DFD Examples

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DFD Examples

• Create a data flow diagram

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Which way does the window face
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How many legs do you see
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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.

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Ordering a tuna roll

• Information flow
• Click to move through this show.

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Tuna roll please!
Ordering some lunch
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.
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Ordering some lunch
Order 1 x Tuna roll
Order 1 x Tuna roll
The waitresses write this down and passes the
order to the chef.
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Ordering some lunch
Order 1 x Tuna roll
The chef gets the order and makes the roll. The
roll is then passed back to the waitress.
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Ordering some lunch
Coffee Control 1 tuna roll RM 2.99 Thank you
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.
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Ordering some lunch
When the food arrives from the chef, the waitress
gives it to the customer.
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Information flow

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

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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

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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.
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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.
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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.
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DFD Symbols
External Entity
Customer
Chef
Bill
Flow of Data
Process
Preparing a bill
Menu
Data Store
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Who are the ENTITIES?
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
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What is a DATA STORE
The menu or price list keeps a record of prices
it is a data store.
The menu is a DATA STORE
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Who is a process?
The waitress processes the order
The waitress is a process
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!
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1. order
5. invoice
2. order
6. payment
8. Tuna
7. receipt
9. Tuna
3. query price
4. price
The arrows indicate data flows
The final Data Flow Diagram
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Before you start!

• A few rules to follow!!

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Customer
Chef
X wrong!
There must always be a process between entities!
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Order sandwich
Customer
Chef
X wrong!
Information flows must NEVER cross!
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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.
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Annotating the textProcessing
Annotating the textData stores
Annotating the textEntities
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The end

• DFDs