Lesson#6 DFD

8/13/2019 Lesson#6 DFD

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How to :

Data Flow Diagrams(DFDs)


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Data Flow Diagrams (DFDs)

Data flow diagram

(DFD) is a picture of

the movement of

data between

external entities and

the processes and

data stores within a

system

1.0

Check

Status

2.0

Issue

Status

Messages

3.0

Generate

Shipping

Order

ACCOUNTING

CUSTOMER WAREHOUSE

4.0

Manage

AccountsReceivable

5.0

Produce

Reports

Order In-Stock Request

Status Data

Status

Message

PendingOrdersD1

OrderData

Order Data

Shipping

Order

ShippingConfirmation

Invoice

Payment

Accounts

ReceivableD2

Accounting Data Accounts Receivable Data

Order Data

Inventory

Reports


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DFD Symbols (Gane & Sarson)

Process

DataFlow

Data

Store

Source/Sink (External Entity)


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Process

Work or actions performed on data (inside thesystem)

Labels should be verb phrases

Receives input data and produces output

1.0

Produce

Grade

Report

Grade Detail Grade Report


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Rule 1: Process

Can have more than one outgoing data flowor more than one incoming data flow

1.0

Grade

Student

Work

Submitted Work Graded Work

Student Grade

3.0

Calculated

Gross

Pay

Hours Worked

Pay Rate

Gross Pay


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Rule 2: Process

Can connect to any other symbol (includinganother process symbol)

1.0

Verify

Order

2.0

Assemble

Order

Order Accepted OrderInventory

Change


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Process: Correct/Incorrect?

5.0

Create

Invoice

Services Perfomed Invoice

Apply

Insurance

Premium

Payment AmountPolicy Number

2.1

Calculate

Gross

Pay

Hours Worked Pay Rate


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Data Flow

Is a path for data to move from one part of theIS to another

Arrows depicting movement of data Can represent flow between process and data

store by two separate arrows

Deposit

2.1

Post

Payment

Accounts

ReceivableD1

Payment Detail

Invoice Detail


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Data Flow: Correct/Incorrect?

Courses

Students

Class

List

5.0

PostPayment

Customer

Payment

D2 Daily Payments

6.0

Prepare

Deposit

Daily

Payment


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Data Store

Is used in a DFD to represent data that the

system stores Labels should be noun phrases

StudentsD1


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Rule: Data Store

Must have at least one incoming and oneoutgoing data flow

Daily

PaymentsD1

Customer Payment

Daily Payment


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Data Store: Correct/Incorrect?

2.0

Book

Flight

Passengers

Fight

Request

D2 Accounts

Receivable

PaymentDetail

3.0

PostPayment

InvoiceDetail


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Source/Sink (External Entity)

External entity that is origin or destination ofdata (outside the system)

Is the singular form of a department, outsideorganisation, other IS, or person

Labels should be noun phrases

CUSTOMER

1.0

Verify

Order

Order

Invoice

SourceEntity that supplies data to the

system

SinkEntity that receives data from the

system


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Rule: Source/Sink

Must be connected to a process by a data flow

BANK

2.0

Prepare

Deposit

Bank

Deposit


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Source/Sink: Correct/Incorrect?

PAYROLL

DEPARTMENT

EMPLOYEE

Paycheck

3.0

Apply

Payment

CUSTOMER

Payment

CUSTOMER

Accounts

Receivable

Payment


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Rules for Using DFD Symbols

Data Flow That ConnectsYES NO

A process to another process

A process to an external entity

A process to a data store

An external entity to another external entity

An external entity to a data store

A data store to another data store


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List the errors of this DFD

E1

E1

P2

P1

1.0

2.0

DS1

DF2

DF2

DF6

DF4

DF3

DF1

DF5


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Context Diagram

Top-level view of IS

Shows the system boundaries, external entities that

interact with the system, and major information flows

between entities and the system. Example: Order system that a company uses to

enter orders and apply payments against a

customers balance


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0

Order

System

SALES

REP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

Order

Reject

Notice

Picking

List

CompletedOrder

Payment Invoice

Commission BankDeposit

CashReceipts

Entry

Context Diagram

of Order System


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Level-0 DFD

Shows the systems major processes, data flows,

and data stores at a high level of abstraction

When the Context Diagram is expanded into DFD

level-0, all the connections that flow into and out ofprocess 0 needs to be retained.


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0

Order

System

SALES

REP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

Order

Reject

Notice

Picking

List

CompletedOrder

Payment Invoice

Commission BankDeposit

CashReceipts

Entry

Context Diagram

of Order System


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1.0

FillOrder

2.0

Create

Invoice

3.0

Apply

Payment

SALES

REP BANK ACCOUNTING

CUSTOMER WAREHOUSE

Order

Order

Reject

Notice

Picking List

Accounts

ReceivableD1

Invoice

Invoice

Invoice

DetailPayment

Detail

Payment

Commission Bank Deposit Cash Receipts Entry

Completed

Order

Level-0 DFD of

Order System


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Lower-Level Diagrams

Functional DecompositionAn iterative process of breaking a system description

down into finer and finer detail

Uses a series of increasingly detailed DFDs to

describe an IS

Balancing The conservation of inputs and outputs to a data flow

process when that process is decomposed to a lower

level Ensures that the input and output data flows of the

parent DFD are maintained on the child DFD


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Strategies for Developing DFDs

Top-down strategy

Create the high-level diagrams (Context

Diagram), then low-level diagrams (Level-0

diagram), and so on

Bottom-up strategy

Create the low-level diagrams, then higher-

level diagrams


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Exercise:

Precision Tools sells a line of high-quality woodworkingtools. When customers place orders on the companys

Web site, the system checks to see if the items are in

stock, issues a status message to the customer, and

generates a shipping order to the warehouse, which fills the

order. When the order is shipped, the customer is billed.The system also produces various reports.

Draw a context diagram for the order system

Draw DFD diagram 0 for the order system


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Identify Entities,Process,Data Stores & Data Flow

Entities

Customer

Warehouse

Accounting

Processes

1.0 Check Status 2.0 Issue Status Messages

3.0 Generate Shipping Order

4.0 Manage Accounts

Receivable

5.0 Produce Reports

Data Stores

D1 Pending Orders

D2 Accounts Receivable

Data Flows Order

In-Stock Request

Order Data

Status Data

Status Message Shipping Order

Order Data

Invoice

Shipping Confirmation

Payment

Accounting Data

Accounts Receivable Data

Order Data

Inventory Reports

1.0

2.0

3.0

4.0

5.0


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ACCOUNTING

WAREHOUSECUSTOMER

0

Order

System

Order

Payment

In-Stock

Request

Status

Message

Invoice Shipping Confirmation

Shipping

Order

Inventory

Reports

Context

Diagram of

Order

System


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1.0

Check

Status

2.0

Issue

Status

Messages

3.0

GenerateShipping

Order

ACCOUNTING

CUSTOMER WAREHOUSE

4.0

Manage

Accounts

Receivable

5.0

Produce

Reports

Order In-Stock Request

Status Data

Status

Message

Pending

OrdersD1

Order

Data

Order Data

Shipping

Order

Shipping

Confirmation

Invoice

Payment

Accounts

ReceivableD2

Accounting Data Accounts Receivable Data

Order Data

Inventory

ReportsLevel-0 of

Order

System

Lesson#6 DFD

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