Behavioral theory for session-oriented calculi

This chapter presents the behavioral theory of some of the Sensoria core calculi. We consider SSCC, μ se and CC as representatives of the session-based approach and COWS as representative of the correlation-based one. For SSCC, μ se and CC the main point is the structure that the session/conversation mechanism creates in programs. We show how the differences between binary sessions, multiparty sessions and dynamic conversations are captured by different behavioral laws. We also exploit those laws for proving the correctness of program transformations. For COWS the main point is that communication is prioritized (the best matching input captures the output), and this has a strong influence on the behavioral theory of COWS. In particular, we show that communication in COWS is neither purely synchronous nor purely asynchronous

Predicting global usages of resources endowed with local policies

The effective usages of computational resources are a primary concern of up-to-date distributed applications. In this paper, we present a methodology to reason about resource usages (acquisition, release, revision, ...), and therefore the proposed approach enables to predict bad usages of resources. Keeping in mind the interplay between local and global information occurring in the application-resource interactions, we model resources as entities with local policies and global properties governing the overall interactions. Formally, our model takes the shape of an extension of pi-calculus with primitives to manage resources. We develop a Control Flow Analysis computing a static approximation of process behaviour and therefore of the resource usages.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Modelling and Simulation of Asynchronous Real-Time Systems using Timed Rebeca

In this paper we propose an extension of the Rebeca language that can be used to model distributed and asynchronous systems with timing constraints. We provide the formal semantics of the language using Structural Operational Semantics, and show its expressiveness by means of examples. We developed a tool for automated translation from timed Rebeca to the Erlang language, which provides a first implementation of timed Rebeca. We can use the tool to set the parameters of timed Rebeca models, which represent the environment and component variables, and use McErlang to run multiple simulations for different settings. Timed Rebeca restricts the modeller to a pure asynchronous actor-based paradigm, where the structure of the model represents the service oriented architecture, while the computational model matches the network infrastructure. Simulation is shown to be an effective analysis support, specially where model checking faces almost immediate state explosion in an asynchronous setting.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Decoupled execution of synchronous coordination models via behavioural automata

Synchronous coordination systems allow the exchange of data by logically indivisible actions involving all coordinated entities. This paper introduces behavioural automata, a logically synchronous coordination model based on the Reo coordination language, which focuses on relevant aspects for the concurrent evolution of these systems. We show how our automata model encodes the Reo and Linda coordination models and how it introduces an explicit predicate that captures the concurrent evolution, distinguishing local from global actions, and lifting the need of most synchronous models to involve all entities at each coordination step, paving the way to more scalable implementations.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Tipificacao de objectos concorrentes nao uniformes

Concurrent objects can offer services non-uniformly, according to synchronisation constraints, that is, the availability of a service depends on the internal state of the object. Interfaces as types is an approach not suitable to model non uniform service availability, and the message not understood communication error is very restrictive. Hence, we propose a looser definition of communication error by demanding only that messages requesting a method not enabled, but that may be accepted at some time in the future, do not cause errors. This new notion detects messages that are never accepted, either because the requested method does not exists at all, or because the object is blocked and cannot change its state to accept the request. We formalise non uniform concurrent objects in T y Co, a name passing object calculus, and we ensure program safety (i.e. the absence some dynamic aspects of the behaviour of objects, thus, the approach is centred on behaviours as types. The type system assigns terms of the algebra to the names of processes, and ensures that typable processes are neither locally blocked nor run into communication errorsAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Behavioural Types for a Calculus of Concurrent Objects

We present a new type system for TyCO, a name-passing calculus of concurrent objects. The system captures dynamic aspects of the behaviour of objects, namely non-uniform service availability. The notion of processes without errors is loosened, demanding only weak fairness in the treatment of messages

Proceedings 10th International Workshop on the Foundations of Coordination Languages and Software Architectures

Computation nowadays is becoming inherently concurrent, either because of characteristics of the hardware (with multicore processors becoming omnipresent) or due to the ubiquitous presence of distributed systems (incarnated in the Internet). Computational systems are therefore typically distributed, concurrent, mobile, and often involve composition of heterogeneous components. To specify and reason about such systems and go beyond the functional correctness proofs, e.g., by supporting reusability and improving maintainability, approaches such as coordination languages and software architecture are recognised as fundamental. The goal of the this workshop is to put together researchers and practitioners of the aforementioned fields, to share and identify common problems, and to devise general solutions in the context of coordination languages and software architectures.Comment: EPTCS 58, 201

Typing Migration Control in lsdπ

This paper presents a type system to control the migration of code between sites in a concurrent distributed framework. The type system constitutes a decidable mechanism to ensure specific security policies, which control remote communication, process migration, and channel creation. The approach is as follows: each network administrator specifies sites privileges, and a type system checks that the processes running at those sites, as well as the composition of the sites, respect these policies. At runtime, well-typed networks do not violate the security policies declared for each site.