BPMN 2.0 Choreography Language: Interface or Business Contract?

Choreography diagrams have been introduced in the Business Process Model and Notation language 2.0 (BPMN 2.0), one among the most used languages for modelling and analyzing business processes in industry, in order to provide a view on the interaction between participants. Besides the intuitive definition of choreographies as interfaces among participants, the BPMN 2.0 specifications also define choreographies as business contracts among the parties. However, the adoption and the diffusion of the business contract nature of choreography diagrams seem to be hindered by the underspecification of the notation, which does not allow to model and formalize constraints and relationships among choreography entities, which would need to be specified in a business contract. In this paper we provide a preliminary investigation of some of the open issues characterizing BPMN 2.0 choreography diagrams when looking at the business contract nature of the notation, by focusing on those related to messages and participants.