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.