Maida and Atta

We Keralites are familiar with Maida, the main ingredient of porotta. What is the difference between Maida and Atta?
Both Maida and Atta flour are made from wheat. The only difference is Atta is whole wheat flour and Maida is refined and finely-milled product of wheat. Maida is extracted from the inner white portion of the wheat after the outer brownish layer is removed.