You can specify an assertion condition in BPEL versions 1.1 and 2.0 that is executed upon receipt of a callback message in request-response invoke activities, receive activities, reply activities, and onMessage branches of pick and scope activities. The assertion specifies an XPath expression that, when evaluated to false, causes a BPEL fault to be thrown from the activity. This condition provides an alternative to creating a potentially large number of switch, assign, and throw activities after a partner callback.

You can select when to execute a condition:

• Preassert: This condition is executed before the invoke or reply activity send out the outbound message.

• Postassert: This condition is executed after an invoke activity, receive activity, or onMessage branch receives the inbound message.