start routine help (ABAP)

Hi,

I have never written a start routine. I would like to exclude some document types from getting into a ODS. can some one tell me how i will exclude them from a data packet (sample code is what i am looking for).

Another question

I would like to include a Z-field, which basically tells the user that an order header is open/partial/ closed. To do this , i have to compare my document no in the orders ODS to a billing ods, to see if a billing number has been created for that particular order number. In that way i will know that the status is closed if billing number is present. Where do i build this logic into??? in the update rules for the Z-object or the start routine??? Do u have to create a infopackage from the billing ODS to do this???? Will be great if someone could throw light on this in detail...sorry for the long post........