Data Flow Diagrams

"Business process flow"not a Flow Chart

How are they developed?

• Interviews with business staff

• Observation of daily routines

• Scrutiny of paper forms, routing documents

• Research procedure manuals

• Gain understanding of processes

• Describe the flow of data in process

DFD Rules

• Always begin (or end) with a process

• All processes must produce data

• Describe data flow or business flow

• Flow left to right, top to bottom

• Do not place conditions

• Every process produces data

Example 1a

• Salesperson verifies customer's charge account when customer orders a computer

Salespersonverifiesaccount

Customer tableCustomerordersComputer

Orderrequest

Accountdata

External Entity

Business Process

Data Flow

Data Source

Example 1b

• Salesperson verifies customer's charge account when customer orders a computer, and opens a new account if necessary

Salespersonverifiesaccount

Customer tableCustomerordersComputer

Orderrequest

Accountdata

Add new account

Example 1c

• Salesperson verifies customer's charge account when customer orders a computer, and opens a new account if necessary.

• Next, salesperson verifies the computer is in inventory

• Finally, the order is entered and the computer is shipped

Salespersonverifiesaccount

Customer tableCustomerordersComputer

Orderrequest

Accountdata

Add new account

Inventory table

Invoice table

Salespersonverifies

on-hand qty

Orderdetails

Salespersoncompletesorder

itemdetails

invoicedetails