1. DFD examples

2. Creating DFDs Define Entities Define Processes
External entities represent persons, processes or machines which produce data to be used by the system or receive data that is output by the system
Examples: Student, Customer, Client
Define Processes
Processes are discrete actions that transform input data to output data
Examples: Create Student Record, Calculate Purchase Cost, Register Client
Student
2.1
Create Student Record

3. Creating DFDs (cont’d)
Define Data Stores
Data stores are temporary or permanent repositories of information that are inputs to or outputs of processes
Examples: Student Master, Client List
Define Data Flows
Data flows represent the transfer of data over time from one “place” (entity, process, data store) to another
Examples: New Student Information (from Student, to Student Master)
Student Master D3
New Student Information

4. Creating DFDs (cont’d)
Define the System
A system is the collection of all business processes which perform tasks or produce outputs we care about. It is “what happens.”
The system is a single process, connected to external entities
Represented in a “Context Diagram”
Define Subsystems
A subsystem gives a more detailed view individual processes contained in the context diagram
Includes data stores, more elementary processes

5. DFDs Created by Top-Down Analysis
Create a narrative: description of system
Create a Context Diagram that contains a single process (“the system”) and all entities which share data with the system
Explode the “parent” context diagram to produce a Diagram 0 (“child”) DFD
Create Diagram 1, 2, …, n DFDs that represent “explosions” of Diagram 0, 1, …, n-1 DFDs until a diagram has only “primitive” processes
Create process descriptions to be implemented by application programs: queries, macros, reports, programming languages
Context Diagram
Diagram 0 DFD
Diagram 1 DFDs
Diagram n DFDs
Narrative
E-R Diagram
Process Descriptions

6. Where to Begin Creating DFDs
Start with the data flow from an external entity and work forwards
Start with the data flow to an external entity and work backwards
Examine the data flows into or out of a data store
Examine data flows, entity connections and data stores associated with a particular process
Note fuzzy, ill-defined areas of the system for further clarification

7. What to Avoid in DFDs Processes with no outputs or no inputs4
Perform Repair
Processes with no outputs or
no inputs
Processes whose inputs are obviously inadequate to yield outputs
Connecting data stores directly to each other
Class List
Courses
Students
Having data flows terminate at data stores
Connecting entities to anything other than processes
Payroll Department
Employees
Making the data flow diagram too cluttered (e.g.  9 processes) 1 2 3
Many processes with a single
input and output (linear flow)
Process A
Process B
Process C

8. Creating Data Flow Diagrams Lemonade Stand Example

9. Creating Data Flow Diagrams
Example
Steps:
The operations of a simple lemonade stand will be used to demonstrate the creation of dataflow diagrams.
Create a list of activities
Old way: no Use-Case Diagram
New way: use Use-Case Diagram
Construct Context Level DFD (identifies sources and sink)
Construct Level 0 DFD (identifies manageable sub processes )
Construct Level 1- n DFD (identifies actual data flows and data stores )

10. Creating Data Flow Diagrams
Example
Create a list of activities
Think through the activities that take place at a lemonade stand.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product

11. Creating Data Flow Diagrams
Example
Create a list of activities
Also think of the additional activities needed to support the basic activities.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor

12. Creating Data Flow Diagrams
Example
Create a list of activities
Group these activities in some logical fashion, possibly functional areas.
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor

13. Creating Data Flow Diagrams
Example
Construct Context Level DFD (identifies sources and sink)
Create a context level diagram identifying the sources and sinks (users).
Context Level DFD
Sales Forecast
CUSTOMER
0.0
Lemonade System
EMPLOYEE
Order
Production Schedule
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Product Served
Pay
Payment
Time Worked
Received Goods
Payment
Purchase Order
VENDOR

14. Creating Data Flow Diagrams
Example
Construct Level 0 DFD (identifies manageable sub processes )
Create a level 0 diagram identifying the logical subsystems that may exist.
Level 0 DFD
1.0
Sale
Sales Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Customer Order
Product Ordered
CUSTOMER
Payment
2.0
Production
EMPLOYEE
Production Schedule
Product Served
Inventory
Received Goods
VENDOR
3.0
Procure-ment
Purchase Order
Order Decisions
Payment
Pay
Time Worked
4.0
Payroll

15. Creating Data Flow Diagrams
Example
Construct Level 1- n DFD (identifies actual data flows and data stores )
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
CUSTOMER
Customer Order
Request for Forecast
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
ORDER
1.1
Record Order
1.3
Produce Sales Forecast
Severed Order
Payment
Sales Forecast
1.2
Receive Payment
PAYMENT

16. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Product Order
ORDER
2.1
Serve Product
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity Severed
RAW MATERIALS
Production Schedule
2.2
Produce Product
Quantity Used
INVENTORTY
Production Data
2.3
Store
Product
Quantity Produced & Location Stored

17. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Order Decision
PURCHASE ORDER
3.1
Produce Purchase Order
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Quantity On-Hand
RAW MATERIALS
Quantity Received
Received Goods
3.2
Receive Items
RECEIVED ITEMS
Payment Approval
3.3
Pay Vendor
VENDOR
Payment

18. Creating Data Flow Diagrams
Example
Construct Level 1 (continued)
Create a level 1 decomposing the processes in level 0 and identifying data stores.
Level 1 DFD
Time Worked
TIME CARDS
4.1
Record Time Worked
Customer Order
Serve Product
Collect Payment
Produce Product
Store Product
Order Raw Materials
Pay for Raw Materials
Pay for Labor
Employee ID
EMPLOYEE
Payroll Request
4.2
Calculate Payroll
Unpaid time cards
PAYROLL
Payment Approval
4.3
Pay Employee
PAYMENTS
Payment

19. Process Decomposition
1.0
Sale
1.1
Record Order
1.2
Receive Payment
2.0
Production
2.1
Serve Product
2.2
Produce Product
2.3
Store
Product
0.0
Lemonade System
3.0
Procure-ment
3.1
Produce Purchase Order
3.2
Receive Items
3.3
Pay Vendor
4.0
Payroll
4.1
Record Time Worked
4.2
Calculate Payroll
4.3
Pay Employee
Context Level
Level 0
Level 1

20. DFD Example: Bus Garage Repairs
Buses come to a garage for repairs.
A mechanic and helper perform the repair, record the reason for the repair and record the total cost of all parts used on a Shop Repair Order.
Information on labor, parts and repair outcome is used for billing by the Accounting Department, parts monitoring by the inventory management computer system and a performance review by the supervisor.
Key process (“the system”): performing repairs and storing information related to repairs
External Entities: Bus, Mechanic, Helper, Supervisor, Inventory Management System, Accounting Department, etc.
Processes:
Record Bus ID and reason for repair
Determine parts needed
Perform repair
Calculate parts extended and total cost
Record labor hours, cost

21. DFD Example: Bus Garage Repairs (cont’d)
Data stores:
Personnel file
Repairs file
Bus master list
Parts list
Data flows:
Repair order
Bus record
Parts record
Employee timecard
Invoices

22. Bus Garage Context Diagram
Mechanical problem
to be repaired
Fixed mechanical
problems
Supervisor
Helper
Bus Repair Process
Repair summary
Labor
List of parts used
Inventory Management System
Labor
Labor, parts cost details
Mechanic
Accounting