how can i rollback the tasks done by webservice?

Hi,

I am implementing a webservice.

Which posts data in a DB as well as SAP.

posting data into DB has to be implemented by calling ejb.

posting data into SAP has to be implemented by calling XI webservice.

For this i am assuming like this way...............

Call the ejb to post data into DB.

Call the XI webservice to post data into SAP.

If XI webservice is executed properly then commit the transaction to post data into DB.

But there may be another possibility ...........

While commiting the transaction if any exception comes ,

How can i rollback the XI webservice?Is it possible to rollback the webservice

after it is executed?

Can any one guide me.

Regards

Madhu