Classification is a Data Mining (DM) technique used to predict or forecast the unknown information using the historical data. There are many classification techniques. ID3 is a very popular tree based classification algorithm for a categorical data which does not support continuous data. Attribute selection process plays major role in building a classification tree model. Attribute selection in ID3 is based on the information gain. For a continuous attribute there is an extended version of ID3, called C4.5, which uses information gain ratio for discretization.