BEA introduces YAS (Yet Another Spec). Usually I dog on specs that WS-Cronies introduce, but I kind of like this one...
This specification describes the WS-CallBack protocol. WS-CallBack is used to dynamically specify where to send asynchronous responses to a SOAP request.
The CallBack header is needed in cases where a web service is using asynchronous communication and the address to which to send responses is not known at deployment time. In order to enable asynchronous responses to requests the requestor must specify in the request where to send the responses. The WS-CallBack protocol provides the SOAP and WSDL 1.1 mechanisms needed to enable this behavior.