The data flow diagram for a billing system shows how information flows between administrators, users, and vendors. Administrators manage billing and transactions, retrieve and store billing information, and monitor payments. Users can request invoices, view billing information, and register accounts. Vendors provide product pricing and confirm payments and orders. This DFD gives everyone access to accurate and current billing info. It helps make financial transactions smooth. It shows that a good database and clear communication are key for managing billing well.