Negative shipement for Sales Order which is updated

Hello,

I am ravindra nagar wokring as JDE S&D consultant at client site,

2.my queries regarding negative sales order shipment----once sales order is updated and posted than after we have to reverse the same sales order and update inventory what are the possible solutions as I am aware about credit order but any other solution (back end or front end ) if back end what table are need to be modified please if possible mail me document ...

3. once purchase order is vouchered and posted that if we what to reverse it how it is possible from front end or backent what table file need to update...