Work is starting on a tool for converting WS-CDL (.cdm) based choreographies into BPMN2 choreography models.
One of the areas that needs to be addressed is dealing with sub-choreographies. In the .cdm model, the sub-choreographies are defined in a hierarchy within the same file. The CDM editor enables the user to move between the root choreography, and any of the sub-choreographies (whatever level of nesting) but selecting it from a dropdown menu.
Although BPMN2 as a standard supports having multiple diagrams within the same file, the current Eclipse.org BPMN2 modeller does not support this.
Therefore the proposal is that the separate root and sub-choreographies will be generated as separate BPMN2 choreography files, where 'calling' choreographies will include an appropriate import component to reference the sub-choreography (and file).