1. Data Flow Diagram
Zero Level

2. Example 1 Let’s think about video rental system.
New customer can register to the system by providing his/her information.
S/he chooses an item to rent and provides customer ID in order to enter to the system.
Payment can be made over the system. System sends a receipt to the customer. After a while customer returns the item that s/he rented.
When customer registered to the system, system sends a video rental card to the customer.
System also sends monthly and yearly bonus letter to some customers who spend huge amounts for video rent.
Management can take monthly reports from the system.
Accounting department checks total cash received in specific periods.

3. Context Level DFD

4. Zero Level DFD

5. Example 2
Perfect Pizza wants to install a system to record orders for pizza and chicken wings. When regular customers call Perfect Pizza on the phone, their phone number goes to automatically into the Pizza system. The phone number invokes the name, address and the last order date comes automatically up on the screen. Once the order is taken, the total, including tax and delivery, is calculated. Then the order is given to the cook. Areceipt is printed. Occasionally, special offer (coupons) is printed so the customer can get a discount. Drivers who make deliveries give customers a copy of the receipt and coupon (if any). Weekly totals are kept for comparison with last year’s performance. Draw a context level and zero level data flow diagrams for Perfect Pizza.