The modified WSDL for the BPEL process will have to specify the TravelApprovalPT port type, which will now specify an input message only. It will also have to declare the ClientCallbackPT port type, used to return the result to the client (asynchronously, using a callback). This is shown in the following figure:

Let us first modify the TravelApprovalPT port type used for client interaction, which will now define only the input message:

...
<portType name="TravelApprovalPT">
<operation name="TravelApproval">
<input message="tns:TravelRequestMessage" />
</operation>
</portType>
...

Next we define the client callback port type (ClientCallbackPT) with the ClientCallback operation. The response message is TravelResponseMessage. Notice that the WSDL only specifies this port type, which is implemented by the client.

...
<portType name="ClientCallbackPT">
<operation name="ClientCallback">
<input message="aln:TravelResponseMessage" />
</operation>
</portType>
...

We need to modify the partner link type for the interaction with the BPEL process, called the travelLT link type. We have to add the second role, travelServiceCustomer, which characterizes the client to which the BPEL process will perform a callback on the ClientCallbackPT port type. This is done in the WSDL of the BPEL process:

<plnk:partnerLinkType name="travelLT">
<plnk:role name="travelService" portType="tns:TravelApprovalPT" />
<plnk:role name="travelServiceCustomer" portType="tns:ClientCallbackPT" />
</plnk:partnerLinkType>

Finally, we modify the BPEL process definition. Here we first have to modify the client partner link, where we have to specify the second role—the partnerRole. Here, this is travelServiceCustomer, which characterizes the BPEL process client.

 <partnerLinks> <partnerLink name="client" partnerLinkType="trv:travelLT" myRole="travelService" partnerRole="travelServiceCustomer"/> ...

Next, we change the last activity of the BPEL process. We replace the<reply> activity with the<invoke> callback. For the callback, we use the client partner link and invoke the ClientCallback operation on the ClientCallbackPT port type. The message signature has not changed, so we use the same variable as before, TravelResponse.

...
<!-- Make a callback to the client --> <invoke name="SendResponse" partnerLink="client" portType="trv:ClientCallbackPT" operation="ClientCallback" inputVariable="TravelResponse" />
</sequence>
</process>

Our BPEL process is now asynchronous!

To execute a BPEL process, we need a runtime environment. In Chapter 1 we provided an overview of BPEL servers. Later chapters give a detailed description of the Oracle SOA Suite.