Dear Nicky Khan,
Title of your thread is - How HRA is difined in salary?
In India, HRA is not compulsary except in two or three States there is an Act by which employer is made liable to pay HRA to employees under certain conditions.
HRA is defined on Basic Salary Compenent, certain percentage of it. There is no law as such to pay HRA as stated by our learned member Khaja Vali. Also there is no law which states that you have to pay basic at 40 or 60 percent of CTC.
Though this forum is an open forum in which any member has a right to express his views, my request to members that they should study first before writting any thing and refrain themself to give incorrect picture.