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Data Flow Diagram Notations

Yourdon and Coad

Process Notations

Gane and Sarson

Process Notation

Yourdon and Coad

Datastore Notation

Gane and Sarson

Datastore Notations

Process

A process transforms incoming

data flow into outgoing data flow.

Data StoreData stores are repositories of

data in the system. They are

sometimes also referred to as

files.

DataflowDataflows are pipelinesthrough which packets ofinformation flow. Labelthe arrows with thename of the data thatmoves through it.

External Entity

External entities are objects outside the

system, with which the system

communicates. External entities aresources and destinations of the system's

inputs and outputs.

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DataFlow Diagrams

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Data Flow Diagram LayersDraw

Data flow diagrams are drawn in several

nested layers

A single process node on a high level

diagram can be expanded to show a more

detailed data flow diagram.

Draw the context diagram first, followed by

various layers of data flow diagrams.

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DFD Layers

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Context Diagrams

A context diagram is a top level (also known as Level 0) data flow diagram. It only contains one

process node (process 0) that generalizes the function of the entire system in relationship to

external entities.

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DFD levels

The first level DFD shows the main processes within thesystem. Each of these processes can be broken into

further processes until you reach pseudocode.

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Context Diagram- Registration

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Level 0 Data Flow Diagram

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Explosion of Process 4

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Level 0 DFD ATM

ATM

member

banks

User

Printer

account

database

Transaction requests

Balance

Information

receipt

request

display

Account dataInformation

request

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A level 1 DFD

1.

Validate

Customer

access

3.

Obtain

Details oftransaction

4.

Validate

transaction

2.

Reject

transaction

\and end session

customer

Network

directory

CustomersCard details

PIN

select

options

Rejection

message

Access

map

Access

permissions

Rejection

message

Transaction

request

Access

authorization

Printer/display

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A level 2 DFD

1.1

Read

Details

From

card

1.3

Request

Pin

And match

Max 3 attempts

1.2

Check

Expiry date

And bank group

customer

Network

directory

CustomersCard details

PIN

Cannot

Read

card

Card

data

Access

mapInvalid pin

CardValidation data

Encoded

pin

Printer/display

Access

authorization

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Get

deposit

Get

inquiry

Do

deposit

transaction

Another Approach to the

ATM Level 1

account #& deposit

account #

User

accountdata

Validate

inquiry

Create

account

summary

error

error

Printer

member

banks

bank name

account #

Validate

deposit

balancequery

account #& deposit

Make

inquiry

account

database

deposittransaction

Display

account

accountdata

accountdisplay