backups is either a cumulative incremental backup or differential incremental backup.
Although the content of the backups is the same,
BACKUP DATABASE and
BACKUP INCREMENTAL LEVEL 0 DATABASE are different. A full backup is not usable as part of an incremental strategy, whereas a level 0 incremental backup is the basis of an incremental strategy. No RMAN command can change a full backup into a level 0 incremental backup.
As with full backups, RMAN can make incremental backups of an
ARCHIVELOG mode database that is open. If the database is in
NOARCHIVELOG mode, then RMAN can make incremental backups only after a consistent shutdown.