In the previous chapters, most of the basic concepts required to implement a very simple BPEL process were explained. We learned how to set up communication channels from BPEL process to external web services (Chapter 1, Hello BPEL). Then, we used those communication channels to invoke those external web services (Chapter 2, Service Invocation). Also we learned how to manipulate data within the BPEL process (Chapter 3, Variables, Data Manipulation, and Expressions).

But the mechanism that we learned to communicate with external web services fails at some point where the external web service takes a nondeterministic time to respond back to the BPEL process. In such scenarios, we can use asynchronous communication channels to invoke external web services.

In this chapter, we will cover the following topics: