Top Down Design

Top-Down Design

• Useful as both a design and an implementation methodology.

• Top-down design is a process in which a large problem is broken down into smaller subproblems and then each of those subproblems is further reduced into its subproblems. This process continues until each subproblem is small. It results in having many easy subproblems.

• Begin with the top-level, user-invoked function, main(), and work toward the lowest level functions that do not call any other functions.

• May proceed depth-first or breadth-first.

  
          1        
          |        
   +------+------+ 
   |      |      | 
   2      3      4 
  / \    /|\     | 
  5 6   7 8 9    10
          |      | 
          11     12
  
  

  • depth-first: 1 2 5 6 3 7 8 11 9 4 10 12
  • breadth-first: 1 2 3 4 5 6 7 8 9 10 11 12

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

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