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Models and techniques for approximate similarity search in large databasesLinari, Alessandro <1977> 12 April 2007 (has links)
No description available.
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Dynamic services in mobile ad hoc networksMagistretti, Eugenio <1978> 12 April 2007 (has links)
The 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.
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Detecting changes in video sequencesLanza, Alessandro <1973> 26 March 2007 (has links)
No description available.
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Argumentation and artifacts for intelligent multi-agent systemsOliva, Enrico <1976> 07 April 2008 (has links)
Reasoning under uncertainty is a human capacity that in software system
is necessary and often hidden. Argumentation theory and logic make
explicit non-monotonic information in order to enable automatic forms of
reasoning under uncertainty. In human organization Distributed Cognition
and Activity Theory explain how artifacts are fundamental in all cognitive
process. Then, in this thesis we search to understand the use of cognitive
artifacts in an new argumentation framework for an agent-based artificial
society.
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Enabling computationally intensive bioinformatics applications on the Grid platformTrombetti, Gabriele Antonio <1977> 07 April 2008 (has links)
Bioinformatics 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.
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Semantic-based middleware solutions to support context-aware service provisioning in pervasive environmentsToninelli, Alessandra <1979> 07 April 2008 (has links)
The 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.
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Middleware per la gestione di interfacce di comunicazione e di sorgenti di contesto in ambienti wireless eterogeneiGiannelli, Carlo <1979> 07 April 2008 (has links)
The 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.
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Ingegneria di sistemi auto‐organizzanti con il paradigma multiagenteGardelli, Luca <1980> 07 April 2008 (has links)
Self-organisation is increasingly being regarded as an effective approach to tackle
modern systems complexity. The self-organisation approach allows the development of systems exhibiting complex dynamics and adapting to environmental
perturbations without requiring a complete knowledge of the future surrounding
conditions.
However, the development of self-organising systems (SOS) is driven by different principles with respect to traditional software engineering. For instance,
engineers typically design systems combining smaller elements where the composition rules depend on the reference paradigm, but typically produce predictable
results. Conversely, SOS display non-linear dynamics, which can hardly be captured by deterministic models, and, although robust with respect to external
perturbations, are quite sensitive to changes on inner working parameters.
In this thesis, we describe methodological aspects concerning the early-design
stage of SOS built relying on the Multiagent paradigm: in particular, we refer
to the A&A metamodel, where MAS are composed by agents and artefacts, i.e.
environmental resources. Then, we describe an architectural pattern that has
been extracted from a recurrent solution in designing self-organising systems:
this pattern is based on a MAS environment formed by artefacts, modelling
non-proactive resources, and environmental agents acting on artefacts so as to
enable self-organising mechanisms. In this context, we propose a scientific approach for the early design stage of the engineering of self-organising systems:
the process is an iterative one and each cycle is articulated in four stages, modelling, simulation, formal verification, and tuning. During the modelling phase
we mainly rely on the existence of a self-organising strategy observed in Nature
and, hopefully encoded as a design pattern. Simulations of an abstract system model are used to drive design choices until the required quality properties
are obtained, thus providing guarantees that the subsequent design steps would
lead to a correct implementation. However, system analysis exclusively based
on simulation results does not provide sound guarantees for the engineering of
complex systems: to this purpose, we envision the application of formal verification techniques, specifically model checking, in order to exactly characterise the
system behaviours. During the tuning stage parameters are tweaked in order to
meet the target global dynamics and feasibility constraints.
In order to evaluate the methodology, we analysed several systems: in this
thesis, we only describe three of them, i.e. the most representative ones for
each of the three years of PhD course. We analyse each case study using the
presented method, and describe the exploited formal tools and techniques.
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Management and routing algorithms for ad-hoc and sensor networksMonti, Gabriele <1978> 07 April 2008 (has links)
Large scale wireless adhoc
networks of computers, sensors, PDAs etc. (i.e. nodes) are
revolutionizing connectivity and leading to a paradigm shift from centralized systems to highly
distributed and dynamic environments. An example of adhoc
networks are sensor networks, which
are usually composed by small units able to sense and transmit to a sink elementary data which are
successively processed by an external machine. Recent improvements in the memory and
computational power of sensors, together with the reduction of energy consumptions, are rapidly
changing the potential of such systems, moving the attention towards datacentric
sensor networks.
A plethora of routing and data management algorithms have been proposed for the network path
discovery ranging from broadcasting/floodingbased
approaches to those using global positioning
systems (GPS).
We studied WGrid,
a novel decentralized infrastructure that organizes wireless devices in an adhoc
manner, where each node has one or more virtual coordinates through which both message routing
and data management occur without reliance on either flooding/broadcasting operations or GPS.
The resulting adhoc
network does not suffer from the deadend
problem, which happens in
geographicbased
routing when a node is unable to locate a neighbor closer to the destination than
itself.
WGrid
allow multidimensional
data management capability since nodes' virtual coordinates can
act as a distributed database without needing neither special implementation or reorganization. Any
kind of data (both single and multidimensional)
can be distributed, stored and managed. We will
show how a location service can be easily implemented so that any search is reduced to a simple
query, like for any other data type.
WGrid
has then been extended by adopting a replication methodology. We called the resulting
algorithm WRGrid.
Just like WGrid,
WRGrid
acts as a distributed database without needing
neither special implementation nor reorganization and any kind of data can be distributed, stored
and managed. We have evaluated the benefits of replication on data management, finding out, from
experimental results, that it can halve the average number of hops in the network. The direct
consequence of this fact are a significant improvement on energy consumption and a workload
balancing among sensors (number of messages routed by each node). Finally, thanks to the
replications, whose number can be arbitrarily chosen, the resulting sensor network can face sensors
disconnections/connections, due to failures of sensors, without data loss.
Another extension to {WGrid}
is {W*Grid}
which extends it by strongly improving network
recovery performance from link and/or device failures that may happen due to crashes or battery
exhaustion of devices or to temporary obstacles.
W*Grid
guarantees, by construction, at least two disjoint paths between each couple of nodes. This
implies that the recovery in W*Grid
occurs without broadcasting transmissions and guaranteeing
robustness while drastically reducing the energy consumption. An extensive number of simulations
shows the efficiency, robustness and traffic road of resulting networks under several scenarios of
device density and of number of coordinates. Performance analysis have been compared to existent
algorithms in order to validate the results.
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Meta-models, environment and layers: agent-oriented engineering of complex systemsMolesini, Ambra <1980> 07 April 2008 (has links)
Traditional software engineering approaches and metaphors fall short when applied to
areas of growing relevance such as electronic commerce, enterprise resource planning,
and mobile computing: such areas, in fact, generally call for open architectures that
may evolve dynamically over time so as to accommodate new components and meet new
requirements. This is probably one of the main reasons that the agent metaphor and the
agent-oriented paradigm are gaining momentum in these areas.
This thesis deals with the engineering of complex software systems in terms of the
agent paradigm. This paradigm is based on the notions of agent and systems of interacting agents as fundamental abstractions for designing, developing and managing at
runtime typically distributed software systems. However, today the engineer often works
with technologies that do not support the abstractions used in the design of the systems.
For this reason the research on methodologies becomes the basic point in the scientific
activity. Currently most agent-oriented methodologies are supported by small teams of
academic researchers, and as a result, most of them are in an early stage and still in the
first context of mostly \academic" approaches for agent-oriented systems development.
Moreover, such methodologies are not well documented and very often defined and presented only by focusing on specific aspects of the methodology. The role played by meta-
models becomes fundamental for comparing and evaluating the methodologies. In fact a
meta-model specifies the concepts, rules and relationships used to define methodologies.
Although it is possible to describe a methodology without an explicit meta-model, formalising the underpinning ideas of the methodology in question is valuable when checking its
consistency or planning extensions or modifications. A good meta-model must address all
the different aspects of a methodology, i.e. the process to be followed, the work products
to be generated and those responsible for making all this happen. In turn, specifying
the work products that must be developed implies dening the basic modelling building
blocks from which they are built.
As a building block, the agent abstraction alone is not enough to fully model all the
aspects related to multi-agent systems in a natural way. In particular, different perspectives exist on the role that environment plays within agent systems: however, it is
clear at least that all non-agent elements of a multi-agent system are typically considered to be part of the multi-agent system environment. The key role of environment
as a first-class abstraction in the engineering of multi-agent system is today generally
acknowledged in the multi-agent system community, so environment should be explicitly
accounted for in the engineering of multi-agent system, working as a new design dimension
for agent-oriented methodologies. At least two main ingredients shape the environment:
environment abstractions - entities of the environment encapsulating some functions -,
and topology abstractions - entities of environment that represent the (either logical or
physical) spatial structure. In addition, the engineering of non-trivial multi-agent systems requires principles and mechanisms for supporting the management of the system representation complexity. These principles lead to the adoption of a multi-layered description, which could be used by designers to provide different levels of abstraction over
multi-agent systems.
The research in these fields has lead to the formulation of a new version of the SODA
methodology where environment abstractions and layering principles are exploited for en-
gineering multi-agent systems.
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