Sales is always a good example.
Here are 6 files that would be used when creating a Purchase Order for a company. Depending on the level of DB normalization, files would contain different information. But, this should give you an idea.
FIle 1 - Customer file -- Contains a unique Customer Number and demographic information about the customer. - Single record per customer.
File 2 - Sales Rep file - Contains a unique identifier about sales personel. Singe record per sales staff.
File 3 - Sales History file -- Contains the unique Customer number. multiple records. Onve for each item purchased. Include date, quantity and PO number.
File 4 - PO file - Contains unique Purchase Order Number -- Conaints date / time of order, date / time shipped, Sales Rep ID#, Total amount, and other fields.Since record per PO.
File 5 - PO detail file - Contains multiple records per PO#. one record with Item #, quanity ordered, quantity shipped, etc.
File 6 - Item file - Contains item informatin - Unique Item number, description, size, cost, and other information that makes theitem unique.