The W3C Web Services Choreography Working Group has published the first public working draft of WS Choreography Model Overview. According to the introduction,
Business or other activities that involve multiple different organizations or independent processes that use Web service technology to exchange information can only be successful if they are properly coordinated. This means that the sender and receiver of a message know and agree in advance:
The format and structure of the (SOAP) messages that are exchanged, and
The sequence and conditions in which the messages are exchanged.
WSDL and its extensions provide a mechanism by which the first objective is realized, however, it does not define the sequence and conditions, or choreography, in which messages are exchanged.
To solve this problem, a shared common or "global" definition of the sequence and conditions in which messages are exchanged is produced that describes the observable complementary behavior of all the participants involved. Each participant can then use the definition to build and test solutions that conform to the global definition.
The main advantage of a global definition approach is that it separates the process being followed by an individual business or system within a "domain of control" from the definition of the sequence in which each business or system exchanges information with others. This means that, as long as the "observable" sequence does not change, the rules and logic followed within the domain of control can change at will.
The purpose of this paper is to describe an information model or "meta model" for a Choreography Definition Language that identifies the information and structures required to build a "global" definition.
I don't believe these premises. I think loosely coupled systems with limited if any prior agreements work much better than systems that attempt to legislate what one does with the data one receives. I think any attempt to globallu define behavior is doomed to failure.