Microsoft decision tree

Hi again ....i'm trying to understand the works of microsoft decision tree algorithm

I have an example case below :

Customer Id

Debt Level

Income Level

Employment Type

Credit Risk

1

High

High

Self-Employed

Bad

2

High

High

Salaried

Bad

3

High

Low

Salaried

Bad

4

Low

Low

Salaried

Good

5

Low

Low

Self-Emplyed

Bad

6

Low

High

Self-Employed

Good

7

Low

High

Salaried

Good

My question is how about the equations used to determine a split?

Please explain me detailed.

Thanks a lot.

This article explains how the Microsoft Decision Tree algorithm works at a high level and also points to the relevant research papers that the implementation is based on:http://msdn2.microsoft.com/en-us/library/ms175312(SQL.90,d=ide).aspx