51 research outputs found
A compositional coalgebraic model of a fragment of fusion calculus
This work is a further step in exploring the labelled transitions and bisimulations of fusion calculi. We follow the approach developed by Turi and Plotkin for lifting transition systems with a syntactic structure to bialgebras and, thus, we provide a compositional model of the fusion calculus with explicit fusions. In such a model, the bisimilarity relation induced by the unique morphism to the final coalgebra coincides with fusion hyperequivalence and it is a congruence with respect to the operations of the calculus. The key novelty in our work is to give an account of explicit fusions through labelled transitions. In this short essay, we focus on a fragment of the fusion calculus without recursion and replication
Contractual Testing
Variants of must testing approach have been successfully applied in Service Oriented Computing for capturing compliance between (contracts exposed by) a client and a service and for characterising safe replacement, namely
the fact that compliance is preserved when a service exposing a ’smaller’ contract is replaced by another one with a ’larger’ contract. Nevertheless, in multi-party
interactions, partners often lack full coordination capabilities. Such a scenario calls for less discriminating notions of testing in which observers are, e.g., the
description of uncoordinated multiparty contexts or contexts that are unable to observe the complete behaviour of the process under test. In this paper we propose an extended notion of must preorder, called contractual preorder, according to which contracts are compared according to their ability to pass only the tests belonging to a given set. We show the generality of our framework by proving that preorders induced by existing notions of compliance in a distributed setting are instances of the contractual preorder when restricting to suitable sets of observers
A compositional coalgebraic model of a fragment of fusion calculus
This work is a further step in exploring the labelled transitions and bisimulations of fusion calculi. We follow the approach developed by Turi and Plotkin for lifting transition systems with a syntactic structure to bialgebras and, thus, we provide a compositional model of the fusion calculus with explicit fusions. In such a model, the bisimilarity relation induced by the unique morphism to the final coalgebra coincides with fusion hyperequivalence and it is a congruence with respect to the operations of the calculus. The key novelty in our work is to give an account of explicit fusions through labelled transitions. In this short essay, we focus on a fragment of the fusion calculus without recursion and replication
Contracts for Abstract Processes in Service Composition
Contracts are a well-established approach for describing and analyzing
behavioral aspects of web service compositions. The theory of contracts comes
equipped with a notion of compatibility between clients and servers that
ensures that every possible interaction between compatible clients and servers
will complete successfully. It is generally agreed that real applications often
require the ability of exposing just partial descriptions of their behaviors,
which are usually known as abstract processes. We propose a formal
characterization of abstraction as an extension of the usual symbolic
bisimulation and we recover the notion of abstraction in the context of
contracts.Comment: In Proceedings FIT 2010, arXiv:1101.426
Amending Contracts for Choreographies
Distributed interactions can be suitably designed in terms of choreographies.
Such abstractions can be thought of as global descriptions of the coordination
of several distributed parties. Global assertions define contracts for
choreographies by annotating multiparty session types with logical formulae to
validate the content of the exchanged messages. The introduction of such
constraints is a critical design issue as it may be hard to specify contracts
that allow each party to be able to progress without violating the contract. In
this paper, we propose three methods that automatically correct inconsistent
global assertions. The methods are compared by discussing their applicability
and the relationships between the amended global assertions and the original
(inconsistent) ones.Comment: In Proceedings ICE 2011, arXiv:1108.014
Contracts in distributed systems
We present a parametric calculus for contract-based computing in distributed
systems. By abstracting from the actual contract language, our calculus
generalises both the contracts-as-processes and contracts-as-formulae
paradigms. The calculus features primitives for advertising contracts, for
reaching agreements, and for querying the fulfilment of contracts. Coordination
among principals happens via multi-party sessions, which are created once
agreements are reached. We present two instances of our calculus, by modelling
contracts as (i) processes in a variant of CCS, and (ii) as formulae in a
logic. With the help of a few examples, we discuss the primitives of our
calculus, as well as some possible variants.Comment: In Proceedings ICE 2011, arXiv:1108.014
A Fully Abstract Symbolic Semantics for Psi-Calculi
We present a symbolic transition system and bisimulation equivalence for
psi-calculi, and show that it is fully abstract with respect to bisimulation
congruence in the non-symbolic semantics.
A psi-calculus is an extension of the pi-calculus with nominal data types for
data structures and for logical assertions representing facts about data. These
can be transmitted between processes and their names can be statically scoped
using the standard pi-calculus mechanism to allow for scope migrations.
Psi-calculi can be more general than other proposed extensions of the
pi-calculus such as the applied pi-calculus, the spi-calculus, the fusion
calculus, or the concurrent constraint pi-calculus.
Symbolic semantics are necessary for an efficient implementation of the
calculus in automated tools exploring state spaces, and the full abstraction
property means the semantics of a process does not change from the original
The role of immune suppression in COVID-19 hospitalization: clinical and epidemiological trends over three years of SARS-CoV-2 epidemic
Specific immune suppression types have been associated with a greater risk of severe COVID-19 disease and death. We analyzed data from patients >17 years that were hospitalized for COVID-19 at the “Fondazione IRCCS Ca′ Granda Ospedale Maggiore Policlinico” in Milan (Lombardy, Northern Italy). The study included 1727 SARS-CoV-2-positive patients (1,131 males, median age of 65 years) hospitalized between February 2020 and November 2022. Of these, 321 (18.6%, CI: 16.8–20.4%) had at least one condition defining immune suppression. Immune suppressed subjects were more likely to have other co-morbidities (80.4% vs. 69.8%, p < 0.001) and be vaccinated (37% vs. 12.7%, p < 0.001). We evaluated the contribution of immune suppression to hospitalization during the various stages of the epidemic and investigated whether immune suppression contributed to severe outcomes and death, also considering the vaccination status of the patients. The proportion of immune suppressed patients among all hospitalizations (initially stable at <20%) started to increase around December 2021, and remained high (30–50%). This change coincided with an increase in the proportions of older patients and patients with co-morbidities and with a decrease in the proportion of patients with severe outcomes. Vaccinated patients showed a lower proportion of severe outcomes; among non-vaccinated patients, severe outcomes were more common in immune suppressed individuals. Immune suppression was a significant predictor of severe outcomes, after adjusting for age, sex, co-morbidities, period of hospitalization, and vaccination status (OR: 1.64; 95% CI: 1.23–2.19), while vaccination was a protective factor (OR: 0.31; 95% IC: 0.20–0.47). However, after November 2021, differences in disease outcomes between vaccinated and non-vaccinated groups (for both immune suppressed and immune competent subjects) disappeared. Since December 2021, the spread of the less virulent Omicron variant and an overall higher level of induced and/or natural immunity likely contributed to the observed shift in hospitalized patient characteristics. Nonetheless, vaccination against SARS-CoV-2, likely in combination with naturally acquired immunity, effectively reduced severe outcomes in both immune competent (73.9% vs. 48.2%, p < 0.001) and immune suppressed (66.4% vs. 35.2%, p < 0.001) patients, confirming previous observations about the value of the vaccine in preventing serious disease
A Compositional Coalgebraic Model of Monadic Fusion Calculus
We propose a compositional coalgebraic semantics of the Fusion calculus of Parrow and Victor in the version with explicit fusions by Gardner and Wischik. We follow a recent approach developed by the same authors and previously applied to the pi-calculus for lifting calculi with structural axioms to bialgebraic models. In our model, the unique morphism to the final bialgebra induces a bisimilarity relation which coincides with hyperequivalence and which is a congruence with respect to the operations. Interesting enough, the explicit fusion approach allows to exploit for the Fusion calculus essentially the same algebraic structure used for the pi-calculus
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