What's the difference between data stream, system stream, program stream and data stream?

Adhere to multi-DFD, and graphically express the logical function of the system, the logical flow of data in the system and the logical exchange process from the perspective of data transmission and processing. It is the main expression tool of structured system analysis method, and it is a graphic enlargement used to express software model. It describes the transformation of information flow and data from input to output.

Basic elements of a data flow diagram:

2. System flow chart;

Traditional tools for describing the physical model of a system. His basic idea is to describe all components of the system concept in the form of black box with graphic symbols, including programs, files, databases, tables, manual processes and so on. To express the information flow between given components, rather than the control process of processing information.

Illustration:

3. Program flow chart;

4. System structure diagram of the program.

Data flow diagram: the reaction will go with the output, regardless of the time series. It is mainly used for business analysis and detailed design. The directed line segment on the way represents the data flow.

System flow chart: framework of reaction subject.

Program flow chart: program logic describes the control flow in the program, that is, the execution order of each process in the program and the conditions of the execution order. Directed line segments on the way represent the control flow from one process to the next.

System structure diagram of the program: it reflects the calling relationship and hierarchical relationship of modules in the system, and whoever calls has priority relationship. The directed line segment on the way indicates that the control of the program is called from the calling module at the time of calling, and implies that the control will be returned to the calling module at the end of the call.