1.Thaat comes from the Twelve Swars of the Saptak.
2.It is compulsory for a Thaat to be Sampoorna ie it should have Seven Sur and they hould be in order.
3.There is no compulsion for Aarohan -Avrohan or variation in Thaat.
4.The formation of Swarmalika in Thaat and similarlity of above mentioned rules in Thaat gives it a name of any famous Raag.
Thaat can never be said as Raag.