Master

• Large and accessed infrequently
• Stored in a logical way, based around a primary key
• Need to be kept up-to-date

Transaction

• Store the day-to-day data for a company
• Data is stored serially (i.e. chronologically)

Updating the master file

1. The transaction file is sorted in order of primary key
2. For every record in the sorted transaction file, the master file is updated by comparing the new transactions with what is already in the master file
3. New master file produced with any updated data, error reports and printed reports (e.g. invoices)