We present a process-calculus model for expressing and analyzing service-based systems. Our approach addresses central features of the serviceoriented computational model such as distribution, process delegation, communication and context sensitiveness, and loose coupling. Distinguishing aspects of our model are the notion of conversation context, the adoption of a context sensitive, message-passing-based communication, and of a simple yet expressive mechanism for handling exceptional behavior. We instantiate our model by extending a fragment of the π-calculus, illustrate its expressiveness by means of many examples, and study its basic behavioral theory; in particular, we establish that bisimilarity is a congruence. IntroductionWeb services have emerged mainly as a toolkit of technological and methodological solutions for building open-ended collaborative software systems on the Internet. Many concepts that are frequently put forward as distinctive of service-oriented computing, namely, object-oriented distributed programming, long duration transactions and compensations, separation of workflow from service instances, late binding and discovery of functionalities, are certainly not new, at least when considered in isolation. What is certainly new about services is that they are contributing to physically realize (on the Internet) a global, interaction-based, loosely-coupled, model of computation. We would like to better understand in what sense service orientation is to be seen as a new paradigm to build and reason about distributed systems.The main contributions of this work are the development of a process calculus for service-oriented computing based on a novel notion of conversation context, and the study of its basic behavioral theory. In particular, we establish that bisimilarity is a congruence, thus asserting the proper status of the proposed constructions as operators at the level of the behavioral semantics; we believe that such a result has not yet been provided for other related service calculi. Our starting point is an attempt to isolate and clarify essential characteristics of the service-oriented model, in order to propose a motivation from "first principles" of a reduced set of general abstractions for expressing and analyzing service-based systems. We then instantiate our model by modularly extending the static fragment of the π-calculus with conversation contexts, messagepassing communication primitives, and an exception handling mechanism. Some Key Aspects of Service-Oriented ComputingWe identify as key aspects of the service-oriented computational model: distribution, process delegation, communication and context sensitiveness, and loose coupling.Distribution. The purpose of a service relationship is to allow the incorporation of certain activities in a given system, without having to engage local resources and capabilities to support or implement such activities. By delegating activities to an external service provider, which will perform them using its own remote resources and capabilities,...

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We introduce the concept of behavioral separation as a general principle for disciplining interference in higher-order imperative concurrent programs, and present a type-based approach that systematically develops the concept in the context of an ML-like language extended with concurrency and synchronization primitives. Behavioral separation builds on notions originally introduced for behavioral type systems and separation logics, but shifts the focus from the separation of static program state properties towards the separation of dynamic usage behaviors of runtime values. Behavioral separation types specify how values may be safely used by client code, and can enforce fine-grained interference control disciplines while preserving compositionality, information hiding, and flexibility. We illustrate how our type system, even if based on a small set of general primitives, is already able to tackle fairly challenging program idioms, involving aliasing at various types, concurrency with first-class threads, manipulation of linked data structures, behavioral borrowing, and invariant-based separation.

This paper describes an evolution of the ComponentJ programming language, a component-based Java-like programming language where composition is the chosen structuring mechanism. ComponentJ constructs allow for the high-level specification of component structures, which are the basis for the definition of compound objects. In this paper we present a new language design for ComponentJ which is more flexible and also allows the dynamic reconfiguration of objects. The manipulation of components and composition operations at the programming language level allows for the compile time verification, by a type system, of safety structural properties of ComponentJ programs. This work is based on earlier fundamental results where the main concepts are presented and justified in the form of a core component calculus. .

Abstract. Data-centric multi-user systems, such as web applications, require flexible yet fine-grained data security mechanisms. Such mechanisms are usually enforced by a specially crafted security layer, which adds extra complexity and often leads to error prone coding, easily causing severe security breaches. In this paper, we introduce a programming language approach for enforcing access control policies to data in data-centric programs by static typing. Our development is based on the general concept of refinement type, but extended so as to address realistic and challenging scenarios of permission-based data security, in which policies dynamically depend on the database state, and flexible combinations of column-and row-level protection of data are necessary. We state and prove soundness and safety of our type system, stating that well-typed programs never break the declared data access control policies.

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