Towards a Hierarchy of Negative Test Operators for Generative Communication

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On the Expressiveness of Movement in Pure Mobile Ambients

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On the Serializability of Transactions in JavaSpaces

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When to Move to Transfer Nets On the limits of Petri nets as models for process calculi

International audiencePierpaolo Degano has been an influential pioneer in the investigation of Petri nets as models for concurrent process calculi (see e.g. the well-known seminal work by Degano–De Nicola–Montanari also known as DDM88). In this paper, we address the limits of classical Petri nets by discussing when it is necessary to move to the so-called Transfer nets, in which transitions can also move to a target place all the tokens currently present in a source place. More precisely, we consider a simple calculus of processes that interact by generating/consuming messages into/from a shared repository. For this calculus classical Petri nets can faithfully model the process behavior. Then we present a simple extension with a primitive allowing processes to atomically rename all the data of a given kind. We show that with the addition of such primitive it is necessary to move to Transfer nets to obtain a faithful modeling

Adaptable processes

We propose the concept of adaptable processes as a way of overcoming the limitations that process calculi have for describing patterns of dynamic process evolution. Such patterns rely on direct ways of controlling the behavior and location of running processes, and so they are at the heart of the adaptation capabilities present in many modern concurrent systems. Adaptable processes have a location and are sensible to actions of dynamic update at runtime; this allows to express a wide range of evolvability patterns for concurrent processes. We introduce a core calculus of adaptable processes and propose two verification problems for them: bounded and eventual adaptation. While the former ensures that the number of consecutive erroneous states that can be traversed during a computation is bound by some given number k, the latter ensures that if the system enters into a state with errors then a state without errors will be eventually reached. We study the (un)decidability of these two problems in several variants of the calculus, which result from considering dynamic and static topologies of adaptable processes as well as different evolvability patterns. Rather than a specification language, our calculus intends to be a basis for investigating the fundamental properties of evolvable processes and for developing richer languages with evolvability capabilities

Fair Refinement for Asynchronous Session Types

International audienceSession types are widely used as abstractions of asynchronous message passing systems. Refinement for such abstractions is crucial as it allows improvements of a given component without compromising its compatibility with the rest of the system. In the context of session types, the most general notion of refinement is the asynchronous session subtyping, which allows to anticipate message emissions but only under certain conditions. In particular, asynchronous session subtyping rules out candidates subtypes that occur naturally in communication protocols where, e.g., two parties simultaneously send each other a finite but unspecified amount of messages before removing them from their respective buffers. To address this shortcoming, we study fair compliance over asynchronous session types and fair refinement as the relation that preserves it. This allows us to propose a novel variant of session subtyping that leverages the notion of controllability from service contract theory and that is a sound characterisation of fair refinement. In addition, we show that both fair refinement and our novel subtyping are undecidable. We also present a sound algorithm, and its implementation, which deals with examples that feature potentially unbounded buffering

On the Expressiveness of Synchronization in Component Deployment

International audienceThe Aeolus component problem of automatic deployment of complex distributed component systems. In the general setting, the task of checking if a distributed application can be deployed is an undecidable problem. However, the current undecidability proof in Aeolus assumes the possibility to perform in a synchronized way atomic configuration actions on a set of interdependent components: this feature is usually not supported by deployment frameworks. In this paper we prove that even without synchronized configuration actions the Aeolus component model is still Turing complete. On the contrary, we show that other Aeolus features like capacity constraints and conflicts are necessary: if we remove the former the deployment problem becomes non-primitive recursive, while in the latter it becomes poly-time

A Planning Tool Supporting the Deployment of Cloud Applications

Other publicationCloud computing offers the possibility to build sophisticated software systems on virtualized infrastructures at a fraction of the cost necessary just a few years ago. Nevertheless, the deployment of such complex systems is a serious issue due to the large number of involved software packages and services, and to their elaborated interdependencies. In this paper we address the challenge of automatizing this complex deployment process. We first formalize it as a planning problem and observe that standard planning tools can effectively solve it only on small and trivial instances. For this reason, we propose an ad hoc planning technique which we validate by means of a prototype implementation able to effectively solve this deployment problem also on instances of realistic size