Web Service Choreography (WS-Choreography) is a specification by the W3C defining a XML-based business process modeling language that describes collaboration protocols of cooperating Web Service participants, in which services act as peers, and interactions may be long-lived,The Web Services specifications offer a communication bridge between the heterogeneous computational environments used to develop and host applications. The future of E-Business applications requires the ability to perform long-lived, peer-to-peer collaborations between the participating services, within or across the trusted domains of an organization.

read this also
http://w3TR/ws-cdl-10/
http://w3TR/ws-chor-model/
http://w3TR/ws-cdl-10-primer/
http://en.wikipediawiki/Web_Service_Choreography