Flow Diagram DFD

The importance of a streaming diagram (Dfd-data Flow Diagram) makes it important for system analysts to figure out what to do. So how do we draw a streaming chart? What is the difference between a streaming diagram and a system flowchart? Steps
1 What is included in the streaming diagram

The data flow diagram describes the logical model of the system, which does not have any specific physical elements, but depicts the situation in which information flows and processes in the system. Because the flow chart is a graphical representation of a logical system, it is easy to understand even if it is not a professional computer operator.

Do not confuse the streaming diagram (DFD) with the system flowchart and program flowchart. Steps
2 symbols in the streaming diagram

The symbol in the data flow chart is also very simple, only four: 1) external entities; 2) processing; 3) connection; 4) datastore. There are also two of these four symbols. One is Yourdon & Coad method, the other is Gane & Sarson method. It's just a little different. If you use Microsoft Visio, you can only use the Gane & Sarson method.

It is important to note that:

1) processing is not necessarily a program. It can be a system program, a single program or a module of the program, or even a manual processing process;

2) data storage is not equivalent to a file. It can be a file, a part of a file, a database element, or a part of a record; it represents a static data.

3) Data flow is also data, is Dynamic data. Steps
3 separating elements in a streaming diagram

Suppose a factory's purchasing department needs a daily order statement. The report is sorted by part number, and the table lists all the parts that need to be ordered again. For each part that needs to be re-order, the following data should be listed: Part number, part name, order quantity, current price, main supplier, secondary supplier. Part warehousing or attendance is called a transaction, and the transaction is reported to a given system by a CRT terminal placed in the warehouse. When the inventory quantity of a part is less than the inventory critical value, it should be re-orders.

SOURCE Point/End point (External entity)	Buyer Warehouse Manager
Data processing	Generating Report Processing transactions
Data flow	Orders Report Part number Part name Order Quantity Current price Major suppliers Secondary vendor transactions Part number Transaction type Number
Data storage	Order information (see Order Report) inventory List Part number Library stock Critical value of library stock

Steps
4 gradually decompose to draw a flow chart

The first step is to draw the most generalized system model. Because any system essentially consists of several data source points/endpoints and a processing component. This processing represents the basic function of the system to transform the data processing.

Refinement of the above image

A little more refinement.

Sketch out the border

Finally refine

Steps
5 named methods

1) name the data stream (or data store)
A The name should represent the content of the entire data stream (or data store);
B Do not use empty, less specific names (such as "data", "input");
C If it is difficult to name a data stream (or data storage), it is probably because of the decomposition of the flow diagram is not properly caused, should try to re-decomposition flow chart;

2) for processing naming
A The data flow is usually named first, and then the processing associated with it is named;
B The name should reflect the entire processing function;
C Should try to avoid the empty general verb to do the name, such as "Processing", "processing";
D Usually named after a verb, if it is necessary to use two verbs to describe the function of the whole processing, it may be necessary to decompose the processing into two processing more appropriately;
E. If you are having difficulty naming a process, it is likely that you have found an improper decomposition and should consider re-factoring.

3) Name the data source/end point
Typically, when naming data source points/endpoints, use the names they are accustomed to in the problem domain (such as "Warehouse Administrator", "buyer").

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