Decision Tree Construction: There are different ways to construct trees from data. We will concentrate on the top-down, greedy search approach:
Basic idea:
1. Choose the best attribute a* to place at the root of the tree.
Saperate training set D into subsets {D1, D2.......... , Dk} where each subsets Di containing examples having the same value for a*
Recoursivly apply the algorithm on each new subset untill examples having the same class or there are few of them.
Illustration:
Attributes: Size and Humidity
Size has two values: >t1 or <=t1
Humidity has three values: >t2, (>t3 and <=t2), <=t3
Steps: