Individual segments can be deleted from the IDoc before 
dispatch by selecting Functions for the IDoc processing -> 
Settings for filtering in ALE Customizing. The appropriate 
setting depends on the sending and receiving logical R/3 
System.

nothing but deleting the segments

I Doc filtering is nothing but wipout unwnted idoc's that 
ar not required to recevingpartner.

Let us suppose some message type iam sending from my 
central datbase sever to 5 no's application severs let it 
take as some plants in my company code .

The master idoc will contains the data pertaining to the 
five plants.

in thia case for plant No1 date is not reqiured pertaining 
to all the remaining plants i.e 2 3 4 5.

in this case while creting the distribution model whe have 
to mention the filter key's

Then when ever the master IDOC passe through ALE service 
layer it will check;s for filter key' values s for a 
receiver and it will wash out's the all the idoc's 
otherthan the values and cretes the communication IDOC.

alwys communication Idoc is the subset of Master Idoc.

basically idoc is data container .i placed some data in 
idoc .iam sending idoc to  2 systems .if u want to place 
some restrictions to that idoc .u can use   filter