Erd Lecture 1

Design Tools

Picture is worth a thousand Words

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To be covered…

DATA FLOW DIAGRAM

Context Diagram

Diagram 0

Detailed DFD

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What are Data Flow Diagrams?

Data flow diagrams illustrate

how data is processed by a

system in terms of inputs and

outputs.

i.e. They show flow of data

through the organization

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Purpose/Objective

The purpose of data flow diagrams is to provide a

bridge between users and systems developers.

The diagram Features are:

Graphical: Eliminating need of thousands of words.

Logical Representations: Modeling WHAT a system

does, rather than physical model showing HOW it does

it.

Hierarchical: Showing systems at any level of detail.

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Data flow diagrams have the

objective of avoiding the cost of

User/developer

misunderstanding

a system.

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Description

Data Flow Diagrams

are composed of the

four basic symbols.

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Description

The External Entity

symbol represents

sources of data to the

system, or destinations

of data from the

system.

i.e. A Person, A System, or

an organization that sends

or receives data

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Description

contd..

The Data Flow

symbol represents

movement of data.

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Description

contd..

The Data Store

symbol represents

data that is saved on

some file or in a

table.

Student File,

Faculty File,

Result File.

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Description

contd..

The Process symbol

represents an activity

that transforms or

manipulates the data

(A process transforms

incoming data flow

into outgoing data

flow).

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Constructing a DFD

Start with Context diagram which shows only a single

process (represents the entire system), and external

entities

Identify the functions to be performed

Show the information flow between functions and

identify data stores and external entities

Repeatedly elaborate on the DFD ( bottom up and

top down )

After each elaboration is complete validate the DFD:

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Identify missing functions

Identify functions that need more detail

Rearrange in higher order bubbles

Identify features that do not meet with the user's...