validation means, system can identify any wrong transations 
will post to the system and it will dispy the error which 
we hav post wrongly.

substitution means, some time system automaticaly identify 
wrng enrty and rectify wrong entry system it self.
ex: if we enterd posting date 01.04.2008 but posting period 
we entered as 3rd month, then system automatically change 
tht period in to 1 it self.

plz ignore wen i m wrng, send 
right.....dearchandhu@gmail.com