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A Data Flow Diagram (DFD) is a traditional visual representation of the information flows within a system. A neat and clear DFD can depict the right amount of the system requirement graphically. It can be manual, automated, or a combination of both.
It shows how data enters and leaves the system, what changes the information, and where data is stored.
The objective of a DFD is to show the scope and boundaries of a system as a whole. It may be used as a communication tool between a system analyst and any person who plays a part in the order that acts as a starting point for redesigning a system. The DFD is also called as a data flow graph or bubble chart.

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    DFD komponentlarini sanab bering.
    

Components of Data Flow Diagram:
Following are the components of the data flow diagram that are used to represent source, destination, storage and flow of data.
Entities:
Entities include source and destination of the data. Entities are represented by rectangle with their corresponding names.
Process:
The tasks performed on the data is known as process. Process is represented by circle. Somewhere round edge rectangles are also used to represent process.
Data Storage:
Data storage includes the database of the system. It is represented by rectangle with both smaller sides missing or in other words within two parallel lines.
Data Flow:
The movement of data in the system is known as data flow. It is represented with the help of arrow. The tail of the arrow is source and the head of the arrow is destination.

67. 
    DFD darajalarini aytib bering.
    

1. Context diagram: A context diagram provides an overview of the system's interaction with the entities of the organization. That and seeing a high-level view of its environment. , which gives the boundary of the discontinuity and the termination point of the discontinuity.
2. Level 1 Diagram: Level 1 data flow diagram is a graphical representation of the arrangement of data in a single process of the system. It describes the inputs, processes, and how to identify system problems.
3. Level 2 Diagram: Level 2 data flow diagram takes the Level 1 diagram and goes deeper into the systems of the system processes. This provides a complete overview of the data view for a particular process. It shows various components involved in processes such as objects, data storage and transformation.
4. Level 3 Diagram: Level 3 data information diagram provides the smallest view of system processes and data acquisition. This document shows how each process is connected and how data is transferred between each one. The job is to help identify areas of potential improvement or points of failure in the system

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