2. DFD
• Software design involves activities, in which transformation of
Requirement specification into abstract view of system is one of them.
• A Data Flow Diagram (DFD) is a graphical representation of the "flow" of
data through an information system.
• DFDs are also used to represent How data is Processed.
• DFD Shows
• Input Data to the system
• Output Data from the system
• Where data is stored
• DFD does not shows
• Timings of data process operations
• Sequence or parallel operations of data process
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3. Elements of Data Flow Diagrams
• Process – functions of a system to transform input data into output
data. (How data is processed)
• Represented by “circle”.
[name]
Process
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4. Elements of Data Flow Diagrams
• Data Store – Where data is stored. E.g Files, Database.
[Name]
Data Store
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5. Elements of Data Flow Diagrams
• Entity – source and destination of data to/from the system.
• Represented by “Rectangle”
• Source – Entity that supplies data to the system.
• Sink – Entity that receives data from the system.
[name]
Entity
Source Sink
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6. Elements of Data Flow Diagrams
• Data Flow – represent data flow along with direction of flow
(source/sink).
[Name]
Data Flow
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7. Types of DFD
• Physical DFD
• Graphical representation of the system showing system’s internal and
external entities and flow of data in and out of these entities
• Describes entities involved in the system
• Does not describe how processes are performed in the system
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8. Types of DFD
• Logical DFD
• Describes System and how processes are performed on data in the system
• Logical DFD represents system’s activities where are Physical DFD represents
system’s structure.
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9. Levels of DFD
• Level 0
• Highest abstraction level DFD.
• All components within the system boundary are included within a DFD
• External entities lie outside the system boundary.
• The data flow arrows to and from the external entities will indicate the
system’s relationship with its environment
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