# Create a data flow diagram

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Create a data flow diagram
DFD Examples Create a data flow diagram

Which way does the window face

How many legs do you see

Information flow In this task you will produce a simple data flow diagram Your task is to produce A diagram showing the information flow when sandwiches are sold, calculations are made, there is some sort of output. Details showing the terminators/entities, processes and data stores.

Information flow Click to move through this show.
Ordering a tuna roll Information flow Click to move through this show.

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.

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.

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.

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.

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

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

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

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.

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.

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.

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

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

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

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!

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

Before you start! A few rules to follow!!

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

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

Assignment – CDs by mail order
Bebop Records is a mail-order company that distributes CDs and tapes at discount prices to record club members. When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. If the sender is not a member, the clerk returns the order along with a membership application form. If the customer is a member, the clerk verifies the order item data by checking the Item file. Then the clerk enters the order data and saves it to the Daily Order file. The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

Annotating the text Processing
Annotating the text Data stores Annotating the text Entities

The end DFDs