Rodney has just begun to provide gas to a limited number of customers. It is expected that the numberof customers will increase as further gas pipes areinstalled. Currently the billing is done manually, but itis planned to computerise the system in anticipation of increased volumes of users. You have been requested to investigate the system and prepare a system proposal. This is what you have found out from your information gathering;

The meter reader visits the gas customers every six weeks in order to read their gas meter. When all readings have been logged for the period, the meter reader brings the log into head office wherethe accounts clerk copies the readings into a Customer Gas Meter Readings file which contains, for each customer, details of their previous readings.

To produce the bills for the customers, theaccounts clerk subtracts the customers previous meter reading from their current reading, in order to find the total vol- ume of gas used for theperiod. This is multiplied by the gas charge ratewhich the clerk finds in a Gas Charge Rates file. If this is the first bill for the customer, acharge for installation may be added, and sometimes there are maintenance charges. These extra charges are supplied by the Maintenance Department. The gas charge rates are set annuallyby management. All charge amounts are added toany previous amounts owed which are found forthe customer in the Outstanding Bills file. The current bill is posted to the customer.

Customers post their payments to the Rodney offices. The payments are banked and a List of Deposits is returned by the bank. This list is compared to the Outstanding Bills and paid bills are placed in the Paid Invoices file. Partial payments are recorded on the matching bill which remains in the Outstanding Bills file.

Please provide a Context Diagram.

Please provide a Top Level Dataflow Diagram.