Data Flow Diagrams (DFDs)

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Data Flow Diagrams (DFDs)

• Analysis tool
• System modeling
• Excellent documentation tool
• Data flow, aka, business process
• Provide a way to see the pattern
• Systems Thinking
• Systems View
• Systems Approach

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Data Flow Diagrams (DFDs) - continued

• Advantages for systems view, working with users
• Four simple symbols

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Data Flow Diagrams (DFDs) - continued

• Simple rule
• left to right, top to bottom, basically (like
  English)
• Show all processes
• data flows must start or end in a process
• beware of black holes - every process and data
  store must produce data
• no magic processes - must enter all needed data
  to get data out

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Data Flow Diagrams (DFDs) - continued

• Key Simple Symbols
• Most common error Trying to do too much

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DFD Example

• In the following example, a DFD will be created
  based on a paragraph about Bebop Records Co.s
  method of receiving and filling orders.
• In this example, the information necessary to
  create the DFD is provided for us. In Real Life,
  this information comes from extensive
  interviewing, document gathering, and other
  research.
• Depending upon the system being studied, the
  number of people working on it, etc., the
  development of a detailed DFD can take anywhere
  from a few hours to several months (paid for by
  your client with NO CODE TO SHOW FOR IT). Yet it
  is a very standard and meaningful part of system
  documentation.

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DFD Example
Bebop Records is a mail-order company that
distributes CDs and tapes at discount price 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 Orders file.
The clerk also prints an invoice and shipping
list for each order, which are forwarded to Order
Fulfillment.
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DFD Example - Step 1

• FIRST SENTENCE
• Bebop Records is a mail-order company that
  distributes CDs and tapes at discount price to
  record-club members.
• RESULT initial title
• Bebop Records

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DFD Example - Step 2

• SECOND SENTENCE
• 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.
• RESULT
• Bebop Records Order Processing

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DFD Example - Step 2 continued

• SECOND SENTENCE
• 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.
• RULES FOLLOWED
• left to right, top to bottom
• data flows start or end in a process

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DFD Example - Step 3

• THIRD SENTENCE
• If the sender is not a member, the clerk returns
  the order along with a membership application
  form.
• RESULT
• Bebop Records Order Processing

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DFD Example - Step 3 continued

• THIRD SENTENCE
• If the sender is not a member, the clerk returns
  the order along with a membership application
  form.
• RULES FOLLOWED
• shows all processes without conditions

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DFD Example - Step 4

• FOURTH SENTENCE
• If the customer is a member, the clerk verifies
  the order item data by checking the Item file.
• RESULT
• Bebop Records Order Processing

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DFD Example - Step 4 continued

• FOURTH SENTENCE
• If the customer is a member, the clerk verifies
  the order item data by checking the Item file.
• RULES FOLLOWED
• left to right, top to bottom
• data flows start or end in a process
• shows all processes without conditions

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DFD Example - Step 5

• FIFTH SENTENCE
• Then the clerk enters the order data and saves it
  to the Daily Orders file.
• RESULT

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DFD Example - Step 5 continued

• RESULT
• Bebop Records Order Processing

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DFD Example - Step 5 continued

• FIFTH SENTENCE
• Then the clerk enters the order data and saves it
  to the Daily Orders file.
• RULES FOLLOWED
• left to right, top to bottom
• data flows start or end in a process

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DFD Example - Step 6

• SIXTH SENTENCE
• The clerk also prints an invoice and shipping
  list for each order, which are forwarded to Order
  Fulfillment.
• RESULT

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DFD Example - Step 6 continued

• RESULT
• Bebop Records Order Processing

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DFD Example - Step 6 continued

• SIXTH SENTENCE
• The clerk also prints an invoice and shipping
  list for each order, which are forwarded to Order
  Fulfillment.
• RULES FOLLOWED
• left to right, top to bottom
• data flows start or end in a process
• shows all processes without conditions
• beware of black holes - every process and data
  store must produce data