Abstract. Communication is becoming one of the central elements in software development. As a potential typed foundation for structured communication-based programming, session types have been studied over the last decade for a wide range of process calculi and programming languages, focussing on binary (twoparty) sessions. This work extends the foregoing theories of binary session types to multiparty, asynchronous sessions, which often arise in practical communicationcentred applications. Presented as a typed calculus for mobile processes, the theory introduces a new notion of types in which interactions involving multiple peers are directly abstracted as a global scenario. Global types retain a friendly type syntax of binary session types while capturing complex causal chains of multiparty asynchronous interactions. A global type plays the role of a shared agreement among communication peers, and is used as a basis of efficient type checking through its projection onto individual peers. The fundamental properties of the session type discipline such as communication safety and progress are

Contracts are behavioral descriptions of Web services. We devise a theory of contracts that formalizes the compatibility of a client to a service, and the safe replacement of a service with another service. The use of contracts statically ensures the successful completion of every possible interaction between compatible clients and services. The technical device that underlies the theory is the filter, which is an explicit coercion preventing some possible behaviors of services and, in doing so, make services compatible with different usage scenarios. We show that filters can be seen as proofs of a sound and complete subcontracting deduction system which simultaneously refines and extends Hennessy’s classical axiomatization of the must testing preorder. The relation is decidable and the decision algorithm is obtained via a cut-elimination process that proves the coherence of subcontracting as a logical system. Despite the richness of the technical development, the resulting approach is based on simple ideas and basic intuitions. Remarkably, its application is mostly independent of the language used to program the services or the clients. We outline the practical aspects of our theory by studying two different concrete syntaxes for contracts and applying each of them to Web services languages. We also explore implementation issues of filters and discuss the perspectives of future research

Abstract. A multiparty session forms a unit of structured interactions among many participants which follow a prescribed scenario specified as a global type signature. This paper develops, besides a more traditional communication type system, a novel static interaction type system for global progress in dynamically interleaved multiparty sessions. 1

Abstract. We generalise a theory of multiparty session types for the π-calculus through asynchronous communication subtyping, which allows partial commutativity of actions with maximal flexibility and safe optimisation in message choreography. A sound and complete algorithm for the subtyping relation, which can calculate conformance of optimised end-point processes to an agreed global specification, is presented. As a complementing result, we show a type inference algorithm for deriving the principal global specification from end-point processes which is minimal with respect to subtyping. The resulting theory allows a programmer to choose between a top-down and a bottom-up style of communication programming, ensuring the same desirable properties of typable processes. 1

Abstract. Theories identifying well-formed systems of processes—those that lack communication errors and enjoy strong properties such as deadlock freedom— are based either on session types, which are inhabited by channels, or on contracts, which are inhabited by processes. Current session type theories impose overly restrictive disciplines while contract theories only work for networks with fixed topology. Here we fill the gap between the two approaches by defining a theory of contracts for so-called mobile processes, those whose communications may include delegations and channel references. 1

Abstract. We illustrate the concepts of sessions and session types as they have been developed in the setting of the π-calculus. Motivated by the goal of obtaining a formalisation closer to existing standards and aiming at their enhancement and strengthening, several extensions of the original core system have been proposed, which we survey together with the embodying of sessions into functional and object-oriented languages, as well as some implementations.

Abstract. A fundamental promise of service oriented architecture (SOA) lies in the ease of integrating sharable information, processes, and other resources through interactions among the shared components that are modeled as web services. It is expected that not only the participating services are complex and have observable states, but the number of interacting services may be also large. Prior work on choreographies (conversation protocols) all focuses on specifying how the interacting web services should behave globally. Studies have shown that the relationships between global and local specifications of service interactions could be rather intricate. In this paper, we formulate a framework consisting of logical and implementation levels. We survey and discuss the technical problems and known results concerning service design, analysis and verification in this framework. 1

Abstract. Web services are distributed software components, that are decoupled from each other using interfaces with specified functional behaviors. However, such behavioral specifications are insufficient to demonstrate compliance with certain temporal non-functional policies. An example is demonstrating that a patient’s health-related query sent to a health care service is answered only by a doctor (and not by a secretary). Demonstrating compliance with such policies is important for satisfying governmental privacy regulations. It is often necessary to expose the internals of the web service implementation for demonstrating such compliance, which may compromise modularity. In this work, we provide a language design that enables such demonstrations, while hiding majority of the service’s source code. The key idea is to use greybox specifications to allow service providers to selectively hide and expose parts of their implementation. The overall problem of showing compliance is then reduced to two subproblems: whether the desired properties are satisfied by the service’s greybox specification, and whether this greybox specification is satisfied by the service’s implementation. We specify policies using LTL and solve the first problem by model checking. We solve the second problem by refinement techniques. 1

Choreography conformance and contract compliance have been widely studied in the context of synchronous communication. In this paper we approach a more realistic scenario in which the messages containing the invocations are queued in the called service. More precisely, we study the foundational aspects of contract compliance in a language independent way by just taking contracts to be finite labeled transition systems. Then, we relate the proposed theory of contract compliance with choreography specifications à la WS-CDL where activities are interpreted as pairs of send and receive events. An interesting consequence of adopting a language independent representation of contracts is that choreography projection can be defined in structured operational semantics.

Service Oriented Architectures draw heavily on techniques for reusing and assembling off-the-shelf software components. While powerful, this programming practice is not without a cost: the software architect must ensure that the off-the-shelf components interact safely and in ways that conform with the specification. We develop a new theory for adaptable service compositions. The theory provides an effective framework for analyzing the conformance of contract-based service compositions, and for enforcing their compliance, in a uniform, and formally elegant setting. 1.