A Payroll system is usually run as a batch processing system. Data may be entered for a number of departments or branches of a company and then the processing is done when all the data has been collected.
As there is no urgency for the output, the payroll processing may be run at off-peak times (e.g. overnight).
The database of the employees and the timesheets will need to be kept secure from unauthorised access - employees must not be able to alter their data!
The employee database is updated in the payroll process. A backup copy of the database is made before this is done.
The new database is called the son and the backup is the father. Previous generations of backups are referred to as grandfather, etc.