"Interfaces are better for sharing with the developers who will be responsible for developing the applications consuming your service. ... The service endpoint interface (SEI) is the piece of Java code that is shared between a service and the consumers that make requests on it."https://cxf.apache.org/docs/developing-a-service.html
example of SEI: http://www.mkyong.com/webservices/jax-ws/jax-ws-hello-world-example-document-style/ - see step 1
