What Are Data Flow Diagrams
A data flow diagram (DFD) is a significant modeling technique for analyzing and constructing information processes. DFD literally means an illustration that explains the course or movement of information in a process. DFD illustrates this flow of information in a process based on the inputs and outputs. A DFD can be referred to as a Process Model.
Additionally, a DFD can be utilized to visualize data processing or a structured design. A DFD illustrates technical or business processes with the help of the external data stored, the data flowing from a process to another, and the results.
A designer usually draws a context-level DFD showing the relationship between the entities inside and outside of a system as one single step. This basic DFD can be then disintegrated to a lower level diagram demonstrating smaller steps exhibiting details of the system that is being modelled. Numerous levels may be required to explain a complicated system. Therefore, the principle for creating a DFD is that one system may be disintegrated into subsystems, which in turn can be disintegrated into subsystems at a much lower level, and so on and so forth.
Every subsystem in a DFD represents a process. In this process or activity the input data is processed. Processes cannot be decomposed after reaching a certain lower level. Each process in a DFD characterises an entire system.
In a DFD system, data is introduced into the system from the external environment. Once entered the data flows between processes. And then the processed data is produced as an output or a result.
Flow diagrams in general are usually designed using simple symbols such as a rectangle, an oval or a circle depicting a processes, data stored or an external entity, and arrows are generally used to depict the data flow from one step to another. A DFD usually comprises of four components. These four components can be represented by four simple symbols. These symbols can be explained in detail as follows: External entities (source/destination of data) are represented by squares; Processes (input-processing-output) are represented by rectangles with rounded corners; Data Flows (physical or electronic data) are represented by arrows; and finally, Data Stores (physical or electronic like XML files) are represented by open-ended rectangles. DFDs can be created using different methodologies or notations such as Structured Systems Analysis and Design Method (SSADM), Yourdon/DeMarco, Metrica and Gane & Sarson methodologies. DFDs can be automated with minimal effort using software such as SmartDraw, ConceptDraw, EDraw, EDGE Diagrammer, Patton & Patton Software and many more.
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