Types and deadlock freedom in a calculus of services, sessions and pipelines

The notion of a session is fundamental in service-oriented applications, as it serves to separate interactions between clients and different instances of the same service, and to group together logical units of work. Recently, the Service Centered Calculus (SCC) has been proposed as a process calculus designed around the concept of a dyadic session between a service side and an invoker side, where interaction protocols and service orchestration can be conveniently expressed. In this paper we propose a generic type system to collect services' behaviours and then we fix a class of well-typed processes that are guaranteed to be deadlock free, in the sense that they either diverge by invoking new service instances or reach a normal form. The type system is based on previous research on traditional mobile calculi, here conveniently extended and simplified thanks to the neat discipline imposed by the linguistic primitives of SCC.