SOAP, WSDL, and XSD are the fundamental infrastructure of a SOAP-based web service implementation. WSDL is used to describe the service, and SOAP is the transport layer for sending messages between service consumers and providers.

Services communicate with messages formally defined using XML Schema (XSD). You can think of WSDL as the service’s interface. The implementation is done in Java classes, and communication across the network happens via SOAP. In most cases, consumer would look for a service, get the WSDL for that service, then invoke the service using SOAP.