In the previous sections, we discussed different types of faults that can be generated. They can be explicitly generated by the BPEL developer or implicitly generated by the BPEL runtime. Also, we mentioned that there can be faults generated due to faults in external web service invocations. And in Chapter 5, Interaction Patterns in BPEL, we discussed the synchronous and asynchronous web service invocations. Both of these can generate faults in the BPEL process. But WSDL faults are a special scenario that occurs only due to synchronous web service invocations.

These faults become a special scenario, as the WSDL specification itself defines a WSDL fault for a synchronous web service invocation. So the BPEL runtime implicitly signals faults if it receives something like an incoming fault message rather than defining a <throw> activity explicitly to monitor such incoming fault messages and signals.