BPEL also supports parallel service invocation. In our example, we have invoked Bookstore A and Bookstore B sequentially. This way, we need to wait for the response from the first service and then for the response from the second service. If these services take longer to execute, the response times will be added together. If we invoke both services in parallel, we only need to wait for the duration of the longer-lasting call, as shown in the following screenshot:

To invoke services in parallel, or to perform any other activities in parallel, we can use the <flow> activity. Within the <flow> activity, we can nest an arbitrary number of flows, and all will execute in parallel. Let's try and modify our example so that Bookstore A and B will be invoked in parallel.