A Data Flow Diagram illustrates the way information flows through a process or system. The information includes data inputs and outputs, data stores, and other sub-processes the data move through. Also known as DFD, Data Flow Diagrams are mainly created to represent the flow of data in a business information system as it depicts logic models and expresses data transformation in a system. The easiest way to understand the flow of data is to create a Data Flow Diagram for an ATM System as it graphically depicts the primary four components of a Data Flow Diagram -- external entity, process, data flow, and data store. A Data Flow Diagram for an ATM System depicts the login request initiated from the user which will get verified from the bank server database. If the provided information is correct then the bank server prompts account information and will accordingly update the database if any request is made by the customer.