4. 3 DATA FLOW DIAGRAM A data flow diagram is a graphical technique that depicts information flow and transforms that are applied as data move from input to output. The DFD is also known as Data Flow Graph or Bubble Chart. The DFD is used to represent increasing information flow and functional details. Also DFD can be stated as the starting point of the design phase that functionally decomposes the requirements specifications down to the lowest level of detail.
A Level 0 also called a fundamental system model or a context level DFD that represent the entire software elements as a single bubble with input and output data indicated by incoming and outgoing arrows, respectively. Additional process and information flow parts are represented in the next level, i. e. , level 1 DFD. Each of the processes represented at level 1 are sub functions of overall system depicted in the context model. Any processes that are complex in level 1 will be further represented into sub functions in the next level, i. e. , level 2.
Data flow diagram is a means of representing a system at any level of detail with a graphic network of symbols showing data flows, data stores, data processes and data sources. The purpose of data flow diagram is to provide a semantic bridge between users and system developers. The diagram is the basis of structured system analysis. A DFD describes what data flows rather than how they are processed, so it does not depend on hardware, software, data structure or file organization. 4. 3. 1 Components of Data Flow Diagram There are four symbols that are used in the drawing of Data Flow Diagrams: Entities External entities represent the sources of data that enter the system or the recipients of data that leave the system. * Process Processes represent activities in which data is manipulated by being stored or retrieved or transformed in some way. A circle represents it. The process will show the data transformation or change. * Databases Databases represent storage of data within the system. * Data Flow A data flow shows the flow of information from its source to its destination. A line represents a data flow, with arrowheads showing the direction of flow.