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2004 Contribution to book Restricted

Architectural challenges for a dependable information society
Simoncini L., Di Giandomenico F., Bondavalli A., Chiaradonna S.
This paper is two-fold. In the first part it tries to raise awareness on the level of complexity of future computer-based interconnected systems/infrastructures, at least as they are envisioned, and on the level of dependability we are today able to justify with confidence. It tries to motivate that fundamental methods and methodologies must be reconsidered, studied, exploited, assessed and applied to move towards an utopia that can be called "ambient dependability", a global view of the concept of dependability [Laprie, 1992], which encompasses not only the technological aspects but includes inter and multi disciplinary fields, which span over ergonomics, usability, education, sociology, law and government. The second part of the paper provides the authors views, based on their experience, on future directions and architectural challenges to be tackled for approaching, as a first step towards ambient dependability, at least an Information Society which we can depend on.Source: Building the Information Society, edited by Jacquart, R (Editor), pp. 283–304. Boston: Kluwer Academic Publishers, 2004

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2001 Journal article Restricted

Design validation of embedded dependable systems
Bondavalli A., Fantechi A., Latella D., Simoncini L.
Embedded complex systems require an integrated and best-balanced set of components. to use these components requires some sort of verifiable compositionality, a concept that implies the preservation of properties and the ability to verify them.Source: IEEE MICRO 21 (2001): 52–62.

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2001 Conference article Restricted

Modeling and analysis of the behavior of GPRS systems
Tataranni F., Porcarelli S., Di Giandomenico F., Bondavalli A., Simoncini L.
The General Packet Radio Service (GPRS) has recently become a standard to extend the services provided by the Global System for Mobile Communications (GSM). GPRS addresses packet-oriented traffic, by allowing a more efficient usage of the radio resources with a consequent improvement in the QoS of subscribers. This paper focuses on a preliminary evaluation of dependability and performance figures of the GPRS, by analyzing its behavior during the contention phase where users compete for the channel reservation. The presented work constitutes the first step towards the analysis of the GPRS under critical conditions, as determined by periods of outages, which significantly impact on the dependability, of the GPRS itself. In fact, outages imply service unavailability, with a consequent accumulation of users actively waiting for making a service request, leading to a higher probability of collisions on requests (and therefore a degradation of the QoS perceived by the users) when the system comes back up again. Here, some analyses have been performed, using a simulation approach, to gain insights on appropriate settings for the GPRS, at varying values of internal and external system conditions.Source: 6th International Workshop on Object-Oriented Real-Time Dependable Systems (Words), pp. 51–58, Roma, Italy, January 2001

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2000 Conference article Open Access OPEN

An integrated and compositional approach to design validation of embedded dependable systems
Bondavalli A., Fantechi A., Latella D., Simoncini L.
Complex systems require the use of an inte-grated and best-balanced set of components. The integration and the balanced set are crucial issues, which require some sort of verifiable compositionality property of components that contribute structurally, functionally, non functionally and interactionally to the total quality of the system design. This is even more important when dealing with highly dependable systems. The concept of verifiable compositionality is much more demanding than the usual approach based on composition of building blocks. It implies the preservation of properties and the ability of verifying them. Economic reasons push towards the use of COTS (Commercial Off the Shelf) and towards the re-use of available components, this trend poses new problems. Integration, compositionality and re-use appear to be the very challenging issues in the validation (of both design and implementation) of complex systems, in particular of dependable ones used for controlling critical applications. They require a special effort towards the emergence of a new discipline - System Engineering - which will encompass and integrate the current design disciplines. This paper aims at a discussion in the direction of identifying possible advanced approaches to the validation of dependable systems.Source: IEEE International Workshop On Embedded Fault-Tolerant Systems, Washington D.C., USA, 2000

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2000 Conference article Restricted

Consensus in asynchronous distributed systems: a concise guided tour
Coccoli A., Bondavalli A., Simoncini L.
It is now recognized that the Consensus problem is a fundamental problem when one has to design and implement reliable asynchronous distributed systems. This chapter is on the Consensus problem. It studies Consensus in two failure models, namely, the Crash/no Recovery model and the Crash/Recovery model. The assumptions related to the detection of failures that are required to solve Consensus in a given model are particularly emphasized. © Springer-Verlag Berlin Heidelberg 2000.Source: IDPT '2000 5th, International Conference on Integrated Design and Process Technology, pp. 33–47, Dallas, TX-USA, June 4-8 2000

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2000 Journal article Restricted

Hierarchical modelling of complex control systems: dependability analysis of a railway interlocking
Bondavalli A., Nelli M., Simoncini L., Mongardi G.
This paper reports an experience made in building a model and analysing the dependability of an actual railway station interlocking control system. Despite our analysis has been restricted to the Safety Nucleus subsystem, mastering complexity and size required a considerable effort. We identified a modelling strategy, based on a modular, hierarchical decomposition allowing to use different methods and tools for modelling at the various level of the hierarchy. This multi-layered modelling methodology led to an accurate representation of the system behaviour and allowed us (i) to keep under control the size of the models within the different levels to be easily managed by the automatic tools, (ii) to make changes in the model in a very easy and cheap way. The paper contains also examples of the extensive analyses performed regarding the sensitivity of the dependability measures to variations of critical parameters and towards the validation of the assumptions made.Source: International journal of computer science, systems engineering and information technology (2000): 249–261.

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1999 Conference article Restricted

Towards a discipline of system engineering: validation of dependable systems
Bondavalli A., Fantechi A., Latella D., Simoncini L.
An abstract is not available.Source: Computer security, dependability & assurance: from needs to solutions, pp. 144–164, 1999

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1999 Conference article Restricted

Towards a discipline of systems engineering: validation of dependable systems architectures
Simoncini L.
An abstract is not available.Source: Computer Security, Dependability, & Assurance: from Needs to solutions, 1999

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1998 Journal article Open Access OPEN

Temporal analysis of data flow control systems
Bernardeschi C., Bondavalli A., Csertan G., Majzik I., Simoncini L.
Due to their distributed/parallel and data-driven nature, control systems can easily be modeled according to a data flow approach. Control systems are very often real-time systems; therefore, a formalism able to capture timing is required. In this paper we introduce a data flow model that includes time and priority for specifying real-time control systems and we give its formal semantics. The control system is specified by a data flow network which, beside the controller, may include the model of the plant at some abstraction level. Time is associated to any computational activity and time accounting is made directly in the model and not as a separate issue. Priorities allow to deal with events, as alarm signals, which cannot be delayed. A general framework for the indirect evaluation of the model is introduced, and a data flow network to timed Petri net transformation is defined allowing the utilization of the automatic tools of Petri nets for analyzing the temporal properties of the data flow network. The approach is illustrated by an example in which, after the application of the transformation, selected performance measures are computed. © 1998 Elsevier Science Ltd. All rights reserved.Source: Automatica (Oxf.) 34 (1998): 169–182. doi:10.1016/S0005-1098(97)00176-3
DOI: 10.1016/s0005-1098(97)00176-3

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1996 Other Open Access OPEN

Hierarchical Modelling of HW/SW Control Systems: an Application to Dependability Analysis of Railway Interlocking
Nelli M., Bondavalli A., Simoncini L.
This paper describes the dependability modelling and evaluation of a real complex system, made of redundant replicated hardware and redundant diverse software. It takes into account all aspects of their interactions (including correlation between the diverse software variants) and of the criticality of the several components. Our approach has been to realise the system model in a structured way. This allow to cope with complexity and to focus, where interesting, on specific behaviour for a more detailed analysis. Furthermore each level may be modelled using different methodologies and its evaluation performed with different tools without the need of modifying the general structure of the model. In order to validate the most complex sub-models, we built alternatives using different tools and methodologies; this proved to be very useful since it allowed to find small bugs and imperfections and to gain more confidence that the models represented the real system behaviour. With respect to the real system taken as the example, our analyses allowed to establish the dependability bottlenecks of the current version and to state targets for the several sub-components such that the system targets could be reached, thus providing hints for next releases or modifications of the system and information to assign targets to the various components of the system.

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1993 Other Open Access OPEN

A semantic model of data flow networks based on process algebras
Bernardeschi C., Bondavalli A., Simoncini L.
Data flow networks are a paradigm for concurrent computations in which a collection of parallel processes communicate asynchronously. For data flow many compositional semantics models have been defined, however, it is extremely complex to reason about their semantic behaviour. To perform the semantic analysis of data flow networks, we define a transformation from data flow to specifications in the process algebras formalism which preserves the traces of the networks. The main contribution of the paper lies in the possibility of applying the theory and tools developed for the process algebras formalism in the analysis of data flow networks. Keywords Parallel Programs: formal program development methodologies, specification and verification; Parallel Programming Languages: Semantics

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1987 Other Open Access OPEN

Protection in DELTA-4
Ciompi P., Grandoni F., Simoncini L.
No abstract available

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1987 Contribution to book Restricted

The evolution of dependable computing in Italy
Ciompi P., Grandoni F., Strigini L., Simoncini L.
This brief history of the evolution of dependable computing in Italy begins at the end of the sixties with the need to produce test sequences and testing tools to verify hardware implemented using discrete components. The growing interest of the Italian computer science and engineering community in dependability issues has produced several joint studies and development ventures between industrial and academic partners. This paper will survey the main scientific and technical results obtained during this period.Source: The Evolution of Fault-Tolerant Computing, edited by Avizienis A., Kopetz H., Laprie J.C., pp. 374–407. WIEN: SPRINGER-VERLAG, 1987
DOI: 10.1007/978-3-7091-8871-2_16

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1986 Other Open Access OPEN

DELTA-4: overall system specification
Ciompi P., Grandoni F., Simoncini L., Bonn G., Martin P., Powell D., Seaton D.
No abstract available

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1986 Other Open Access OPEN

A gracefully degradable algorithm for byzantine agreement
Di Giandomenico F., Guidotti M., Grandoni F., Simoncini L.
An algorithm for the Byzantine Agreement without authentication in a set of n processes is presented. This algorithm has the peculiarity of being more efficient as less malicious the behaviour of the faulty processes is and less the number of actual faulty processes is. If the number of actually faulty processes is less of t/2 (t is the maximum allowable number of faulty processes) it is shown that the proposed algorithm converges very quickly to the agreement. In a system composed of 3t processes and one sender process, if at most Lt/2J+1 faulty processes are present (except the sender), reaching the agreement requires 3 rounds and 2(n-1) messages exchanged per process. A comparison with known algorithms based on similar hypotheses is performed.

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1986 Other Open Access OPEN

Algoritmi affidabili per multicasts su token ring
Scevarolli M., Simoncini L.
Negli ultimi anni con la evoluzione dei sistemi di calcolatori, ed in particolare dei sistemi di comunicazione su cui sono basati, si è evidenziata la necessità di offrire primitive di comunicazione sempre più potenti, ma soprattutto affidabili.

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1986 Other Open Access OPEN

Algoritmi affidabili per broadcast tolleranti i partizionamenti
Scevarolli M., Simoncini L.
Il partizionamento è un problema non secondario delle moderne reti di calcolatori, in quanto può essere facilmente causato da fallimenti (anche temporanei) di nodi o link, ma anche da "intasamenti" di zone cruciali che, rallentando o bloccando il flusso dei messaggi provocano effetti analoghi. Per molte applicazioni è importante comprendere almeno a chi un dato messaggio può non essere arrivato, in modo da evitare azioni che possano generare nuovi e più gravi errori, ed attivare politiche ad hoc. In questa nota ci si è occupati di come tollerare questo problema, e si sono individuati due possibili estensioni del protocollo di broadcast atomico in /CASD/.

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1986 Other Open Access OPEN

Proposta per una architettura robusta Data-Flow Like
Bondavalli A., Simoncini L.
In questo lavoro vengono proposti una implementazione ed un sistema di tolleranza ai guasti relativi al linguaggio presentato in [Bon86] Da una analisi sulle caratteristiche del linguaggio vengono dedotte funzionalità della macchina astratta quali interprete, instradamento dei messaggi e gestione delle risorse. Viene quindi proposta una architettura che possa essere la base per una efficiente implementazione; questa proposta è parziale in quanto l'interno dei moduli non è stato definito e vengono discusse le ripercussioni che questa eventuale definizione ha sulla implementazione. Si affrontano poi le problematiche della tolleranza ai guasti e della robustezza, vengono svolte considerazioni sulle caratteristiche di robustezza del linguaggio e sulle capacità richieste al livello hardware del sistema per la scoperta ed il mascheramento. Viene infine proposta una strategia per la tolleranza ai guasti molto semplice ed efficace.

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1986 Other Open Access OPEN

Linguaggio per un ambiente di programmazione Data-Flow like
Bondavalli A., Simoncini L.
Viene presentata una ossatura di linguaggio la cui strutturazione consente di ottenere un ambiente di programmazione ad alto parallelismo e robusto; ambente che viene poi arricchito inserendo nel linguaggio costrutti per gestire non-determinismo e permettendo di eseguire computazioni con stato. Per favorire il parallelismo e la velocità del sistema viene abbandonato il modello computazionale tradizionalmente usato: il modello Control-Flow, cioé con flusso di controllo guidato dal programma; e si ricorre al modello computazionale col flusso di controllo guidato dai dati: il Data-Flow. Il non-determinismo viene espresso tramite la definizione di costrutti che si rifanno ai programmi con guardia di Dijkstra e le computazioni con stato, le cosiddette history sensitive computations, sono esprimibili per il fatto che viene consentito al grafo che le rappresenta di avere cicli.

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1986 Journal article Restricted

L'automazione nell'SDI
Simoncini L.
In questo articolo viene descritta la struttura dell'attuale sistema di comando e controllo per le armi strategiche degli Stati Uniti, evidenziando le componenti basate sull'uso di elaboratori elettronici e discutendone l'affidabilità.Source: Sapere (Bari) 52 (1986): 35–43.

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