Level 1 Data Flow Diagram for a sales processing system decomposing the main Process Sales function into four sub-processes: Select Products, Calculate Total, Receive Payment, and Update Sales and Inventory Records. Customer interactions flow through product selection querying the Product Database, total calculation, payment receipt, and final record updates to Sales Records and Inventory Records. This DFD clarifies data dependencies and process boundaries, helping stakeholders understand how product availability, pricing, payment, and inventory synchronization integrate in a transactional workflow. Fork and customize this diagram on Diagrams.so to document your own business processes or extend it with additional sub-processes and data stores.