Softwares-Data Flow Diagram (DFD diagram)

The basis of software requirement analysis: the model analysis method.

The structured analysis method is applicable to the demand analysis of data processing software. It provides the following modeling tools: data flow diagram, data dictionary, machine learning English language, decision table, and decision tree.

 

 

The usage and method of DFD diagram are described here.

 

DFD-Data Flow digraphs

It specifies how data is transformed when it moves in the system, and describes the functions and sub-functions for Data Flow exchange.

DFD graph features.

Abstraction, generalization, and hierarchy.

DFD diagram purpose.

1) system analysts can use this tool to analyze system information processes from top to bottom.

2) You can plot the part to be processed by a computer on the graph.

3) further perform data analysis based on data storage and transition to database design.

4) determine the access method based on the data flow.

5) corresponding to a processing process, the processing method is expressed using the corresponding language, decision table, and other tools.

DFD diagram advantages and disadvantages.

1) The overall concept is strong. Each layer clearly signs "what to do", "what to need", and "what to give"

2) It can reflect the data flow and processing process.

3) as a result of top-down analysis, it is easy to detect logical errors in all parts of the system as early as possible, and it is also easy to correct.

4) it is easy to compare with computer processing.

5) they are not intuitive. Generally, they should be summarized, abstracted, and corrected based on job process analysis.

6) without the help of a computer system, manual plotting would be too troublesome and the workload would be heavy.

Data Flow diagram.

1 sign

2. Name.

1) The name should represent the entire data stream (or storage.

2) do not use empty names without specific meanings.

3) if a data stream name is difficult to start, it may be caused by improper data stream decomposition.

4) The name should reflect the entire processing function, rather than some functions.

5) it is best to add a noun or a ranking group to the name. Avoid "processing" and "processing" as much as possible.

6) data source points and endpoints do not need to be implemented in the system. They represent the external environment of the system. Data sources use names they are used to, such as "Students" and "Administrators ".

Hierarchical Data Flow diagram.

Painting method:

Layer-3 DFD is called the basic system model and can represent the entire software system as an input and outputBlack Box. It is represented by a circle.

Each circle in the previous DFD can be further expanded into an independent data flow chart to reveal the details of the program in the system.

This step-by-step process can continue until the graph at the lowest layer only describes atomic process operations.

Each data flow graph must be balanced and consistent with the data flow graph of the previous layer. Therefore, all input and output flows of the subgraph must match the parent graph.

In summary, this means: from external to inner, from top to bottom, refined layer by layer, and improved refinement.

Determine the system input and output to reflect the system interface on the external environment. Layer-3 DFD expresses the entire system as a processing method. It does not express the data processing requirements and needs to be further refined. Determine and mark the main input and output. Start from the input end and draw a processing frame for data flow according to the business workflow to reflect the actual data processing process and draw the output end gradually, obtain the data flow diagram of the first layer. The processed decibels in the figure are numbered. Refine each processing box. If there is data stream in the processing box, you can divide the processing box into several subprocesses and draw data streams between the subprocessing boxes. A specific process. Repeat the steps until only one simple operation is repeated during all processing, which can be easily implemented by a program.

To express the data processing in the processing process, a hierarchical data flow diagram is required. Based on the hierarchical structure of the system, the hierarchical data flow diagram is used to reflect this structural relationship, so that the entire system can be clearly understood.

The system can be divided into three subsystems: DFD/L1, DFD/L2, and DFD/L3. Layer-2 DFD/1.1 DFD/1.2... and so on.

Eg:

This is the previous figure. First, let's talk about the disadvantages of this graph. First, no data storage files are shown in this figure. Second, there are some problems with the name of the data stream in the figure.

Below is a DFD diagram of the restaurant ordering system I have drawn.

Continue to correct and explore in practice.