1,720,974 research outputs found
Sistemi Operativi. Seconda edizione
No full textIl libro è specificamente concepito come testo per un primo insegnamento sui sistemi operativi che rappresenta una parte essenziale di ogni corso di laurea in Ingegneria Informatica ed Informatica. Rispetto alla prima edizione il libro e' stato arricchito di un nuovo capitolo sulle problematiche di protezione e sicurezza e di due nuove appendici, una relativa al linguaggio dei comandi (shell) di Unix ed una relativa ai sitemi sommersi (embedded). Inoltre sono stati approfonditi alcuni argomenti chiave come ,per esempio, gli algoritmi di scheduling della CPU, le tecniche di gestione delle condizioni di stallo ed i sistemi operativi real-time
Structural analysis of combinatorial optimization problem characteristics and their resolution using hybrid approaches
No full textMany combinatorial problems coming from the real world may not have a clear and well defined structure, typically being dirtied by side constraints, or being composed of two or more sub-problems, usually not disjoint. Such problems are not suitable to be solved with pure approaches based on a single programming paradigm, because a paradigm that can effectively face a problem characteristic may behave
inefficiently when facing other characteristics. In these cases, modelling the problem using different programming techniques, trying to ”take the best” from each technique, can produce solvers that largely dominate pure approaches. We demonstrate the effectiveness of hybridization and we discuss about different hybridization techniques by analyzing two classes of problems with particular structures, exploiting Constraint Programming and Integer Linear Programming solving tools and Algorithm Portfolios and Logic Based Benders Decomposition as integration and
hybridization frameworks
Middleware principles and design for the integration of ubiquitos mobile services
No full textNowadays, in Ubiquitous computing scenarios users more and more require to exploit online contents and services by means of any device at hand, no matter their physical location, and by personalizing and tailoring content and service access to their own requirements. The coordinated provisioning of content tailored to user context and preferences, and the support for mobile multimodal and multichannel interactions are of paramount importance in providing users with a truly effective Ubiquitous support.
However, so far the intrinsic heterogeneity and the lack of an integrated approach led to several either too vertical, or practically unusable proposals, thus resulting in poor and non-versatile support platforms for Ubiquitous computing.
This work investigates and promotes design principles to help cope with these ever-changing and inherently dynamic scenarios. By following the outlined principles, we have designed and implemented a middleware support platform to support the provisioning of Ubiquitous mobile services and contents. To prove the viability of our approach, we have realized and stressed on top of our support platform a number of different, extremely complex and heterogeneous content and service provisioning scenarios.
The encouraging results obtained are pushing our research work further, in order to provide a dynamic platform that is able to not only dynamically support novel Ubiquitous applicative scenarios by tailoring extremely diverse services and contents to heterogeneous user needs, but is also able to reconfigure and adapt itself in order to provide a truly optimized and tailored support for Ubiquitous service provisioning
Enabling computationally intensive bioinformatics applications on the Grid platform
No full textBioinformatics is a recent and emerging discipline which aims at studying
biological problems through computational approaches. Most branches of
bioinformatics such as Genomics, Proteomics and Molecular Dynamics are
particularly computationally intensive, requiring huge amount of
computational resources for running algorithms of everincreasing
complexity over data of everincreasing
size.
In the search for computational power, the EGEE Grid platform, world's
largest community of interconnected clusters load balanced as a whole,
seems particularly promising and is considered the new hope for satisfying
the everincreasing
computational requirements of bioinformatics, as well as
physics and other computational sciences.
The EGEE platform, however, is rather new and not yet free of problems. In
addition, specific requirements of bioinformatics need to be addressed in
order to use this new platform effectively for bioinformatics tasks.
In my three years' Ph.D. work I addressed numerous aspects of this Grid
platform, with particular attention to those needed by the bioinformatics
domain.
I hence created three major frameworks, Vnas, GridDBManager and
SETest, plus an additional smaller standalone solution, to enhance the
support for bioinformatics applications in the Grid environment and to
reduce the effort needed to create new applications, additionally addressing
numerous existing Grid issues and performing a series of optimizations.
The Vnas framework is an advanced system for the submission and
monitoring of Grid jobs that provides an abstraction with reliability over the
Grid platform. In addition, Vnas greatly simplifies the development of new
Grid applications by providing a callback system to simplify the creation of
arbitrarily complex multistage
computational pipelines and provides an
abstracted virtual sandbox which bypasses Grid limitations. Vnas also
reduces the usage of Grid bandwidth and storage resources by
transparently detecting equality of virtual sandbox files based on content,
across different submissions, even when performed by different users.
BGBlast, evolution of the earlier project GridBlast, now provides a Grid
Database Manager (GridDBManager) component for managing and
automatically updating biological flatfile
databases in the Grid environment.
GridDBManager sports very novel features such as an adaptive replication
algorithm that constantly optimizes the number of replicas of the managed
databases in the Grid environment, balancing between response times
(performances) and storage costs according to a programmed cost formula.
GridDBManager also provides a very optimized automated management for
older versions of the databases based on reverse delta files, which reduces
the storage costs required to keep such older versions available in the Grid
environment by two orders of magnitude.
The SETest framework provides a way to the user to test and
regressiontest
Python applications completely scattered with side effects
(this is a common case with Grid computational pipelines), which could not
easily be tested using the more standard methods of unit testing or test
cases. The technique is based on a new concept of datasets containing
invocations and results of filtered calls. The framework hence significantly
accelerates the development of new applications and computational
pipelines for the Grid environment, and the efforts required for maintenance.
An analysis of the impact of these solutions will be provided in this thesis.
This Ph.D. work originated various publications in journals and conference
proceedings as reported in the Appendix. Also, I orally presented my work
at numerous international conferences related to Grid and bioinformatics
Middleware per la gestione di interfacce di comunicazione e di sorgenti di contesto in ambienti wireless eterogenei
No full textThe full exploitation of multi-hop multi-path connectivity opportunities offered
by heterogeneous wireless interfaces could enable innovative Always Best Served
(ABS) deployment scenarios where mobile clients dynamically self-organize to
offer/exploit Internet connectivity at best. Only novel middleware solutions based
on heterogeneous context information can seamlessly enable this scenario:
middleware solutions should i) provide a translucent access to low-level
components, to achieve both fully aware and simplified pre-configured
interactions, ii) permit to fully exploit communication interface capabilities, i.e.,
not only getting but also providing connectivity in a peer-to-peer fashion, thus
relieving final users and application developers from the burden of directly
managing wireless interface heterogeneity, and iii) consider user mobility as
crucial context information evaluating at provision time the suitability of available
Internet points of access differently when the mobile client is still or in motion.
The novelty of this research work resides in three primary points. First of all, it
proposes a novel model and taxonomy providing a common vocabulary to easily
describe and position solutions in the area of context-aware autonomic
management of preferred network opportunities.
Secondly, it presents PoSIM, a context-aware middleware for the synergic
exploitation and control of heterogeneous positioning systems that facilitates the
development and portability of location-based services. PoSIM is translucent, i.e.,
it can provide application developers with differentiated visibility of data
characteristics and control possibilities of available positioning solutions, thus
dynamically adapting to application-specific deployment requirements and
enabling cross-layer management decisions.
Finally, it provides the MMHC solution for the self-organization of multi-hop
multi-path heterogeneous connectivity. MMHC considers a limited set of practical
indicators on node mobility and wireless network characteristics for a coarsegrained
estimation of expected reliability/quality of multi-hop paths available at
runtime. In particular, MMHC manages the durability/throughput-aware formation
and selection of different multi-hop paths simultaneously. Furthermore, MMHC
provides a novel solution based on adaptive buffers, proactively managed based on
handover prediction, to support continuous services, especially by pre-fetching
multimedia contents to avoid streaming interruptions
Uniquitous internet middleware: architecture design and prototype evaluation
No full textTechnology advances in recent years have dramatically changed the way users exploit contents and services available on the Internet, by enforcing pervasive and mobile computing scenarios and enabling access to networked resources almost from everywhere, at anytime, and independently of the device in use. In addition, people increasingly require to customize their experience, by exploiting specific device capabilities and limitations, inherent features of the communication channel in use, and interaction paradigms that significantly differ from the traditional request/response one.
So-called Ubiquitous Internet scenario calls for solutions that address many different challenges, such as device mobility, session management, content adaptation, context-awareness and the provisioning of multimodal interfaces. Moreover, new service opportunities demand simple and effective ways to integrate existing resources into new and value added applications, that can also undergo run-time modifications, according to ever-changing execution conditions.
Despite service-oriented architectural models are gaining momentum to tame the increasing complexity of composing and orchestrating distributed and heterogeneous functionalities, existing solutions generally lack a unified approach and only provide support for specific Ubiquitous Internet aspects. Moreover, they usually target rather static scenarios and scarcely support the dynamic nature of pervasive access to Internet resources, that can make existing compositions soon become obsolete or inadequate, hence in need of reconfiguration.
This thesis proposes a novel middleware approach to comprehensively deal with Ubiquitous Internet facets and assist in establishing innovative application scenarios. We claim that a truly viable ubiquity support infrastructure must neatly decouple distributed resources to integrate and push any kind of content-related logic outside its core layers, by keeping only management and coordination responsibilities. Furthermore, we promote an innovative, open, and dynamic resource composition model that allows to easily describe and enforce complex scenario requirements, and to suitably react to changes in the execution conditions
Semantic-based middleware solutions to support context-aware service provisioning in pervasive environments
No full textThe dynamicity and heterogeneity that characterize pervasive environments raise new challenges in the design of mobile middleware. Pervasive environments are characterized by a
significant degree of heterogeneity, variability, and dynamicity that conventional middleware
solutions are not able to adequately manage. Originally designed for use in a relatively static
context, such middleware systems tend to hide low-level details to provide applications with
a transparent view on the underlying execution platform. In mobile environments, however,
the context is extremely dynamic and cannot be managed by a priori assumptions. Novel
middleware should therefore support mobile computing applications in the task of adapting their behavior to frequent changes in the execution context, that is, it should become
context-aware.
In particular, this thesis has identified the following key requirements for novel
context-aware middleware that existing solutions do not fulfil yet. (i) Middleware solutions
should support interoperability between possibly unknown entities by providing expressive
representation models that allow to describe interacting entities, their operating conditions
and the surrounding world, i.e., their context, according to an unambiguous semantics.
(ii) Middleware solutions should support distributed applications in the task of reconfiguring and adapting their behavior/results to ongoing context changes. (iii) Context-aware
middleware support should be deployed on heterogeneous devices under variable operating
conditions, such as different user needs, application requirements, available connectivity
and device computational capabilities, as well as changing environmental conditions.
Our main claim is that the adoption of semantic metadata to represent context
information and context-dependent adaptation strategies allows to build context-aware middleware suitable for all dynamically available portable devices. Semantic metadata provide
powerful knowledge representation means to model even complex context information, and
allow to perform automated reasoning to infer additional and/or more complex knowledge
from available context data. In addition, we suggest that, by adopting proper configuration
and deployment strategies, semantic support features can be provided to differentiated users
and devices according to their specific needs and current context.
This thesis has investigated novel design guidelines and implementation options
for semantic-based context-aware middleware solutions targeted to pervasive environments.
These guidelines have been applied to different application areas within pervasive computing
that would particularly benefit from the exploitation of context. Common to all applications
is the key role of context in enabling mobile users to personalize applications based on their
needs and current situation.
The main contributions of this thesis are (i) the definition of a metadata model
to represent and reason about context, (ii) the definition of a model for the design and
development of context-aware middleware based on semantic metadata, (iii) the design of
three novel middleware architectures and the development of a prototypal implementation
for each of these architectures, and (iv) the proposal of a viable approach to portability
issues raised by the adoption of semantic support services in pervasive applications
Support infrastructures for multimedia services with guaranteed continuity and QoS
No full textAdvances in wireless networking and content delivery systems are enabling new challenging provisioning scenarios where a growing number of users access multimedia services, e.g., audio/video streaming, while moving among different points of attachment to the Internet, possibly with different connectivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to
discontinuities in wireless resource availability due to handoffs. This dissertation proposes a novel middleware solution, called MUM, that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. To achieve the goal, MUM exploits the full visibility of wireless connections available in client localities and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality degradations (QoS awareness), and of network topology and resources available in current/future localities (location awareness). The design and implementation of the all main MUM components along with extensive on the field trials of the realized middleware architecture confirmed the validity of the proposed full
context-aware handoff management approach. In particular, the reported experimental results demonstrate that MUM can effectively maintain service continuity for a wide range of different multimedia services by exploiting handoff prediction mechanisms, adaptive buffering and pre-fetching techniques, and proactive re-addressing/re-binding
Dynamic services in mobile ad hoc networks
No full textThe increasing diffusion of wireless-enabled portable devices is pushing toward the design of novel service scenarios, promoting temporary and opportunistic interactions in infrastructure-less environments. Mobile Ad Hoc Networks (MANET) are the general model of these higly dynamic networks that can be specialized, depending on application cases, in more specific and refined models such as Vehicular Ad Hoc Networks and Wireless Sensor Networks. Two interesting deployment cases are of increasing relevance: resource diffusion among users equipped with portable devices, such as laptops, smart phones or PDAs in crowded areas (termed dense MANET) and dissemination/indexing of monitoring information collected in Vehicular Sensor Networks. The extreme dynamicity of these scenarios calls for novel distributed protocols and services facilitating application development. To this aim we have designed middleware solutions supporting these
challenging tasks. REDMAN manages, retrieves, and disseminates replicas of software resources in dense MANET; it implements novel lightweight protocols to maintain a desired replication degree despite participants mobility, and efficiently perform resource retrieval. REDMAN exploits the high-density assumption to achieve scalability and limited network overhead. Sensed data gathering and distributed indexing in Vehicular Networks raise similar
issues: we propose a specific middleware support, called MobEyes, exploiting node mobility to opportunistically diffuse data summaries among neighbor vehicles. MobEyes
creates a low-cost opportunistic distributed index to query the distributed storage and to determine the location of needed information. Extensive validation and testing of REDMAN and MobEyes prove the effectiveness of our original solutions in limiting communication overhead while maintaining the required accuracy of replication degree and indexing completeness, and demonstrates the feasibility of the middleware approach
Evoluzione dei Sistemi Operativi. Secoda parte:categorie particolari
No full textEsaminate nella prima parte le motivazioni che hanno influenzato l'evoluzione del concetto stesso di sistema operativo dono ora messe in evidenza le motivazioni che hanno portato all'evoluzione di particolari categorie di sistemi operativi da quello per personal computer ai sistemi real time e embedded,dai sistemi operativi di rete e distribuiti a quelli per la generazione di macchine virtuali
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