Each database instance has a unique database ID.
The database system writes the database ID to the following locations:
· The restart record in the data area ® identifies the database instances data
· The information page of the log area ® identifies the database instances log entries
· The information page of each backup ® identifies the database instances backups
If you restart or restore the database instance, the database system uses the database ID to check if the log entries and backups that are to be used really belong to this database instance.