There are two general strategies to interact with web services, known as synchronous and asynchronous interactions. In synchronous interactions, both parties communicate in real time (for example, face-to-face conversations, telephone calls, and so on). Both parties maintain the connection intact until the communication is over. In contrast, in asynchronous interactions, both parties communicate outside of real time (for example, e-mails and postal mails). The client establishes a connection with the server, sends the request message, and closes the connection. Then the server of the request message processes the incoming message, generates a response message, establishes a connection with the requesting-party, and sends the response message.

In this section, we realize a common use case where asynchronous invocations play a vital role to achieve the business goal. Let's try to understand the following sample BPEL process and then we will move into the...