How to add an external XSD file to a BPEL project

Create a BPEL Project, then add the external XSD to your bpel project, inside the bpel folder. Open the bpel file in jdeveloper,
Then in the structure window travel to the messages folder.
By default you can see 2 messages one for request and another for response. If you want to use the custom xsd to the request message type.
Edit the request type to map to the external XSD node. Then refresh the strucure window.
Sometimes the structure window won't get refreshed, in that case you can relaunch the bpel process. This will load the current messages to the structure window.

Messages can be mapped to a element or type based on the struture of the XSDs.
If the node that you are mapping to the message type is element map it as element or if it is type ie.., complex type,
map it as message type otherwise there will be type mismatch and compilation error will be thrown. Once you done mapping to the custom xsd, you can check that in the
structure window.