In the previous chapter, we learned the basics of BPEL. We learned that BPEL processes can be synchronous or asynchronous. BPEL processes consist of activities. A process usually begins with a <receive> activity, which is responsible for receiving the request from the process client. Then, the BPEL process executes some logic. So far, we have become familiar with the <assign> activity for manipulating variables and with the <if> activity for conditions.

We have also learned that BPEL is a programming-in-the-large language, meaning that we do not program distinct functionalities in BPEL. Rather, we use BPEL to orchestrate services—in other words, it invokes several services in a specific order to perform a certain business process.

In a typical scenario, the BPEL business process receives a request. To fulfill it, the process then invokes the involved services and finally responds to the original caller. Every BPEL process specifies the...