Relating two automata-based models of orchestration and choreography

We investigate the relations between two automata-based models for describing and studying distributed services, called contract automata and communicating machines. In the first model, distributed services are abstracted away as automata oblivious of their partners that coordinate with each other through an orchestrator. The second one is concerned with the interactions occurring between distributed services, that are represented by channel-based asynchronous communications; then services are coordinated through choreography. We define a notion of strong agreement on contract automata; exhibit a natural mapping from this model to communicating machines with a synchronous semantics; and give conditions to ensure that strong agreement corresponds to well-formed choreography. Then these results are extended to a more liberal notion of agreement and to a fully asynchronous semantics of communicating machines.