Goal Directed Planning

Definition   GOAL DIRECTED PLANNING is the problem solving strategy of:

1. identifying a goal
   
2. determining the information needed to achieve the goal
   
3. establish as subgoals the problems of securing the information needed to achieve the goal.
   
4. ``recursively'' applying this same method to the problems established as subgoals.
   

Goal directed planning is a ``procedural'' variant of problem decomposition.  

Problem  

Given a congruent figure made up of squares with a collective area that is 187.32 square units determine the perimeter of the figure?   Solving the perimeter problem by means of goal directed planning:

• To determine the perimeter of the figure you need to know the length of the small square side,  and the number of such sides.
  
• To determine the length of the small square side we need to know the area of the square.
  
• To determine the area of one small square we need to know the number of small squares,  and the total area of the figure.
  

Working in a ``bottom-up'' fashion either:

• record an item of information
  
• compute the value
  

• record the total area
  
• record the number of small squares
  
• compute the area of a small square
  
• compute the length of one side
  
• record the number of small sides around the perimeter
  
• compute the perimeter
  

?   class ---- PerimeterApp   ?   Program   / /Compute the perimeter         double totalArea = 187.32;         int nrSquares = 15;         double squareArea = totalArea /nrSquares;         double sideLength = Math.sqrt (squareArea);         int nrExternalSides = 20;         double perimeter = sideLength * nrExternalSides;           / /Display the results         IO.print (``The perimeter is ``);         IO.print (perimeter);         IO.print (``square units.'');         IO.println ();

The Math Class  

Form:   math.sqrt (< double >) -- < double >  

Meaning:   Compute the square root of the perimeter.  

Example:   double value = Math.sqrt (16.0);  

value -- 4  

Form:   Math.PI -- < double >  

Meaning:   Reference the classic greek constant 3.141 ...  

Example:   double r = 5.8;  

double a = r * r * Math.PI;  

Form:   Math.pow (< double >,  < double >) -- < double >  

Meaning:   Raise the first value to the power of the second.  

Example:   Math.pow (3.0,  2)  

value -- 9.0  

Note on Arithmetic

< int > + < int > -- < int >   < double > + < double > -- < double >   < int > + < double > -- < double >

 

Similarly for * - /  

Example:

IO.println (5 / 2) -- 2     IO.println (5.0 / 2.0) -- 2.5