CAPE INFORMATION TECHNOLOGY – Unit 2
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Transcript of CAPE INFORMATION TECHNOLOGY – Unit 2
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