This Login system DFD depicts how a system processes data in terms of inputs and outputs. As the name suggests, its focus is on the flow of information, where data originates from, where it travels, and how it gets stored. Data flow diagrams became popular in software development in the 1970s. Higher-level DFDs are subdivided into lower-level DFDs, containing more information and functional elements. DFD levels are denoted by 0, 1, 2, and higher. This data flow diagram will primarily see three levels: 0-level DFD, 1-level DFD, and 2-level DFD. This Login system DFD also depicts the entire system as a single bubble with incoming and outgoing arrows indicating input and output data.