Top Down Design and Programming

Top-Down Programming, or
Stepwise Refinement

• Useful as both a design and an implementation methodology.

• begin with the top-level, user-invoked module and work toward the modules that do not call any other modules.

• May proceed depth-first or breadth-first.

  
          1        
          |        
   +------+------+ 
   |      |      | 
   2      3      4 
  / \    /|\     | 
  5 6   8 9 10   11
          |      | 
          12     13
  
  

  • depth-first: 1 2 5 6 3 8 9 12 10 4 11 13
  • breadth-first: 1 2 3 4 5 6 8 9 10 11 12 13

• Program stubs are used for the lowest, unimplemented layer.

• Problem: will we be able to realize the lowest level modules?

• Advantage: design from the requirements to the details keeps the requirements in focus.