CTIS 359 PRINCIPLES OF SOFTWARE ENGINEERING

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CTIS 359 PRINCIPLES OF SOFTWARE ENGINEERING

• DATA FLOW DIAGRAM (DFD)

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LOGICAL PROCESS MODELING

• The physical model of a system can be thought of
  as the system itself. (hardware, software,
  connections, processes, data flows, data, etc.)
• The logical model of a system can be thought of
  implementation independent from any technical
  approach.

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LOGICAL PROCESS MODELING

• Model the activity of peeling an apple
• Get the apple.
• Get the peeling device.
• Wash the apple.
• Hold the apple.
• Peel the apple with with the peeling device.
• Discard the peel.
• Process the apple into desired form.

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LOGICAL PROCESS MODELING

• Source Marakas, Systems Analysis and Design,2nd
  2006 Edition

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PHYSICAL PROCESS MODELING EXAMPLE

• The physical model would look like
• Get the apple by removing it from the fruit
  drawer in the refrigerator using either hand.
• Get the paring knife from the upper left-hand
  kitchen drawer using either hand after setting
  the apple dowm.
• Etc.

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DATA FLOW DIAGRAM (DFD)

• A graphical tool that depicts the sequence of
  processes contained within a specific system
  boundary and the flow of data through that
  system.
• We can visualize the flow of data through the
  system and logical expression of events contained
  within it.
• It does not answer the question What goes on
  inside the process?
  
  
  

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DFD SYMBOLS

• Four basic symbols
• Process
• Data Flow
• Data Store
• External Entity
• Two popular symbol sets
• Gane and Sarson
• DeMarco and Yourson

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DFD SYMBOLS

• Source Marakas, Systems Analysis and Design,2nd
  2006 Edition

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DFD COMPONENTS

• Data Flow
• Represented by a line with arrowhead indicating
  direction of flow
• Data in motion
• Use noun to name the data content

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DFD COMPONENTS

• Data Store
• Represents a repository for data recorded within
  the system
• Data at rest

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DFD COMPONENTS

• Process
• Transform data into another form
• Process inputs to create a set of output data
  flows
• Using the input as output in its same basic form
• Reorganize the inputs

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DFD COMPONENTS

• External agent
• Someone or something interacts with the system
  but resides outside the system boundary
• Source serve as the origin of data flowing into
  the system
• Sink represents a destination for data flowing
  out from the system

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DFD HIERARCHY

• System is composed of a decomposable set of
  subsystems.
• By creating a top-down decomposed hierarchy of
  diagrams, each with a greater degree of detail
  than the last, we can understand the complexity
  of the system.

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DFD HIERARCHY

• Source Marakas, Systems Analysis and Design,2nd
  2006 Edition

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CONTEXT LEVEL DIAGRAM

• Shows the system boundary
• Contain only one process, labeled with the name
  of the system, assigned a zero as its identifier
• Data flow connects the process to its source and
  sink entities

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CONTEXT LEVEL DIAGRAM

• Source Marakas, Systems Analysis and Design,2nd
  2006 Edition

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LEVEL-0 DFD

• More detail than the context diagram
• Major processes within the system
• Sequence of those processes
• Data stores accessed by those processes
• Source and sink entities that interact with the
  system

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LEVEL-0 DFD

• Source Marakas, Systems Analysis and Design,2nd
  2006 Edition

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DFD GUIDELINES

• Establish system boundary.
• Label processes and data flows with sufficient
  information.
• Think WHAT and not HOW.
• Think data FLOW, not control.

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DFD RULES

• A process cannot have only outputs
• A process cannot have only inputs
• The inputs to a process must be sufficient to
  produce the outputs
• All data stores must be connected to at least one
  process
• A data store cannot be connected to a source or
  sink
• A data flow can have only one direction of flow
• Data cannot flow directly back into the process
  it has just left
• All data flows must be named using a noun phrase

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DFD EXAMPLE

• We are going to develop a system to record orders
  for pizza. When customers call the store, they
  are asked their phone number. When the number is
  typed in into a computer, the name, address, and
  last order data is automatically brought up on
  the screen. If the customer is new, he is added
  to the system. Once the order is taken, the
  total, including tax and delivery is
  calculated.Then the order is given to the cook. A
  receipt is printed. Occasionally, coupons are
  printed so the customer can get a discount.
  Drivers who make deliverables give customers a
  copy of the receipt an and a coupon (if any).
  Weekley totals are kept for comparison with last
  years performance.

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DFD EXAMPLE

• Write a summary of business activities
• Draw a logical context level DFD
• Explode the logical context level DFD to Level-0
  DFD

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DFD EXAMPLE

• We are going to develop a system to record orders
  for pizza.
• When customers call the store, they are asked
  their phone number.
• When the number is typed in inot a compute, the
  name, address, and last order data is
  automatically brought up on the screen.
• If the customer is new, they he is added to the
  system.
• Once the order is take, the total, including tax
  and delivery is calcualted.
• Then the order is given to the cook.
• A receipt is printed.
• Occasionally, coupons are printed so the customer
  can get a discount.
• Drivers who make deliverables give customers a
  copy of the receipt an and a coupon (if any).
• Weekley totals are kept for comparison with last
  years performance

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CONTEXT-LEVEL DFD
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LEVEL-0 DFD