In two-way Web services interaction, at each end point of Web service, both the client and server are required. Therefore,an interaction requires two appropriate WSDLs, one at each end point. These two WSDL interfaces must be correlated
in a certain way to make two-way interaction possible. From the perspective of an end point, two-way full duplex Web
services interaction involves both client-initiated service requests and proactive server pushes for event notification