INFORMATION MANAGEMENT Unit 2 SO 6 describe data flow diagrams (DFD);Define DFD; identify and...

INFORMATION MANAGEMENT

Unit 2 SO 6

describe data flow diagrams (DFD);

Define DFD; identify and describe the four symbols (elements): entity, process, data store, data flow; identify and describe the various levels of DFDs including context level DFD and first level detailed DFD.

What are Data Flow Diagrams (DFDs)?

A Data Flow Diagram (DFD) is a graphical representation of the "flow" of data through an Information System. It differs from the as it shows the flow of data through processes instead of hardware.

A Data Flow Diagram can also be used for the visualization of data processing (structured design).

Data flow diagrams were invented by Larry Constantine, the original developer of structured design, based on Martin and Estrin's "data flow graph" model of computation

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

DFD Symbols (Gane & Sarson)

Process

Data Flow

Data Store

Source/Sink (External Entity)

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

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

Rule 2: Process Can connect to any other symbol (including

another process symbol)

1.0

VerifyOrder

2.0

Assemble Order

Order Accepted OrderInventory Change

Process: Correct/Incorrect?5.0

Create Invoice

Services Perfomed Invoice

Apply InsurancePremium

Payment AmountPolicy Number

2.1

Calculate Gross Pay

Hours Worked Pay Rate

Data Flow

Is a path for data to move from one part of the Information System 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

Data Flow: Correct/Incorrect?

Courses

Students

ClassList

5.0

PostPayment

Customer Payment

D2 Daily Payments

6.0

Prepare Deposit

DailyPayment

Data Store

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

Labels should be noun phrases

StudentsD1

Rule: Data Store Must have at least one incoming and one

outgoing data flow

Daily Payments

D1

Customer Payment

Daily Payment

Data Store: Correct/Incorrect?

2.0

BookFlight

Passengers

FightRequest

D2 AccountsReceivable

PaymentDetail

3.0

PostPayment

InvoiceDetail

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 Source – Entity that supplies data to the system Sink – Entity that receives data from the system

CUSTOMER

1.0

VerifyOrder

Order

Invoice

Rule: Source/Sink

Must be connected to a process by a data flow

BANK

2.0

Prepare Deposit

BankDeposit

Source/Sink: Correct/Incorrect?

PAYROLLDEPARTMENT

EMPLOYEE

Paycheck

3.0

ApplyPayment

CUSTOMER

Payment

CUSTOMER

AccountsReceivable

Payment

Rules for Using DFD Symbols

Data Flow That Connects YES 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

List the errors of this DFD

E1

E1

P2

P1

1.0

2.0

DS1

DF2

DF2

DF6

DF4

DF3

DF1

DF5

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

0

Order System

SALESREP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

OrderReject Notice

PickingList

CompletedOrder

Payment Invoice

Commission Bank Deposit

CashReceiptsEntry

Context Diagram of Order System

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.

0

Order System

SALESREP

CUSTOMER WAREHOUSE

BANKACCOUNTING

Order

OrderReject Notice

PickingList

CompletedOrder

Payment Invoice

Commission Bank Deposit

CashReceiptsEntry

Context Diagram of Order System

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

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

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