WS-BPEL 2.0 for SOA Composite Applications with Oracle SOA Suite 11g: Define, model, implement, and monitor real-world BPEL business processes with SOA powered BPM.

BPEL uses an XML-based vocabulary that allows us to specify and describe business processes. BPEL is a programming language. Most development environments that support BPEL, such as Oracle JDeveloper, IBM WebSphere Integration Developer, or Eclipse usually provide a visual editor, where we can compose BPEL processes by dragging and dropping the BPEL activities in a visual way. However, the majority of tools also allow a switch to the source view, where you can enter the BPEL code directly. A BPEL visual representation is generated out of BPEL code. In this chapter we will look at the BPEL code.

With BPEL, you can describe business processes in two distinct ways:

A BPEL process consists of steps. Each step is called an activity. BPEL supports basic and structured activities. Basic activities represent basic constructs and are used for common tasks, such as those listed below:

We can then combine these and other basic activities and define complex flows that specify exactly the steps of a business process. To combine basic activities, BPEL supports several structured activities. The most important are:

To demonstrate how business processes are described with BPEL, we will define a simple business process for business travels. Let us consider the business travel process. We describe an oversimplified scenario, where the client invokes the business process, specifying the name of the employee, the destination, the departure date, and the return date. The BPEL business process first checks the employee travel status. We will assume that a service exists through which such a check can be made. Then the BPEL process will check the price for the flight ticket with two airlines American Airlines and Delta Airlines. Again we will suppose that both airline companies provide a service through which such checks can be made. Finally, the BPEL process will select the lower price and return the travel plan to the client.

For the purpose of this example, we first build a synchronous BPEL process, to maintain simplicity. This means that the client will wait for the response...

Our first BPEL business process example was synchronous because this was the easiest case. However, in the real world, we will mostly use asynchronous processes. Most business processes are long running. It makes no sense for a client to wait (and be blocked) for the entire duration of the process. A much better alternative is to model the BPEL process as asynchronous. This means that the client invokes the process, and when the process completes, it performs a callback to the client. This has a few consequences:

Let us now focus on our business process and modify it for asynchronous invocation, presented in the next sequence diagram...

In this chapter, you have become familiar with the basic concepts of service composition with BPEL. BPEL is an XML-based language for business process definition. Each process has a set of activities and interacts with partner services. The BPEL process is also a service.

With BPEL, we can define executable and abstract business processes. In this chapter, we have focused on executable processes. They define exactly the activities of the processes and can be executed on a BPEL-compliant server. We have overviewed the basic concepts of BPEL, described how to invoke services synchronously and asynchronously, and discussed the role of WSDL. BPEL processes can be synchronous or asynchronous and we have overviewed both options. Web Services with which a BPEL process interacts are called partner services. Therefore, we have explained the concepts of partner link types and partner links.

We have overviewed the most important activities for invoking operations, receiving messages, and returning...