One way to achieve this is to restrict the number of processes in a data-flow diagram.For example, there can be only one entity CUSTOMER in all levels of the data-flow diagrams or here can be only one process named CALCULATE OVERTIME among all levels of data-flow diagrams.Use unique names within each set of symbols.The context level diagram gets the number 0 (level zero).For example, Grading System, Order Processing System, Registration System.The process name in the context diagram should be the name of the information system.The context diagram must fit in one page.For example, level n & n+1 must have the same inputs and outputs Guideline for Developing Data-Flow Diagram Context Diagram - Level 0 When performing top-down decomposition to a DFD to lower level DFDs, the inputs and outputs must be conserved between levels of DFDs. As shown in the Figure, DFD Leveling is first displaying the targeted system as a single process, and then showing more detail until all processes are functional primitives. Leveling is done by drawing a series of increasingly detailed diagrams until the desired degree of detail is reached. Top-down decomposition, also called leveling, is a technique used to show more detail in lower-level DFDs.
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