Hi Sathya,
It might be a late reply. Anyway, its never too late..
I think you are looking to view carnatic from the western music point of view. Well, its little different though.

Aro and Avaro is the main theory in CArnatic. It clearly says which notes can follow a particular note and which cannot. For example, in Bilahari , which is a beautiful raga, of course, u ascend 's r g p d S' and decend 'S n d p m g r s'. So its very clear that u cannot play 'g m' or 'm p' also 'd n' or 'n S' while u ascend and in the decend, all the notes are included. So u can go as 's r g p m g p' and 'p d S n d' and so on...Its just takes a only little while to get the grasp. but one u get it its very easy concept. So its as simple as that.

First try to familiarize with a pentatonic or raga which has symmetric aro and avaro like mohanam or Hamsadwani and then move to non-sysmmetric aro and avaro...
I hope this helps. U might have figured it out by now..still....my small help...

Regards
Ganesh