Data Flow Diagram
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Data Flow Diagrams (DFDs)
1
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Specific Instructional Objectives
At the end of this lesson the student will be able to: • • • Identify the activities carried out during the structured analysis phase. Explain what a DFD is. Explain why constructing DFDs are important in arriving at a good software design. • Explain what a data dictionary is. • Explain the importance of data dictionary. • Identify whether a DFD is balanced.
Structured Analysis
Structured analysis is used to carry out the top-down decomposition of a set of high-level functions depicted in the problem description and to represent them graphically. During structured analysis, functional decomposition of the system is achieved. That is, each function that the system performs is analyzed and hierarchically decomposed into more detailed functions. Structured analysis technique is based on the following essential underlying principles: • • • Top-down decomposition approach. Divide and conquer principle. Each function is decomposed independently. Graphical representation of the analysis results using Data Flow Diagrams (DFDs).
Data Flow Diagram (DFD)
The DFD (also known as a bubble chart) is a hierarchical graphical model of a system that shows the different processing activities or functions that the system performs and the data interchange among these functions. Each function is considered as a processing station (or process) that consumes some input data and produces some output data. The system is represented in terms of the input data to the system, various processing carried out on these data, and the output data generated by the system. A DFD model uses a very limited number of primitive symbols [as shown in fig. 5.1(a)] to represent the functions performed by a system and the data flow among these functions.
2
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External Entity
Process
Output
Data Flow
(a)
Data Store
number readnumber validatenumber data-item
Data Flow Diagrams (DFDs)
1
mywbut.com
Specific Instructional Objectives
At the end of this lesson the student will be able to: • • • Identify the activities carried out during the structured analysis phase. Explain what a DFD is. Explain why constructing DFDs are important in arriving at a good software design. • Explain what a data dictionary is. • Explain the importance of data dictionary. • Identify whether a DFD is balanced.
Structured Analysis
Structured analysis is used to carry out the top-down decomposition of a set of high-level functions depicted in the problem description and to represent them graphically. During structured analysis, functional decomposition of the system is achieved. That is, each function that the system performs is analyzed and hierarchically decomposed into more detailed functions. Structured analysis technique is based on the following essential underlying principles: • • • Top-down decomposition approach. Divide and conquer principle. Each function is decomposed independently. Graphical representation of the analysis results using Data Flow Diagrams (DFDs).
Data Flow Diagram (DFD)
The DFD (also known as a bubble chart) is a hierarchical graphical model of a system that shows the different processing activities or functions that the system performs and the data interchange among these functions. Each function is considered as a processing station (or process) that consumes some input data and produces some output data. The system is represented in terms of the input data to the system, various processing carried out on these data, and the output data generated by the system. A DFD model uses a very limited number of primitive symbols [as shown in fig. 5.1(a)] to represent the functions performed by a system and the data flow among these functions.
2
mywbut.com
External Entity
Process
Output
Data Flow
(a)
Data Store
number readnumber validatenumber data-item