SWO1 - Doubt

hi,

In tcode SWO1 if i take BUS2012(Purchase Order) then it has got few events like change,release,rejection.BUt it shares a same program.My question is when i use this object in Workflows creation how does system interpret that change PO is trigerred or release PO is trigerred.Actually there exist a separate entity for every event but how does system determine whether change or release PO is trigerred.

If i can find its answer then i could be able to introduce a new event for creation as well which is my requirement.

Thanks,

Gaurav