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Data Flow Diagramming

Data Flow Diagramming

Represent processes …that capture, manipulate, store, & distribute data

…between a system & its environment

… & among system components.

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2.0 ConnectorShow that data flow continues to another process

Data Flow Diagramming

a process modeling technique

retrieval

storage#

Process

Data StoreinputSource

Sinkoutput

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Context Diagram An overview Represents the System Scope

OrderEntry

System

0

Customers

InventorySystem

SalesManager

Sales orders

Acceptedsales order file

Rejectedsales order report

Level-0 Diagram

Acceptedsales order file

Rejected sales order report

Item numbers

Item prices

Rejected sales order file

Sorted rejected sales order fileInventory

System

SalesManager

1.0

Screensales orders

3.0

Preparerejected

sales orderreport

2.0

Sortrejected

sales orderfile

Master itemnumber list

Master price list

Sales ordersCustomers

Sales orders

Acceptedsales order

file Master pricelist

Master itemnumber list

Item numbers

Item prices

Verified item numbers

Rejected sales order file2.0

Customers

InventorySystem

1.1

Verifyitem

number

1.2

Verifyprice

Level 1 Diagram (for Process 1.0)aka: Diagram 1.0

Master price list

Master itemnumber list

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DFD Rules

Naming Conventions

Processes− Verb phrase = verb + object− e.g. ValidateAccount, CalculateTax

Data Flows− Noun/noun phrase = adj + object− e.g. payment, verified payment

Data Stores− Noun/noun phrase = adj + object− e.g. Employee, HourlyEmployee

External Agent− Noun/noun phrase = adj + object− Customer, Regional Warehouse, e.g.

Billing System

Rules By TypeProcess− Must have both inputs & outputs− At least one output must be different

Data Flow− Has only one direction− Cannot return directly to the process

Data must be moved via a process

DFDs should:Accurately represents the systemBe BalancedBe ConsistentBe Readable

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Other Concepts

Retrieval

Updates Insert Update Delete

Packet

New item Inventory Item

Quantity on hand Inventory Item

Purged item Inventory Item

Price Inventory ItemPrice Inventory Item

Item #

#

P1.1

applicationStudent

resume #

P1.1

Application & resumeStudent

When items travel together

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DFD Practice

Draw a Level-0 Diagram Notes:− Time card ≠ Time sheet− Treat “Employee” as external to this system.

Employees provide the departmental secretary with their weekly timecards. The secretary prepares a weekly time sheet that lists each employee, the total hours worked, and the hourly rate. The timecards are filed in a Time card history file.

The departmental supervisor signs the time sheet if everything seems to be in order. If any figures are unacceptable, the supervisor returns the sheet to the secretary. The acceptable sheets from the departments are sent in the company mail to the accounting department.

The accounting clerk uses the acceptable time sheets to calculate payroll earnings and writes the earnings on the time sheets.

Another clerk uses the time sheets to prepare the payroll checks, which are forwarded to the employees. After this operation, the time sheets are filed in an off-line Time sheet history file.