Section: New Results

Service-oriented computing

Participants : Mario Bravetti, Ivan Lanese, Fabrizio Montesi, Gianluigi Zavattaro.

Primitives

We have studied primitives used in the context of service-oriented computing, at different levels of abstraction and in different contexts. At the abstract level, we considered both standard web services and Internet of Things, where computational and communication capabilities are attached to real-world objects such as smartphones or alarm clocks. For web services, we defined SSCC (Stream-based Service-Centered Calculus) [17] , a calculus allowing to describe both service composition (orchestration) via streams and the protocols that services follow when invoked (conversation). We assessed the expressive power of SSCC by modeling van der Aalst's workflow patterns and an automotive case study from the European project Sensoria. For analysis, we presented a simple type system ensuring compatibility of client and service protocols. We also studied the behavioral theory of the calculus, highlighting some axioms that capture the behavior of the different primitives. As a final application of the theory, we defined and proved correct some program transformations. For Internet of Things, a main contribution [37] has been the definition of a calculus and of an equivalence allowing to capture the behavior of the system as seen by the human end-user. Since this equivalence is not compositional we defined also a finer equivalence which is compositional. We showed how our equivalences can be applied to reason on simple Internet of Things examples.

At a more concrete level, we have continued to study and extend the Jolie language. In [44] we present a detailed description of the Jolie language. We put our emphasis on how Jolie can deal with heterogeneous services. On the one hand, Jolie combines computation and composition primitives in an intuitive and concise syntax. On the other hand, the behavior and deployment of a Jolie program are orthogonal: they can be independently defined and recombined as long as they have compatible typing. In [42] we extended Jolie to model process-aware web information systems. Our major contribution is to offer a unifying approach for the programming of distributed architectures based on HTTP that support typical features of the process-oriented paradigm, such as structured communication flows and multiparty sessions.

Choreographies

Choreographies are high-level descriptions of distributed interacting systems featuring as basic unit a communication between two participants. A main feature of choreographies is that they are deadlock-free by construction. From a choreography one can automatically derive the behavior of each participant using a notion of projection. Under suitable conditions on the structure of a choreography, the correctness of its projection can be established in terms of a trace-based semantics. In [24] we have proposed a purely-global programming model. The idea is to define abstract choreographies – called protocol specifications – and use them to type a more concrete choreography. This more concrete choreography is used to generate executable code for the different participants. The approach is based on a novel interpretation of asynchrony and parallelism. We evaluated the approach by providing a prototype implementation for a concrete programming language and by applying it to some examples from multicore and service-oriented programming  [49] . In [43] we tackled one of the main limitations of choreographies, namely the fact that they model closed systems. To this end we proposed a notion of composable choreographies. The key of our approach is the introduction of partial choreographies, which can mix global descriptions with communications among external peers. We prove that if two choreographies are composable, then the endpoints independently generated from each choreography are also composable, preserving their typability and deadlock-freedom. In [39] we showed how to transform choreographies which do not satisfy the conditions for their projection into choreographies that satisfy them preserving their behavior and enabling a correct projection.