What Is a Data Flow Diagram?

Data Flow Diagram (DFD / Data Flow Chart) is a main tool that can comprehensively describe the data flow of the system. It uses a set of symbols to describe the overall picture of the information in the entire system and comprehensively reflects the information in the system. Flow, handling, and storage in the environment.

Data flow chart

Data Flow Diagram (DFD / Data Flow Chart) is a main tool that can comprehensively describe the data flow of the system. It uses a set of symbols to describe the overall picture of the information in the entire system and comprehensively reflects the information in the system. Flow, handling, and storage in the environment.

Data flow diagrams have two characteristics: abstraction and generality. Abstraction means that the data flow diagram removes specific organizations, workplaces, and material flows, leaving only information and data storage, flow, use, and processing. Generality means that the data flow diagram links the system's processing of various services and considers it to form a whole.

Chinese name

Data flow chart

Foreign name

Data Flow Diagram, DFD / Data Flow Chart

Description

Tools for system data flow

Draw

Data Independent Abstraction

the way

Graphic mode

Make use of

symbol

In order to describe the information flow and processing of complex software systems, hierarchical DFD can be used to describe. Hierarchical DFD has top, middle, and bottom layers.

(1) The top layer. Determine the scope of the system, determine the input and output data streams, it describes the boundaries of the system, and abstracts the functions of the entire system into one process. There is only one top-level DFD.

(2) The middle layer. Below the top layer are several intermediate layers. An intermediate layer is both the decomposition result of the processing on the previous layer and an abstraction of the processing on the next layer, that is, it can be further decomposed.

(3) The bottom layer. If the processing of a DFD cannot be further decomposed, this DFD is the bottom layer. The processing of the underlying DFD is made up of basic processing. The so-called basic processing refers to processing that can no longer be decomposed.

The basic components of a data flow diagram

System components include the system's external entities, processing processes, data storage, and data flow in the system.

1, external entities

An external entity refers to a person or thing outside the system that is connected to the system. It describes the external sources and destinations of data, and belongs to the system's external and system interfaces. External entities that support system data entry are called source points and support the system

Data flow chart flowchart making principle

All graphic symbols on the data flow chart must be the four basic elements described above.

The main diagram of the data flow chart must contain the four basic elements described above, all of which are indispensable.

The data flow on the data flow chart must be enclosed between external entities. There can be one or more external entities.

The processing process has at least one input data stream and one output data stream.

Any data flow subgraph must correspond to a processing process on its parent graph. The input data flow and output data flow of the two must be consistent, which is the so-called "balance".

Each element on the data flow chart must have a name.

Data flow chart flowchart making steps

Treat a system as a whole function, and clarify the input and output of information.

Find the external entities of the system. Once an external entity is found, the interface between the system and the outside world can be determined, and the source and destination of the system's data flow are found.

Find the input data flow and output data flow of the external entity.

Draw the external entities of the system on the edge of the diagram.

Starting from the input stream (source) of the external entity, according to the logical requirements of the system, a series of logical processing processes are gradually drawn until the output stream required by the external entity for processing is found, forming a closed data stream.

The internal data processing of the system is regarded as an overall function, and the information processing, transmission, and storage processes are also internal.

Analyze this level by level until all processing steps are specific.

Notes on data flow chart production

About the division of levels

Expanding the data flow chart layer by layer is to decompose some processing boxes in the previous layer. With the decomposition of processing, functions become more and more specific, and data storage and data flow become more and more. There is no absolute standard for how to divide the levels and to what extent. Generally, it is considered that the expanded level is consistent with the management level. It can also be divided more finely. The decomposition of processing blocks should be natural. Pay attention to the functional integrity. It is advisable to decompose it into 4 to 10 processing frames.

Check data flow chart

The understanding of a system cannot be perfect from the beginning. When we begin to analyze a system, although we have incorrect and inaccurate understanding of the problem, it should still be expressed in a data flow chart based on our understanding. Check it out and modify it gradually to get a perfect drawing.

Improve the comprehensibility of data flow chart

Data flow diagrams are a tool for system analysts to investigate business processes and exchange ideas with users. Therefore, the data flow diagram should be concise and easy to understand. This is also conducive to the subsequent design and maintenance of the system manual.