Hai Nileesha
In case of Mandatory and never we get SystemExceptions depending on the callers Tx.These are consider to be dangerous as it is difficult for the client to recover from system exceptions.But support is riskiest as we cannot determine whether it runs in a transaction or not.
Coming to Not supported we cleary know that it always runs without a tx context irrespective of callers Tx,and u cannot consider suspending of callers transaction as dangerous as it too happens for RequiresNew.And for me running in an unspecified Tx context does not seem to be dangerous.
Though it seems to be little confusing u may get clarified when u read it twice or thrice
srinija
SCJP 1.4,SCWCD 1.4