Dfd

Data Flow Diagram (DFD)

DATA FLOW DIAGRAM A DFD has the purpose of clarifying system requirements and identifying major transformation means how data is flowing at various level between source destinations. A DFD consist of a series of bubbles Joint by lines. The bubbles represent data transformation and the lines represent data flow.

The DFD is one of the most important tools to be used by system analyst. The main merit of DFD is that can provide an overview of what files are used, and where the results flow. The graphical representation of the system makes it a good communication tool between a user and an analyst. Symbols used in making data flow diagram are: -

1. Circle or a Bubble:It represents a process that transforms incoming flows into outgoing data flows.

data

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2.

Rectangle: A rectangle represents an external entity, situated outside the system. Entity supplying data are known as sources and those that consume data are called sinks.

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3. An Arrow: An arrow identifies data flow. It also represents data in motion. It is a pipeline through which information flows.

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4. Slant Line: Thin slant line depicts a line. A file or data store stores data. If an arrow points to the file, it indicates operation of writing in the file. If it points away from the file, it indicates operation of reading from the file. If both arrows are there, it indicates that one may write in or read from the file.

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CONTEXT LEVEL DFD

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ER Diagram

E-R DIAGRAM E-R diagram is a physical relationship between different entities. It depicts the overall structure of an organization. E-R Model is a detailed Logical representation of entities. It is an association of data elements for an organization and business area. Basic symbols used for E-R diagram are: 1.

Entity:

It is a thing in real word with an independent existence. An entity may be an object with a physical existence or may be an object with a conceptual existence.

SymbolThere is a type of entity, which is called weak entity:  Weak Entity:

The entity, which has not any key, attributes of their own; these are called weak entity.

2. Attribute: These are properties, which describe an entity.

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Type Of Attributes :  Multivalued attribute: These attributes are shown in double Ovals. It shows the attributes that have multiple values.

 Derived Attribute: These attributes are shown in double dotted lines. Example, Age of the person can be a derived attribute.

Because it is possible to get the age of a person when Date of Birth is known.

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3. Relationship: Whenever an attribute of one entity type refers to another entity type, some relationship exists. It connects entities and represents a meaningful dependency between them.

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4. Primary key:

It is a unique quality and is related with attribute.

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