1. Data Flow Diagramming Rules
Data stores and sources/sinks
no data flows between two data stores; must be a process in between
no data flows between a data store and a source or sink; must be a process in between
no data flows between two sources/sinks
such a data flow is not of interest, or
there is a process that moves that data

2. 2.1
Store
Customer
Data
2.1
Store
Customer
Data
Customer
Information
Customer
Information
Customer
Data
Customer
Data
Customer
Preferences D1
Customer Data D1
Customer Data
Customer
Preferences D2
Customer Preferences D2
Customer Preferences

3. 2.1
Store
Customer
Data
2.1
Store
Customer
Data
Customer
Information
Customer
Information
Customer
Data
Customer
Data D1
Customer Data
Customer
Data D1
Customer Data
2.2
Extract
Customer
Preferences
Customer
Preferences
Customer
Preferences D2
Customer Preferences D2
Customer Preferences

4. Customer
Customer
Information
Customer
2.0
Store
Customer
Data
Customer
Data D1
Customer Data
Customer
Data D1
Customer Data

5. Service
Information
Doctor
Medical
Billing
System
Diagnosis
Bill
Patient

6. Data Flow Diagramming Rules
Processes
a process must have at least one input
a process must have at least one output
a process name (except for the context level process) should be a verb phrase
usually three words: verb, modifier, noun
on a physical DFD, could be a complete sentence

7. Compile Statistics Demographic Data Gather Data Survey Responses
1.0
2.0
Compile
Statistics
Demographic
Data
Gather
Data
Survey
Responses
3.0
Analyze
Responses
Final
Report

8. BETTER Total Records Total Sales Records BETTER QA Process BETTER
2.0
2.0
Check
Customer
Credit
Visa
Authorization
BETTER
2.0
Total
Records
2.0
Total
Sales
Records
BETTER
2.0 QA
Process
2.0
BETTER
Inspect
Finished
Products

9. Data Flow Diagramming Rules
Data flows
data flows are unidirectional
a data flow may fork, delivering exactly the same data to two different destinations
two data flows may join to form one only if the original two are exactly the same
no recursive data flows
data flows (and data stores and sources/sinks) are labelled with noun phrases

10. 1.0
Take
Customer
Order
1.0
Take
Customer
Order
Customer
Order
Order
Total
Order
Information
Order
Total
Order
Information
2.0
Total
Daily
Sales
3.0
2.0
Total
Daily
Sales
3.0
Print
Delivery
Instructions
Print
Delivery
Instructions

11. 1.0
Take
Customer
Order
2.0
Lookup
Customer
Record
1.0
Take
Customer
Order
2.0
Lookup
Customer
Record
Customer
Order
Customer
Address
Customer
Order
Customer
Address
Customer
Information
3.0
3.0
Print
Delivery
Instructions
Print
Delivery
Instructions

12. 1.0
Calculate
Weekly
Sales
Daily
Sales
Cumulative
To-Date
Sales

13. Data Flow Diagramming Guidelines
The inputs to a process are different from the outputs
Every object in a DFD has a unique name

14. 1.0
Validate
Customer
Data
Customer
Data
Customer
Data
1.0
Validate
Customer
Data
Customer
Data
Valid
Customer
Data

15. 1.0
Get
Customer
Data
2.0
Take
Customer
Order
3.0
Process
Customer
Order
Order
Customer
Data
Customer
Data
1.0
Get
Customer
Data
2.0
Take
Customer
Order
3.0
Process
Customer
Order
Customer
Data
Order

16. Only if these are exactly the same
2.0
Take
Customer
Order
Customer
Data
1.0
Get
Customer
Data
3.0
Validate
Customer
Data
Customer
Data
Only if these are exactly the same

17. Employee D1
Employee Master
Employee
Record
Hours
Worked
1.0
2.0
Gross
Pay
Employee
Time
Record
Calculate
Gross
Pay
Calculate
Withholding
Amount D2
Employee Time File
Withholding
Employee
Record
4.0
3.0 D1
Employee Master
Net
Pay
Print
Employee
Paycheck
Calculate
Net
Pay
Check
Reconciliation
Record
Employee
Paycheck D3
Check Reconciliation
Employee

18. Employee D4
Withholding Tables
Number of
Dependents D1
Employee Master
Withholding
Rates
Hours
Worked
Employee
Record
5.0
Create
Time
Record
1.0
2.0
Gross
Pay
Calculate
Gross
Pay
Calculate
Withholding
Amount
Employee
Time Record
Employee
Time
Record
Withholding
Amount D2
Employee Time File
Gross
Pay D1
Employee Master
Employee
Record
4.0
3.0
6.0
Net
Pay
Print
Employee
Paycheck
Calculate
Net
Pay
Paycheck
Information
Reconcile
Pay
Check
Employee
Paycheck
Check
Reconciliation
Record
Employee D3
Check Reconciliation

19. Data Elements Indivisible pieces of data
Data flows and data stores are made up of data elements
Like attributes on an ER diagram
The data elements of a data flow flowing in or out of a data store must be a subset of the data elements in that data store