The first requirement of describing a Raagam is the selection of notes. The present approach is based on the scheme of 'Janaka' and 'Janya' raagams (parent and child). A raagam which uses all the seven notes and has a normal straight (not 'Vakra' -see below) ascent (Aarohanam) and descent (Avarohanam)is a Janaka Raagam (also called Melakartha or Raagaanga Raagam). Others are 'born' out of them. As ri, ga, ma, da, ni can take 2 variations (the black or the white notes on the
keyboard) a simple scheme can provide 32 possible combinations (2 x 2 x 2 x 2 x 2). Actually 72 combinations are now used based on a slightly more complex scheme for the Janaka raagams (Venkatamakhi's Melams - see this page and subsequent pages)the bulk of raagams in use come under the 32.
The Janya raagams as a rule have to use the same variety of the 5 notes
ri, ga ma da ni as in the parent Raagam. As the type of notes of the Janaka Raagam are defined the notes of the Janya get defined. The Janya may omit some of the notes (other than sa) of the Janaka and may also have a devious (winding) or 'Vakra' ascent or descent (such as sa-ga-ri-ga-
ma-pa-da-pa-Sa in Aarohanam - coming down to ri after ga and to pa after da and then going up ). To appreciate how the Janaka-Janya scheme works see and listen (audio at 1 kattai or C Aadaara Sruthi) to the Aarohanam-Avarohanam of the Janaka and Janya for Saaveri (parent Maayaamaalavagowla). Saaveri omits ga and ni in the ascent. Sahaana (parent Harikaambodhi) is an example of Vakra ascent and descent. Hindholam (parent Natabhairavi) has identical ascent and descent omitting ri and pa. Note that in all these cases the variety of ri,ga,ma,da and ni are the same in the Janaka Raagam as in the Janya Raagam. Also listen to few lines of compositions in Saaveri (the sruthi here is about 2.5 kattai or D#) , Sahaana with sruthi 1 kattai (C) and Hindholam (with sruthi at 1 kattai - C).
There are exceptions to the rule that the Janaka Raagam should use the same variety of ri,ga,ma,da and ni. The variety not found in the Janaka may occur in some specific phrases of the Janya or in ascent only or descent only. Such Raagams are called Bhaashaanga Raagams, explained later.