Online Data Flow Diagram (DFD) Creation Tool

External Entity: Represented by a rectangle, it represents people or things outside the system that exchange information with the system.
Data Store: Represented by two parallel lines, used to store data, such as databases, files, etc.
Processing Process: Represented by a rounded rectangle, it processes input data to produce output data.
Data Flow: Directed arrows connecting various elements, indicating the direction of data flow.

In the system analysis and design phase, data flow diagrams visualize the data flow and processing processes within the system, helping analysts fully understand user business, while clearly showing the interaction relationships and interface design between modules.
In the system maintenance and optimization phase, data flow diagrams can help maintenance personnel quickly locate the problem, analyze the impact of the problem on the entire system.
In the cross-department communication and collaboration phase, data flow diagrams, as a general graphical tool, can promote a common understanding of the system by personnel from different departments, reducing misunderstandings.

Top-Level Data Flow Diagram: Represents the relationship between the entire system and external entities, but does not delve into the internal workings of the system.
Level 0 Data Flow Diagram: Breaks down and refines the basic system model to form a Level 0 data flow diagram.
Intermediate-Level Data Flow Diagram: Further refines the system functions in the higher-level data flow diagram, the number of intermediate levels generally depends on the complexity of the system.
Bottom-Level Data Flow Diagram: The most basic processing process that cannot be further decomposed.

Thoroughly understand user needs and business processes, design closely around the system's goals;
Use a top-down, stepwise refinement approach to design data flow diagrams, ensuring consistency between data flow diagrams at different levels during the decomposition process;
Ensure matching of input and output data volumes, maintaining balance in data volumes before and after processing;
Correctly use standard symbols and follow naming conventions.

A context diagram, also known as a top-level data flow diagram, is the starting point for system analysis. It depicts the overall system in a highly abstract manner, viewing the entire system as a single processing process (usually represented by a circle or rectangle), only showing data input and output between the system and external entities (such as users, other systems, etc.), without involving specific processing details within the system, providing a framework and boundary for subsequent detailed analysis.