Ivan Lanese

SCC: a service centered calculus

We seek for a small set of primitives that might serve as a basis for formalising and programming service oriented applications over global computers. As an outcome of this study we introduce here SCC, a process calculus that features explicit notions of service definition, service invocation and session handling. Our proposal has been influenced by Orc, a programming model for structured orchestration of services, but the SCCs session handling mechanism allows for the definition of structured interaction protocols, more complex than the basic request-response provided by Orc. We present syntax and operational semantics of SCC and a number of simple but nontrivial programming examples that demonstrate flexibility of the chosen set of primitives. A few encodings are also provided to relate our proposal with existing ones.

Disciplining Orchestration and Conversation in Service-Oriented Computing

We give a formal account of a calculus for modeling service-based systems, suitable to describe both service composition (orchestration) and the protocol that services run when invoked (conversation). The calculus includes primitives for defining and invoking services, for isolating conversations between clients and servers, and for orchestrating services. The calculus is equipped with a reduction and a labeled transition semantics related by an equivalence result. To hint how the structuring mechanisms of the language can be exploited for static analysis we present a simple type system guaranteeing the compatibility between client and server protocols, an application of bisimilarity to prove equivalence among services, and we discuss deadlock-avoidance.

Reversing higher-order pi

The notion of reversible computation is attracting increasing interest because of its applications in diverse fields, in particular the study of programming abstractions for reliable systems. In this paper, we continue the study undertaken by Danos and Krivine on reversible CCS by defining a reversible higher-order π-calculus (HOπ). We prove that reversibility in our calculus is causally consistent and that one can encode faithfully reversible HOπ into a variant of HOπ.

Bridging the Gap between Interaction- and Process-Oriented Choreographies

In service oriented computing, choreography languages are used to specify multi-party service compositions. Two main approaches have been followed: the interaction-oriented approach of WS-CDL and the process-oriented approach of BPEL4Chor. We investigate the relationship between them. In particular, we consider several interpretations for interaction-oriented choreographies spanning from synchronous to asynchronous communication. Under each of these interpretations we characterize the class of interaction-oriented choreographies which have a process-oriented counterpart, and we formalize the notion of equivalence between the initial interaction-oriented choreography and the corresponding process-oriented one.

A basic algebra of stateless connectors

The conceptual separation between computation and coordination in distributed computing systems motivates the use of peculiar entities commonly called connectors, whose task is managing the interaction among distributed components. Different kinds of connectors exist in the literature at different levels of abstraction. We focus on an algebra of connectors that exploits five kinds of basic connectors (plus their duals), namely symmetry, synchronization, mutual exclusion, hiding and inaction. Basic connectors can be composed in series and in parallel. We first define the operational, observational and denotational semantics of connectors, then we show that the observational and denotational semantics coincide and finally we give a complete normal-form axiomatization. The expressiveness of the framework is witnessed by the ability to model all the (stateless) connectors of the architectural design language CommUnity and of the coordination language Reo.

An operational semantics for a calculus for wireless systems

In wireless systems, the communication mechanism combines features of broadcast, synchrony, and asynchrony. We develop an operational semantics for a calculus of wireless systems. We present different Reduction Semantics and a Labelled Transition Semantics and prove correspondence results between them. Finally, we apply CWS to the modelling of the Alternating Bit Protocol, and prove a simple correctness result as an example of the kind of properties that can be formalized in this framework. A major goal of the semantics is to describe the forms of interference among the activities of processes that are peculiar of wireless systems. Such interference occurs when a location is simultaneously reached by two transmissions. The Reduction Semantics differ on how information about the active transmissions is managed. We use the calculus to describe and analyse a few properties of a version of the Alternating Bit Protocol.

Controlling reversibility in higher-order Pi

We present in this paper a fine-grained rollback primitive for the higher-order π-calculus (HOπ), that builds on the reversibility apparatus of reversible HOπ [9]. The definition of a proper semantics for such a primitive is a surprisingly delicate matter because of the potential interferences between concurrent rollbacks. We define in this paper a high-level operational semantics which we prove sound and complete with respect to reversible HOπ backward reduction. We also define a lowerlevel distributed semantics, which is closer to an actual implementation of the rollback primitive, and we prove it to be fully abstract with respect to the high-level semantics.

Multiparty sessions in SOC

Service oriented applications feature interactions among several participants over the network. Mechanisms such as correlation sets and two-party sessions have been proposed in the literature to separate messages sent to different instances of the same service. This paper presents a process calculus featuring dynamically evolving multiparty sessions to model interactions that spread over several participants. The calculus also provides primitives for service definition/invocation and for structured communication in order to highlight the interactions among the different concepts. Several examples from the SOC area show the suitability of our approach.

Synchronised hyperedge replacement as a model for service oriented computing

This tutorial paper describes a framework for modelling several aspects of distributed computing based on Synchronised Hyperedge Replacement (SHR), a graph rewriting formalism. Components are represented as edges and they rewrite themselves by synchronising with neighbour components the productions that specify their behaviour. The SHR framework has been equipped with many formal devices for representing complex synchronisation mechanisms which can tackle mobility, heterogeneous synchronisations and non-functional aspects, key factors of Service Oriented Computing (SOC). We revise the SHR family as a suitable model for contributing to the formalisation of SOC systems.

On the expressiveness and decidability of higher-order process calculi

In higher-order process calculi the values exchanged in communications may contain processes. A core calculus of higher-order concurrency is studied; it has only the operators necessary to express higher-order communications: input prefix, process output, and parallel composition. By exhibiting a nearly deterministic encoding of Minsky machines, the calculus is shown to be Turing complete and therefore its termination problem is undecidable. Strong bisimilarity, however, is shown to be decidable. Further, the main forms of strong bisimilarity for higher-order processes (higher-order bisimilarity, context bisimilarity, normal bisimilarity, barbed congruence) coincide. They also coincide with their asynchronous versions. A sound and complete axiomatization of bisimilarity is given. Finally, bisimilarity is shown to become undecidable if at least four static (i.e., top-level) restrictions are added to the calculus.