Draw a Context as well as Level 0 Data Flow Diagram (DFD) of a ShopSale Management System for a company sailing shops in different parts of country. The Shop Sale Management System works as follows:

Customer Places order. System checks availability of the customer in customer file (If he/she is already a customer). If found, then approved otherwise a new customer is created. Here new customer's info is sent to customer file. Then the availability of products is checked in the inventory file. If found, an invoice is generated. Invoice info is sent to the customer, stock, ledger as well as sales department. If the product is not available at this time, then this info is also sent to the customer.