Hi Sreenivas,
SAP_WAPI_DECISION_COMPLETE will work for any User Decision task - even most custom ones.
For other business objects and class methods, you generally need some sort of specific approval BAPI or equivalent to be provided by the application, which will make the approval changes in the application itself, as if the user had manually launched the application. Many applications provide such options, quite a lot don't and you might need to take a slightly different approach.
Depending on how that application works, and whether the approval BAPI or equivalent raises an event such as <object>.APPROVED or <object>.REJECTED you can either use those as terminating events of your workflow task, or use SAP_WAPI_WORKITEM_COMPLETE to close the work item.
If you have a specific BOR object or ABAP Class you want to approve you need to ask that as a separate question, as different people work in different applications and will be able to advise what works best for the application in question.
Hope that helps
Rgds,
Jocelyn
