Data flow diagram (DFD for short) is a major tool that can comprehensively describe the logical model of an information system. In short, it describes the movement and transformation process of data flow and processing in the system process in a graphical way, reflecting the flow direction of data, natural logical process and necessary logical data storage. After reading this definition, it still seems difficult to clarify. Don’t be confused, this article will introduce you to the meaning and examples of graphic symbols used in data flow diagrams in detail.

Basic symbols of data flow diagrams

Data flow diagrams usually use four basic graphical symbols: external entities; processing procedures; data flow; data storage (see the figure below).

Symbol meaning of data flow chart

1. External entity (Entity): refers to people or things outside the system and related to the system. It explains the external source and destination of the data. Usually external entities are represented by square boxes in the data flow diagram, with the name of the external entity written in the box. If you want to distinguish between multiple different external entities, you can label each entity with a lowercase letter.

2. Process: refers to the logical processing of data, used to change data values. Processes are represented by ovals in data flow diagrams.

3. Data Flow: refers to the input or output of the processing function. It is represented by a horizontal, curved or vertical connecting line, and an arrow indicates the direction of flow. You can indicate the data flow name next to the arrow.

4. Data Store: Represents the place where data is saved, and it is used to store data. It is represented by an open narrow rectangle. You can write the data storage name inside the rectangle. For the convenience of distinction and reference, add a small box at the left end and mark it with a logo consisting of the letters D, M, T and numbers.

"D" — refers to a permanent computer file.

"M" - refers to a manual file.

"T" - refers to a temporary storage that will be deleted after processing.

Examples of using data flow chart symbols

Once you understand these flow chart symbols, you can try your hand at drawing data flow charts. By the way, a usage example of data flow diagram symbols is attached for your reference. For more flowchart illustrations, please visit Flowchart Templates .