When data is backed up, the database parameters are backed up too. Before data is restored, a check is run first to see if the database parameters from the data backup are compatible with the current database parameters of the target database instance.
Example
A UNICODE database instance backup is not allowed in a non-UNICODE database instance.
The DB parameters of the target database must match the DB parameters saved in the data backup. At present, this only affects the special database parameter _UNICODE.