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Data flow diagrams for dummies

Date post: 09-May-2015
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Our team at Cazoomi uses Data Flow Diagrams (DFD) daily. DFDs are a picture of the movement of data between external entities and the processes and data stores within a system. http://www.cazoomi.com ~Clint @cazoomi
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How to : Data Flow Diagrams (DFDs)
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Page 1: Data flow diagrams for dummies

How to :Data Flow Diagrams (DFDs)

Page 2: Data flow diagrams for dummies

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

CheckStatus

2.0

IssueStatus

Messages

3.0

GenerateShipping

Order

ACCOUNTING

CUSTOMER WAREHOUSE

4.0

Manage Accounts

Receivable5.0

ProduceReports

Order In-Stock Request

Status Data

Status Message

PendingOrdersD1

Order Data

Order Data

Shipping Order

Shipping Confirmation

Invoice

Payment

Accounts ReceivableD2

Accounting Data Accounts Receivable Data

Order Data

Inventory Reports

Page 3: Data flow diagrams for dummies

DFD Symbols (Gane & Sarson)

Process

Data Flow

Data Store

Source/Sink (External Entity)

Page 4: Data flow diagrams for dummies

Process

Work or actions performed on data (inside the system)

Labels should be verb phrases Receives input data and produces output

1.0

ProduceGradeReport

Grade Detail Grade Report

Page 5: Data flow diagrams for dummies

Rule 1: Process

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

1.0

GradeStudent Work

Submitted WorkGraded Work

Student Grade

3.0

Calculated Gross Pay

Hours Worked

Pay RateGross Pay

Page 6: Data flow diagrams for dummies

Rule 2: Process

Can connect to any other symbol (including another process symbol)

1.0

VerifyOrder

2.0

Assemble Order

Order Accepted OrderInventory Change

Page 7: Data flow diagrams for dummies

Process: Correct/Incorrect?5.0

Create Invoice

Services Perfomed Invoice

Apply InsurancePremium

Payment AmountPolicy Number

2.1

Calculate Gross Pay

Hours Worked Pay Rate

Page 8: Data flow diagrams for dummies

Data Flow

Is a path for data to move from one part of the IS 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 Receivable

D1

Payment Detail

Invoice Detail

Page 9: Data flow diagrams for dummies

Data Flow: Correct/Incorrect?

Courses

Students

ClassList

5.0

PostPayment

Customer Payment

D2 Daily Payments

6.0

Prepare Deposit

DailyPayment

Page 10: Data flow diagrams for dummies

Data Store

Is used in a DFD to represent data that the system stores

Labels should be noun phrases

StudentsD1

Page 11: Data flow diagrams for dummies

Rule: Data Store

Must have at least one incoming and one outgoing data flow

Daily Payments

D1

Customer Payment

Daily Payment

Page 12: Data flow diagrams for dummies

Data Store: Correct/Incorrect?

2.0

BookFlight

Passengers

FightRequest

D2 AccountsReceivable

PaymentDetail

3.0

PostPayment

InvoiceDetail

Page 13: Data flow diagrams for dummies

Source/Sink (External Entity)

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

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

Labels should be noun phrases

CUSTOMER

1.0

VerifyOrder

Order

Invoice

Source – Entity that supplies data to the system

Sink – Entity that receives data from the system

Page 14: Data flow diagrams for dummies

Rule: Source/Sink

Must be connected to a process by a data flow

BANK

2.0

Prepare Deposit

BankDeposit

Page 15: Data flow diagrams for dummies

Source/Sink: Correct/Incorrect?

PAYROLLDEPARTMENT

EMPLOYEE

Paycheck

3.0

ApplyPayment

CUSTOMER

Payment

CUSTOMER

AccountsReceivable

Payment

Page 16: Data flow diagrams for dummies

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

Page 17: Data flow diagrams for dummies

List the errors of this DFD

E1

E1

P2

P1

1.0

2.0

DS1

DF2

DF2

DF6

DF4

DF3

DF1

DF5

Page 18: Data flow diagrams for dummies

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 customer’s balance

Page 19: Data flow diagrams for dummies

0

Order System

SALESREP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

OrderReject Notice

PickingList

CompletedOrder

Payment Invoice

Commission Bank Deposit

CashReceiptsEntry

Context Diagram of Order System

Page 20: Data flow diagrams for dummies

Level-0 DFD

Shows the system’s 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 of process 0 needs to be retained.

Page 21: Data flow diagrams for dummies

0

Order System

SALESREP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

OrderReject Notice

PickingList

CompletedOrder

Payment Invoice

Commission Bank Deposit

CashReceiptsEntry

Context Diagram of Order System

Page 22: Data flow diagrams for dummies

1.0

Fill Order

2.0

CreateInvoice

3.0

ApplyPayment

SALESREP

BANK ACCOUNTING

CUSTOMER WAREHOUSE

Order

Order RejectNotice

Picking List

AccountsReceivableD1

Invoice

Invoice

Invoice DetailPayment

Detail

Payment

Commission Bank Deposit Cash Receipts Entry

Completed Order

Level-0 DFD of Order System

Page 23: Data flow diagrams for dummies

Lower-Level Diagrams

Functional Decomposition An 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

Page 24: Data flow diagrams for dummies

Strategies for Developing DFDs

Top-down strategyCreate the high-level diagrams (Context

Diagram), then low-level diagrams (Level-0 diagram), and so on

Bottom-up strategyCreate the low-level diagrams, then higher-

level diagrams

Page 25: Data flow diagrams for dummies

Exercise:Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s 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

Page 26: Data flow diagrams for dummies

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

Page 27: Data flow diagrams for dummies

ACCOUNTING

WAREHOUSECUSTOMER

0

Order System

Order

Payment

In-StockRequest

StatusMessage

Invoice Shipping Confirmation

Shipping Order

Inventory Reports

Context Diagram of Order System

Page 28: Data flow diagrams for dummies

1.0

CheckStatus

2.0

IssueStatus

Messages

3.0

GenerateShipping

Order

ACCOUNTING

CUSTOMER WAREHOUSE

4.0

Manage Accounts

Receivable5.0

ProduceReports

Order In-Stock Request

Status Data

Status Message

PendingOrdersD1

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


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