Difference: The top-level data flow diagram contains only one process to represent the entire system; the output data flow and input data flow are the input data and output data of the system, indicating the scope of the system and the data exchange relationship with the external environment.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

Data Flow Diagram: DFD for short, it graphically expresses the logical functions of the system from the perspective of data transmission and processing, and graphically depicts the process of data flow and processing in the system. , because it only reflects the logical functions that the system must complete, it is a functional model.

There are no specific physical elements in the data flow diagram, it just depicts the flow and processing of information in the system.

Do not confuse data flow diagram (DFD) with system flow diagram and program flow diagram. Data flow diagram describes a system from the perspective of data, while block diagram describes a system from the perspective of the staff who process the data. to describe the system.

According to the hierarchical data flow diagram, it can be divided into top-level data flow diagram, middle-level data flow diagram and layer 0 data flow diagram. Except for the top-level data flow diagram, other data flow diagrams are numbered from zero.

The top-level data flow diagram contains only one process to represent the entire system; the output data flow and input data flow are the input data and output data of the system, indicating the scope of the system and its relationship with the external environment. Data exchange relationship.

The 0-layer data flow diagram is to refine a certain process in the parent layer data flow diagram. One of its processes can also be refined again to form a sub-diagram. How many levels are there? , generally depends on the complexity of the system.

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