Section 4.5 and 4.6
Relates to comments above.
4.5 The relationship construct allows the definition of the observable 
behavior that two collaborating participants are mutually agreeing to 
exhibit.
4.6 A Channel Type facilitates the collaboration between two Participants.
The channelType construct defines a collaboration point, used for 
communication and synchronization between participants.
The element reference MAY be used for identifying the WSDL service 
reference type of a participant. The service type of a participant is 
distinguished by a set of Token types as specified by the token element 
within the reference element.
The optional element identity MAY be used for identifying an instance of 
a business process implementing a participants role and for identifying 
a logical conversation (group of related message exchanges) between 
participants within a Choreography. The business process type within a 
participant and the different conversations between participants are 
distinguished by a set of Token types as specified by the token element 
within the identity element.

In above: The relationship is to roles not the participants.