there two types of filters 1. single input filter 
2.multiple input filter

connecting the report for 2 databases we use multiple input 
filter. 
for example your report need two database for geting data u 
have to use multiple  input filter.
base class for this filter is
AC single inputfilter
AC multiple input filter
i will give example for in your database u have abc,xyz two 
databases you need data from these two databases so u have 
use multiple filter. normally single input filter we do not 
use.