Stepwise Refinement

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Stepwise Refinement

• A program design strategy where a solution is
  first described in terms of high level functions,
  then each function is broken down into details
  that are refined in successive steps until the
  whole program is fully defined.
• This PPT originated with Dr. Roland Untch.

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Harvest Task
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• Stepwise Refinement helps us write good
  programs
• Stepwise Refinement tells us not to delve into
  details too quickly, but to gradually solve the
  problem by breaking it into smaller sub-problems.
• Each sub-problem is then solved (also using
  stepwise refinement.)
• Eventually our solutions are expressed in
  detailed terms.

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Harvest Task Design 1
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Other Harvest Task Designs
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Which harvest design is better? Can you think
of other designs?
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We might solve the harvest problem as
follows include ltkarel.hgt int main()
TurnOn() Move() HarvestARow()
TurnLeft() Move() TurnLeft()
HarvestARow() TurnRight() Move()
TurnRight() HarvestARow() // can you
finish the coding??? // more code goes here..
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What are the new commands that you used in your
design?? The command HarvestARow() is a new
command, so the next step is to write this
command. We might write the first new command
as void HarvestARow() PickBeeper()
Move() PickBeeper() Move()
PickBeeper() Move()
PickBeeper() Move()
PickBeeper()
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What other new commands (to Karel) did you use?
We need to write those as well?
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Stepwise Refinement(another definition)

• The software design technique that aims to
  describe functionality at a very high level, then
  partition it repeatedly into more detailed levels
  (one level at a time) until the detail is
  sufficiently refined to express directly as code.
• Also called top-down design.