1. DFD examples

2. steps Create a list of activities
Construct Context Level DFD (identifies external entities and processes)
Construct Level 0 DFD (identifies manageable sub process )
Construct Level 1- n DFD (identifies actual data flows and data stores )
Check against rules of DFD

3. External entities … noun
Data flows .. Name of data
Process ..verb phrase ( system name , sub sytem name)
Data store ..noun

4. (draw your context diagram)

5. Level-0 DFD

6. Consider the following DFD. List two errors on this DFD
1.0 P2 E1
DF5
DS1
DF6
DF3
DF1
DF4
2.0 P1
DF2 E2

7. Logizian Analyst edition

8. Ordering a tuna roll

9. Ordering some lunch Tuna roll please!
The customer
A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll.

10. The waitresses write this down and passes the order to the chef.
Ordering some lunch
The waitresses
Order
1 x Tuna roll
Order
1 x Tuna roll
The waitresses write this down and passes the order to the chef.

11. Ordering some lunch Order
The chef
Order
1 x Tuna roll
The chef gets the order and makes the roll. The roll is then passed back to the waitress.

12. The customer pays their bill.
Ordering some lunch
Coffee Control
1 tuna roll
RM 2.99
Thank you
The waitresses
The customer
Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the cash till. This shows how much the customer owes.
The customer pays their bill.

13. Ordering some lunch
The waitresses
The customer
When the food arrives from the chef, the waitress gives it to the customer.

14. Information flow
The next few slides demonstrate how to produce the data flow diagram – this example is for ordering a tuna roll.

15. Analyse the problem
Put a square around any inputs or outputs involved - these are entities.
Circle any data stores.
Underline any processing that takes place
Sketch out the information flow, joining up the people (entities, the processing and the data stores

16. Square around inputs and outputs
A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

17. Circle data stores
A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

18. Underline any processing
A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

19. DFD Symbols External Entity Flow of Data Process Data Store Customer
Chef
Bill
Flow of Data
Process
Preparing a bill
Menu
Data Store

20. The customer and the chef are ENTITIES
Who are the ENTITIES?
Customer
Chef
The customer is a source of information – the person who start the whole process off.
The chef is a destination of the information.
The customer and the chef are ENTITIES

21. What is a DATA STORE The menu is a DATA STORE
Customer
Chef
The menu or price list keeps a record of prices – it is a data store.
Sandwich prices
The menu is a DATA STORE

22. The waitress is a process
Who is a process?
Order sandwich
Customer
Chef
The waitress processes the order
The waitress is a process
Sandwich prices
The waitress is not shown as an entity because she does not produce or receive information (ultimately – the order goes to the chef!!). She is not a data SOURCE or SINK!

23. The arrows indicate data flows
1. order
Customer
Order sandwich
5. invoice
2. order
Chef
6. payment
8. Tuna
7. receipt
9. Tuna
4. price
3. query price
Sandwich prices
The arrows indicate data flows
The final Data Flow Diagram

24. Before you start!
A few rules to follow!!

25. There must always be a process between entities!
Customer
Chef
X wrong!
There must always be a process between entities!

26. Information flows must NEVER cross!
Customer
Order sandwich
Chef
X wrong!
Sandwich prices
Information flows must NEVER cross!