arXiv subjects

Emilio Tuosto

Publications and source records attributed to Emilio Tuosto.

At least 37 records · Page 2Linked to original sources

arXiv2020

An Abstract Framework for Choreographic Testing

We initiate the development of a model-driven testing framework for message-passing systems. The notion of test for communicating systems cannot simply be borrowed from existing proposals. Therefore, we formalize a notion of suitable distributed tests for a given choreography and devise an algorithm that generates tests as projections of global views. Our algorithm abstracts away from the actual projection operation, for which we only set basic requirements. The algorithm can be instantiated by reusing existing projection operations (designed to generate local implementations of global models) as they satisfy our requirements. Finally, we show the correctness of the approach and validate our methodology via an illustrative example.

cs.FL↗

arXiv2020

Towards Refinable Choreographies

We investigate refinement in the context of choreographies. We introduce refinable global choreographies allowing for the underspecification of protocols, whose interactions can be refined into actual protocols. Arbitrary refinements may spoil well-formedness, that is the sufficient conditions that guarantee a protocol to be implementable. We introduce a typing discipline that enforces well-formedness of typed choreographies. Then we unveil the relation among refinable choregraphies and their admissible refinements in terms of an axiom scheme.

cs.LO↗

arXiv2020

Probabilistic Analysis of Binary Sessions

We study a probabilistic variant of binary session types that relate to a class of Finite-State Markov Chains. The probability annotations in session types enable the reasoning on the probability that a session terminates successfully, for some user-definable notion of successful termination. We develop a type system for a simple session calculus featuring probabilistic choices and show that the success probability of well-typed processes agrees with that of the sessions they use. To this aim, the type system needs to track the propagation of probabilistic choices across different sessions.

cs.LO↗

arXiv2019

Interface Automata for Choreographies

Choreographic approaches to message-passing applications can be regarded as an instance of the model-driven development principles. Choreographies specify interactions among distributed participants coordinating among themselves with message-passing at two levels of abstractions. A global view of the application is specified with a model that abstracts away from asynchrony while a local view of the application specifies the communication pattern of each participant. Noteworthy, the latter view can typically be algorithmically obtained by projection of the global view. A crucial element of this approach is to verify the so-called well-formed conditions on global views so that its projections realise a sound communication protocol. We introduce a novel local model, group interface automata, to represent the local view of choreographies and propose a new method to verify the well-formedness of global choreographies. We rely on a recently proposed semantics of global views formalised in terms of pomsets.

cs.FL↗

arXiv2019

On Learning Nominal Automata with Binders

We investigate a learning algorithm in the context of nominal automata, an extension of classical automata to alphabets featuring names. This class of automata captures nominal regular languages; analogously to the classical language theory, nominal automata have been shown to characterise nominal regular expressions with binders. These formalisms are amenable to abstract modelling resource-aware computations. We propose a learning algorithm on nominal regular languages with binders. Our algorithm generalises Angluin's L* algorithm with respect to nominal regular languages with binders. We show the correctness and study the theoretical complexity of our algorithm.

cs.FL↗

arXiv2017

Tool Supported Analysis of IoT

The design of IoT systems could benefit from the combination of two different analyses. We perform a first analysis to approximate how data flow across the system components, while the second analysis checks their communication soundness. We show how the combination of these two analyses yields further benefits hardly achievable by separately using each of them. We exploit two independently developed tools for the analyses. Firstly, we specify IoT systems in IoT-LySa, a simple specification language featuring asynchronous multicast communication of tuples. The values carried by the tuples are drawn from a term-algebra obtained by a parametric signature. The analysis of communication soundness is supported by ChorGram, a tool developed to verify the compatibility of communicating finite-state machines. In order to combine the analyses we implement an encoding of IoT-LySa processes into communicating machines. This encoding is not completely straightforward because IoT-LySa has multicast communications with data, while communication machines are based on point-to-point communications where only finitely many symbols can be exchanged. To highlight the benefits of our approach we appeal to a simple yet illustrative example.

cs.LO↗

arXiv2017

Reliability and Fault-Tolerance by Choreographic Design

Distributed programs are hard to get right because they are required to be open, scalable, long-running, and tolerant to faults. In particular, the recent approaches to distributed software based on (micro-)services where different services are developed independently by disparate teams exacerbate the problem. In fact, services are meant to be composed together and run in open context where unpredictable behaviours can emerge. This makes it necessary to adopt suitable strategies for monitoring the execution and incorporate recovery and adaptation mechanisms so to make distributed programs more flexible and robust. The typical approach that is currently adopted is to embed such mechanisms in the program logic, which makes it hard to extract, compare and debug. We propose an approach that employs formal abstractions for specifying failure recovery and adaptation strategies. Although implementation agnostic, these abstractions would be amenable to algorithmic synthesis of code, monitoring and tests. We consider message-passing programs (a la Erlang, Go, or MPI) that are gaining momentum both in academia and industry. Our research agenda consists of (1) the definition of formal behavioural models encompassing failures, (2) the specification of the relevant properties of adaptation and recovery strategy, (3) the automatic generation of monitoring, recovery, and adaptation logic in target languages of interest.

cs.PL↗

arXiv2017

On Sessions and Infinite Data

We define a novel calculus that combines a call-by-name functional core with session-based communication primitives. We develop a typing discipline that guarantees both normalisation of expressions and progress of processes and that uncovers an unexpected interplay between evaluation and communication.

cs.LO↗

arXiv2017

Choreographies for Automatic Recovery

We propose a choreographic model of reversible computations based on a conservative extension of global graphs and communicating finite-state machines. The main advantage of our approach is that does not require to instrument models in order to control reversibility but for a minor decoration of branches. We show that our models are conservative extensions of existing ones and that the reversible semantics guarantees causal consistency.

cs.LO↗

arXiv2016

Honesty by Typing

We propose a type system for a calculus of contracting processes. Processes can establish sessions by stipulating contracts, and then can interact either by keeping the promises made, or not. Type safety guarantees that a typeable process is honest - that is, it abides by the contracts it has stipulated in all possible contexts, even in presence of dishonest adversaries. Type inference is decidable, and it allows to safely approximate the honesty of processes using either synchronous or asynchronous communication.

cs.PL↗

arXiv2016

An Abstract Semantics of the Global View of Choreographies

We introduce an abstract semantics of the global view of choreographies. Our semantics is given in terms of pre-orders and can accommodate different lower level semantics. We discuss the adequacy of our model by considering its relation with communicating machines, that we use to formalise the local view. Interestingly, our framework seems to be more expressive than others where semantics of global views have been considered. This will be illustrated by discussing some interesting examples.

cs.LO↗

arXiv2016

Communicating machines as a dynamic binding mechanism of services

Distributed software is becoming more and more dynamic to support applications able to respond and adapt to the changes of their execution environment. For instance, service-oriented computing (SOC) envisages applications as services running over globally available computational resources where discovery and binding between them is transparently performed by a middleware. Asynchronous Relational Networks (ARNs) is a well-known formal orchestration model, based on hypergraphs, for the description of service-oriented software artefacts. Choreography and orchestration are the two main design principles for the development of distributed software. In this work, we propose Communicating Relational Networks (CRNs), which is a variant of ARNs, but relies on choreographies for the characterisation of the communicational aspects of a software artefact, and for making their automated analysis more efficient.

cs.LO↗

arXiv2014

From Orchestration to Choreography through Contract Automata

We study the relations between a contract automata and an interaction model. In the former model, distributed services are abstracted away as automata - oblivious of their partners - that coordinate with each other through an orchestrator. The interaction model relies on channel-based asynchronous communication and choreography to coordinate distributed services. We define a notion of strong agreement on the contract model, exhibit a natural mapping from the contract model to the interaction model, and give conditions to ensure that strong agreement corresponds to well-formed choreography.

cs.FL↗

arXiv2013

Nominal Regular Expressions for Languages over Infinite Alphabets. Extended Abstract

We propose regular expressions to abstractly model and study properties of resource-aware computations. Inspired by nominal techniques -- as those popular in process calculi -- we extend classical regular expressions with names (to model computational resources) and suitable operators (for allocation, deallocation, scoping of, and freshness conditions on resources). We discuss classes of such nominal regular expressions, show how such expressions have natural interpretations in terms of languages over infinite alphabets, and give Kleene theorems to characterise their formal languages in terms of nominal automata.

cs.FL↗

arXiv2013

On Recovering from Run-time Misbehaviour in ADR

We propose a monitoring mechanism for recording the evolution of systems after certain computations, maintaining the history in a tree-like structure. Technically, we develop the monitoring mechanism in a variant of ADR (after Architectural Design Rewriting), a rule-based formal framework for modelling the evolution of architectures of systems. The hierarchical nature of ADR allows us to take full advantage of the tree-like structure of the monitoring mechanism. We exploit this mechanism to formally define new rewriting mechanisms for ADR reconfiguration rules. Also, by monitoring the evolution we propose a way of identifying which part of a system has been affected when unexpected run-time behaviours emerge. Moreover, we propose a methodology to suggest reconfigurations that could potentially lead the system in a non-erroneous state.

cs.SE↗

arXiv2012

Enforcing Architectural Styles in Presence of Unexpected Distributed Reconfigurations

Architectural Design Rewriting (ADR, for short) is a rule-based formal framework for modelling the evolution of architectures of distributed systems. Rules allow ADR graphs to be refined. After equipping ADR with a simple logic, we equip rules with pre- and post-conditions; the former constraints the applicability of the rules while the later specifies properties of the resulting graphs. We give an algorithm to compute the weakest pre-condition out of a rule and its post-condition. On top of this algorithm, we design a simple methodology that allows us to select which rules can be applied at the architectural level to reconfigure a system so to regain its architectural style when it becomes compromised by unexpected run-time reconfigurations.

cs.LO↗

arXiv2012

Synthesising Choreographies from Local Session Types (extended version)

Designing and analysing multiparty distributed interactions can be achieved either by means of a global view (e.g. in choreography-based approaches) or by composing available computational entities (e.g. in service orchestration). This paper proposes a typing systems which allows, under some conditions, to synthesise a choreography (i.e. a multiparty global type) from a set of local session types which describe end-point behaviours (i.e. local types).

cs.PL↗

arXiv2012

On the realizability of contracts in dishonest systems

We develop a theory of contracting systems, where behavioural contracts may be violated by dishonest participants after they have been agreed upon - unlike in traditional approaches based on behavioural types. We consider the contracts of \cite{CastagnaPadovaniGesbert09toplas}, and we embed them in a calculus that allows distributed participants to advertise contracts, reach agreements, query the fulfilment of contracts, and realise them (or choose not to). Our contract theory makes explicit who is culpable at each step of a computation. A participant is honest in a given context S when she is not culpable in each possible interaction with S. Our main result is a sufficient criterion for classifying a participant as honest in all possible contexts.

cs.PL↗