IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2024-04-18T13:04:14ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2022-12-20T15:51:26Z2023-01-02T13:42:36Zhttp://eprints.imtlucca.it/id/eprint/4084This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/40842022-12-20T15:51:26ZValue creation mechanisms of cloud computing: a conceptual frameworkThe management literature has analysed Cloud Computing, mainly focusing on the impact of its technical properties (e.g. accessibility, elasticity, scaling) on firms' dynamics, without explicitly addressing the dynamic generation of value streams. With this paper we fill this gap, linking the unexplored potential sources of Cloud Computing with the literature on business model value creation. We define a conceptual model able to integrate existent technical knowledge on Cloud Computing with the understudied part on the value creation mechanisms, dynamically representing their interaction. Our approach is based on a mixed methodology built on three pillars:
1) systematic literature review of the properties of Cloud Computing with an impact on firms’ management in order to identify possible gaps, using value generation within business models as the unit of analysis;
2) multiple case studies to inductively derive the emerging properties using Gioia methodology, analysing 20 startups in the AWS business case repository;
3) dynamic representation between technical properties extracted by literature review and emergent properties, focusing on the value streams generation.
Results confirm how the leveraging potentiality of Cloud Computing goes well beyond technical advantages, deeply inserting in the business model system and enabling different sources of value creation.Leonardo Mazzonileonardo.mazzoni@imtlucca.itGabriele Costagabriele.costa@imtlucca.it2020-04-16T09:53:42Z2022-12-20T15:03:26Zhttp://eprints.imtlucca.it/id/eprint/4076This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/40762020-04-16T09:53:42ZSimulation of Covid-19 epidemic evolution:
are compartmental models really predictive?Computational models for the simulation ofthe severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) epidemic evolution would be extremely useful to
support authorities in designing healthcare policies and lockdown measures to
contain its impact on public health and economy. In Italy, the devised forecasts
have been mostly based on a pure data-driven approach, by fitting and
extrapolating open data on the epidemic evolution collected by the Italian Civil
Protection Center. In this respect, SIR epidemiological models, which start from the
description of the nonlinear interactions between population compartments,
would be a much more desirable approach to understand and predict the collective
emergent response. The present contribution addresses the fundamental question
whether a SIR epidemiological model, suitably enriched with asymptomatic and
dead individual compartments, could be able to provide reliable predictions on the
epidemic evolution. To this aim, a machine learning approach based on particle
swarm optimization (PSO) is proposed to automatically identify the model
parameters based on a training set of data of progressive increasing size,
considering Lombardy in Italy as a case study. The analysis of the scatter in the
forecasts shows that model predictions are quite sensitive to the size of the dataset
used for training, and that further data are still required to achieve convergent -
and therefore reliable- predictions.Marco Paggimarco.paggi@imtlucca.it2015-07-22T10:28:33Z2015-09-22T08:14:50Zhttp://eprints.imtlucca.it/id/eprint/2729This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/27292015-07-22T10:28:33ZOn Expressiveness and Behavioural Theory of Attribute-based
CommunicationAttribute-based communication is an interesting alternative to broadcast and binary communication when providing abstract models for the so called Collective Adaptive Systems which consist of a large number of interacting components that dynamically adjust and combine their behavior to achieve specifc goals. A basic process calculus, named AbC, is introduced whose primary
primitive for interaction is attribute-based communication. An AbC system consists of a set of parallel components each of which is equipped with a set of attributes. Communication takes place in an implicit multicast fashion, and interactions among components are dynamically established by taking into account\connections" as determined by predicates over the attributes
exposed by components. First, the syntax and the semantics of AbC are presented, then expressiveness and effectiveness of the calculus are demonstrated both in terms of the ability to model scenarios featuring collaboration, reconfiguration, and adaptation
and of the possibility of encoding a process calculus for broadcasting channel-based communication and other communication
paradigms. Behavioral equivalences for AbC are introduced for establishing formal relationships between different descriptions
of the same system.Yehia Moustafa Abd Alrahmanyehia.abdalrahman@imtlucca.itRocco De Nicolar.denicola@imtlucca.itMichele Loreti2013-08-09T08:02:03Z2015-02-06T10:09:37Zhttp://eprints.imtlucca.it/id/eprint/1655This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/16552013-08-09T08:02:03ZDimming Relations for the Efficient Analysis of Concurrent Systems via Action AbstractionWe study models of concurrency based on labelled transition
systems where abstractions are induced by a partition of the action set. We introduce dimming relations, i.e., notions of behavioural equivalence which are able to relate two models if they can match each other's actions
whenever they are in the same partition block. We show applicability to a number of situations of practical interest which are apparently heterogeneous but exhibit similar behaviors although manifested via different
actions. Dimming relations make the models more homogeneous by collapsing such distinct actions into the same partition block. With our examples, we show how these abstractions permit reducing the state-space complexity from exponential to polynomial in the number of concurrent processes.Rocco De Nicolar.denicola@imtlucca.itGiulio IacobelliMirco Tribastonemirco.tribastone@imtlucca.it2013-06-20T08:03:30Z2013-06-20T08:03:30Zhttp://eprints.imtlucca.it/id/eprint/1620This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/16202013-06-20T08:03:30ZApplying Mean-field Approximation to Continuous Time Markov ChainsThe mean-field analysis technique is used to perform analysis of a systems with a large number of components to determine the emergent deterministic behaviour and how this behaviour modifies when its parameters are perturbed. The computer science performance modelling and analysis community has found the mean-field method useful for modelling large-scale computer and communication networks. Applying mean-field analysis from the computer science perspective requires the following major steps: (1) describing how the agents populations evolve by means of a system of differential equations, (2) finding the emergent
deterministic behaviour of the system by solving such differential equations, and (3) analysing properties of this behaviour either by relying on simulation or by using logics. Depending on the system under analysis, performing these steps may become challenging. Often, modifications
of the general idea are needed. In this tutorial we consider illustrating examples to discuss how the mean-field method is used in different application areas. Starting from the application of the classical technique,
moving to cases where additional steps have to be used, such as systems with local communication. Finally we illustrate the application of the simulation and
uid model checking analysis techniques. Anna KolesnichenkoAlireza PourranjabarValerio Sennivalerio.senni@imtlucca.it2013-05-17T13:45:01Z2013-09-03T08:26:04Zhttp://eprints.imtlucca.it/id/eprint/1588This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/15882013-05-17T13:45:01ZSPoT: Representing the Social, Spatial, and Temporal
Dimensions of Human Mobility with a Unifying FrameworkModeling human mobility is crucial in the analysis and simulation of opportunistic networks, where contacts are exploited as opportunities for peer-topeer message forwarding. The current approach with human mobility modeling has been based on continuously modifying models, trying to embed in them the mobility properties (e.g., visiting patterns to locations or specific distributions of inter-contact times) as they came up from trace analysis. As
a consequence, with these models it is difficult, if not impossible, to modify the features of mobility or to control the exact shape of mobility metrics (e.g., modifying the distribution of inter-contact times). For these reasons, in this paper we propose a mobility framework rather than a mobility model, with the explicit goal of providing a exible and controllable tool for modeling mathematically and generating simulatively different possible features of human mobility. Our framework, named SPoT, is able to incorporate the three dimensions - spatial, social, and temporal - of human mobility. The way SPoT does it is by mapping the different social communities of the network into different locations, whose members visit with a configurable temporal pattern. In order to characterize the temporal patterns of user visits to locations and the relative positioning of locations based on their shared users, we analyze the traces of real user movements extracted from three location-based online social networks (Gowalla, Foursquare, and Altergeo). We observe that a Bernoulli process effectively approximates user visits to locations in the majority of cases and that locations that share many common users visiting them frequently tend to be located close to each other. In addition, we use these traces to test the exibility of the framework, and we show that SPoT is able to accurately reproduce the mobility behavior observed in traces. Finally, relying on the Bernoulli assumption for arrival processes, we provide a throughout mathematical analysis of the controllability of the framework, deriving the conditions under which heavy-tailed and exponentially-tailed aggregate inter-contact times (often observed in real traces) emerge.Dmytro Karamshukdmytro.karamshuk@imtlucca.itChiara BoldriniMarco ContiAndrea Passarella2013-04-19T11:54:44Z2014-03-10T10:42:41Zhttp://eprints.imtlucca.it/id/eprint/1553This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/15532013-04-19T11:54:44ZRevisiting bisimilarity and its modal logic for nondeterministic and probabilistic processesWe consider PML, the probabilistic version of Hennessy-Milner logic introduced by Larsen and Skou to characterize bisimilarity over probabilistic processes without internal
nondeterminism.We provide two different interpretations for PML by considering nondeterministic and probabilistic processes as models, and we exhibit two new bisimulation-based equivalences that are in full agreement with those interpretations. Our new equivalences include
as coarsest congruences the two bisimilarities for nondeterministic and probabilistic processes proposed by Segala and Lynch. The latter equivalences are instead in agreement with two versions of Hennessy-Milner logic extended with an additional probabilistic operator
interpreted over state distributions rather than over individual states. Thus, our new interpretations of PML and the corresponding new bisimilarities offer a uniform framework for reasoning on processes that are purely nondeterministic or reactive probabilistic or are mixing nondeterminism and probability in an alternating/non-alternating way.Marco BernardoRocco De Nicolar.denicola@imtlucca.itMichele Loreti2013-03-19T08:19:38Z2013-04-19T12:43:33Zhttp://eprints.imtlucca.it/id/eprint/1537This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/15372013-03-19T08:19:38ZNetwork-aware Evaluation Environment for Reputation SystemsParties of reputation systems rate each other and use ratings to compute reputation scores that drive their interactions. When deciding which reputation model to deploy in a network environment, it is important to find the
most suitable model and to determine its right initial configuration. This calls for an engineering approach for describing, implementing and evaluating reputation
systems while taking into account specific aspects of both the reputation systems and the networked environment where they will run. We present a software tool (NEVER) for network-aware evaluation of reputation systems and their rapid prototyping through experiments performed according to user-specified parameters. To demonstrate effectiveness of NEVER, we analyse reputation models based on the beta distribution and the maximum likelihood estimation.Alessandro Celestinialessandro.celestini@imtlucca.itRocco De Nicolar.denicola@imtlucca.itFrancesco Tiezzifrancesco.tiezzi@imtlucca.it2013-03-07T11:29:24Z2014-01-08T10:27:41Zhttp://eprints.imtlucca.it/id/eprint/1523This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/15232013-03-07T11:29:24ZRevisiting Trace and Testing Equivalences for Nondeterministic and Probabilistic ProcessesTwo of the most studied extensions of trace and testing equivalences to non-deterministic and probabilistic processes induce distinctions that have been questioned and
lack properties that are desirable. Probabilistic trace-distribution equivalence differentiates systems that can perform the same set of traces with the same probabilities, and is not a congruence for parallel composition. Probabilistic testing equivalence, which relies only
on extremal success probabilities, is backward compatible with testing equivalences for restricted classes of processes, such as fully nondeterministic processes or generative/reactive probabilistic processes, only if specific sets of tests are admitted. In this paper, new versions of probabilistic trace and testing equivalences are presented for the general class of nondeterministic and probabilistic processes. The new trace equivalence is coarser because it compares execution probabilities of single traces instead of entire trace distributions, and turns out to be compositional. The new testing equivalence requires matching all resolutions of nondeterminism on the basis of their success probabilities, rather than comparing
only extremal success probabilities, and considers success probabilities in a trace-by-trace fashion, rather than cumulatively on entire resolutions. It is fully backward compatible with testing equivalences for restricted classes of processes; as a consequence, the trace-
by-trace approach uniformly captures the standard probabilistic testing equivalences for generative and reactive probabilistic processes. The paper discusses in full details the new equivalences and provides a simple spectrum that relates them with existing ones in the
setting of nondeterministic and probabilistic processes.Marco BernardoRocco De Nicolar.denicola@imtlucca.itMichele Loreti2013-02-26T14:19:14Z2015-03-03T09:50:55Zhttp://eprints.imtlucca.it/id/eprint/1493This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/14932013-02-26T14:19:14ZCaSPiS: A Calculus of Sessions, Pipelines and ServicesService-oriented computing is calling for novel computational models and languages with well
disciplined primitives for client-server interaction, structured orchestration and unexpected events handling. We present CaSPiS, a process calculus where the conceptual abstractions of sessioning and pipelining play a central role for modelling service-oriented systems. CaSPiS sessions are two-sided, uniquely named and can be nested. CaSPiS pipelines permit orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner’s side of a session. Several examples are presented to provide evidence of the flexibility of the chosen set of primitives. One key contribution is a fully abstract encoding of Misra et al.’s orchestration language Orc. Another main result shows that in CaSPiS it is possible to program a “graceful termination” of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner.Michele BorealeRoberto BruniRocco De Nicolar.denicola@imtlucca.itMichele Loreti2012-07-24T13:28:47Z2013-04-19T12:42:25Zhttp://eprints.imtlucca.it/id/eprint/1323This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/13232012-07-24T13:28:47ZA uniform framework for modelling nondeterministic, probabilistic, stochastic, or mixed processes and their behavioral equivalencesLabeled transition systems are typically used as behavioral models of concurrent processes, and the labeled transitions define the a one-step state-to-state reachability relation. This model can be made generalized by modifying the transition relation to associate a state reachability distribution, rather than a single target state, with any pair of source state and transition label. The state reachability distribution becomes a function mapping each possible target state to a value that expresses the degree of one-step reachability of that state. Values are taken from a preordered set equipped with a minimum that denotes unreachability. By selecting suitable preordered sets, the resulting model, called ULTraS from Uniform Labeled Transition System, can be specialized to capture well-known models of fully nondeterministic processes (LTS), fully
probabilistic processes (ADTMC), fully stochastic processes (ACTMC), and of nondeterministic and probabilistic (MDP) or nondeterministic and stochastic (CTMDP) processes. This uniform treatment of different behavioral models extends to behavioral equivalences. These can be defined on ULTraS by relying on appropriate measure functions that expresses the degree of reachability of a set of states when performing
single-step or multi-step computations. It is shown that the specializations of bisimulation, trace, and testing
equivalences for the different classes of ULTraS coincide with the behavioral equivalences defined in the literature over traditional models.Marco BernardoRocco De Nicolar.denicola@imtlucca.itMichele Loreti2012-07-24T13:23:26Z2013-04-19T12:42:07Zhttp://eprints.imtlucca.it/id/eprint/1322This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/13222012-07-24T13:23:26ZA uniform definition of stochastic process calculiWe introduce a unifying framework to provide the semantics of process algebras, including their quantitative variants useful for modeling quantitative aspects of behaviors. The unifying framework is then used to describe some of the most representative stochastic process algebras. This
provides a general and clear support for an understanding of their similarities and differences. The framework is based on State to Function Labeled Transition Systems, FuTSs for short, that are state-transition structures where each transition is a triple of the form (s; α;P). The first andthe second components are the source state, s, and the label, α, of the transition, while the third component is the continuation function, P, associating a value of a suitable type to each state s0. For example, in the case of stochastic process algebras the value of the continuation function on s0 represents the rate of the negative exponential distribution characterizing the duration/delay of the action performed to reach state s0 from s. We first provide the semantics of a simple formalism used to describe Continuous-Time Markov Chains, then we model a number of process algebras that permit parallel composition of models according to the two main interaction paradigms (multiparty and one-to-one synchronization). Finally, we deal with formalisms where actions and rates are kept separate and address the issues related to the coexistence of stochastic, probabilistic, and non-deterministic behaviors. For each formalism, we establish the formal correspondence between the FuTSs semantics and its original semantics.Rocco De Nicolar.denicola@imtlucca.itDiego LatellaMichele LoretiMieke Massink