23 research outputs found
DescribeX: A Framework for Exploring and Querying XML Web Collections
This thesis introduces DescribeX, a powerful framework that is capable of
describing arbitrarily complex XML summaries of web collections, providing
support for more efficient evaluation of XPath workloads. DescribeX permits the
declarative description of document structure using all axes and language
constructs in XPath, and generalizes many of the XML indexing and summarization
approaches in the literature. DescribeX supports the construction of
heterogeneous summaries where different document elements sharing a common
structure can be declaratively defined and refined by means of path regular
expressions on axes, or axis path regular expression (AxPREs). DescribeX can
significantly help in the understanding of both the structure of complex,
heterogeneous XML collections and the behaviour of XPath queries evaluated on
them.
Experimental results demonstrate the scalability of DescribeX summary
refinements and stabilizations (the key enablers for tailoring summaries) with
multi-gigabyte web collections. A comparative study suggests that using a
DescribeX summary created from a given workload can produce query evaluation
times orders of magnitude better than using existing summaries. DescribeX's
light-weight approach of combining summaries with a file-at-a-time XPath
processor can be a very competitive alternative, in terms of performance, to
conventional fully-fledged XML query engines that provide DB-like functionality
such as security, transaction processing, and native storage.Comment: PhD thesis, University of Toronto, 2008, 163 page
Parameter Synthesis for Markov Models
Markov chain analysis is a key technique in reliability engineering. A
practical obstacle is that all probabilities in Markov models need to be known.
However, system quantities such as failure rates or packet loss ratios, etc.
are often not---or only partially---known. This motivates considering
parametric models with transitions labeled with functions over parameters.
Whereas traditional Markov chain analysis evaluates a reliability metric for a
single, fixed set of probabilities, analysing parametric Markov models focuses
on synthesising parameter values that establish a given reliability or
performance specification . Examples are: what component failure rates
ensure the probability of a system breakdown to be below 0.00000001?, or which
failure rates maximise reliability? This paper presents various analysis
algorithms for parametric Markov chains and Markov decision processes. We focus
on three problems: (a) do all parameter values within a given region satisfy
?, (b) which regions satisfy and which ones do not?, and (c)
an approximate version of (b) focusing on covering a large fraction of all
possible parameter values. We give a detailed account of the various
algorithms, present a software tool realising these techniques, and report on
an extensive experimental evaluation on benchmarks that span a wide range of
applications.Comment: 38 page
Oblivious Network Optimization and Security Modeling in Sustainable Smart Grids and Cities
Today\u27s interconnected world requires an inexpensive, fast, and reliable way of transferring information. There exists an increasingly important need for intelligent and adaptable routing of network flows. In the last few years, many researchers have worked toward developing versatile solutions to the problem of routing network flows in unpredictable circumstances. These attempts have evolved into a rich literature in the area of oblivious network design which typically route the network flows via a routing scheme that makes use of a spanning tree or a set of trees of the graph representation of the network.
In the first chapter, we provide an introduction to network design. This introductory chapter has been designed to clarify the importance and position of oblivious routing problems in the context of network design as well as its containing field of research. Part I of this dissertation discusses the fundamental role of linked hierarchical data structures in providing the mathematical tools needed to construct rigorous versatile routing schemes and applies hierarchical routing tools to the process of constructing versatile routing schemes. Part II of this dissertation applies the routing tools generated in Part I to address real-world network optimization problems in the area of electrical power networks, clusters of micrograms, and content-centric networks. There is an increasing concern regarding the security and privacy of both physical and communication layers of smart interactive customer-driven power networks, better known as smart grids. Part III of this dissertation utilizes an advanced interdisciplinary approach to address existing security and privacy issues, proposing legitimate countermeasures for each of them from the standpoint of both computing and electrical engineering. The proposed methods are theoretically proven by mathematical tools and illustrated by real-world examples
Heegaard Floer homology and integer surgeries on links
Let L be a link in an integral homology three-sphere. We give a description
of the Heegaard Floer homology of integral surgeries on L in terms of some data
associated to L, which we call a complete system of hyperboxes for L. Roughly,
a complete systems of hyperboxes consists of chain complexes for (some versions
of) the link Floer homology of L and all its sublinks, together with several
chain maps between these complexes. Further, we introduce a way of presenting
closed four-manifolds with b_2^+ > 1 by four-colored framed links in the
three-sphere. Given a link presentation of this kind for a four-manifold X, we
then describe the Ozsvath-Szabo mixed invariants of X in terms of a complete
system of hyperboxes for the link. Finally, we explain how a grid diagram
produces a particular complete system of hyperboxes for the corresponding link.Comment: 231 pages, 54 figures; major revision: we now work with one U
variable for each w basepoint, rather than one per link component; we also
added Section 4, with an overview of the main resul
Monotone Precision and Recall Measures for Comparing Executions and Specifications of Dynamic Systems
The behavioural comparison of systems is an important concern of software
engineering research. For example, the areas of specification discovery and
specification mining are concerned with measuring the consistency between a
collection of execution traces and a program specification. This problem is
also tackled in process mining with the help of measures that describe the
quality of a process specification automatically discovered from execution
logs. Though various measures have been proposed, it was recently demonstrated
that they neither fulfil essential properties, such as monotonicity, nor can
they handle infinite behaviour. In this paper, we address this research problem
by introducing a new framework for the definition of behavioural quotients. We
proof that corresponding quotients guarantee desired properties that existing
measures have failed to support. We demonstrate the application of the
quotients for capturing precision and recall measures between a collection of
recorded executions and a system specification. We use a prototypical
implementation of these measures to contrast their monotonic assessment with
measures that have been defined in prior research
Macaulay inverse systems and Cartan-Kahler theorem
During the last months or so we had the opportunity to read two papers trying
to relate the study of Macaulay (1916) inverse systems with the so-called
Riquier (1910)-Janet (1920) initial conditions for the integration of linear
analytic systems of partial differential equations. One paper has been written
by F. Piras (1998) and the other by U. Oberst (2013), both papers being written
in a rather algebraic style though using quite different techniques. It is
however evident that the respective authors, though knowing the computational
works of C. done during the first half of the last century in a way not
intrinsic at all, are not familiar with the formal theory of systems of
ordinary or partial differential equations developped by D.C. Spencer
(1912-2001) and coworkers around 1965 in an intrinsic way, in particular with
its application to the study of differential modules in the framework of
algebraic analysis. As a byproduct, the first purpose of this paper is to
establish a close link between the work done by F. S. Macaulay (1862-1937) on
inverse systems in 1916 and the well-known Cartan-K{\"a}hler theorem (1934).
The second purpose is also to extend the work of Macaulay to the study of
arbitrary linear systems with variable coefficients. The reader will notice how
powerful and elegant is the use of the Spencer operator acting on sections in
this general framework. However, we point out the fact that the literature on
differential modules mostly only refers to a complex analytic structure on
manifolds while the Spencer sequences have been created in order to study any
kind of structure on manifolds defined by a Lie pseudogroup of transformations,
not just only complex analytic ones. Many tricky explicit examples illustrate
the paper, including the ones provided by the two authors quoted but in a quite
different framework
Advanced human inspired walking strategies for humanoid robots
Cette thèse traite du problème de la locomotion des robots humanoïdes dans le contexte du projet européen KoroiBot. En s'inspirant de l'être humain, l'objectif de ce projet est
l'amélioration des capacités des robots humanoïdes à se mouvoir de façon dynamique et polyvalente. Le coeur de l'approche scientifique repose sur l'utilisation du controle optimal, à la fois pour l'identification des couts optimisés par l'être humain et pour leur mise en oeuvre sur les robots des partenaires roboticiens. Cette thèse s'illustre donc par une collaboration à la fois avec des mathématiciens du contrôle et des spécialistes de la modélisation des primitives motrices. Les contributions majeures de cette thèse reposent donc sur la conception de nouveaux algorithmes temps-réel de contrôle pour la locomotion des robots humanoïdes avec nos collégues de l'université d'Heidelberg et leur intégration sur le robot HRP-2. Deux contrôleurs seront présentés, le premier permettant la locomotion multi-contacts avec une connaissance a priori des futures positions des contacts. Le deuxième étant une extension d'un travail réalisé sur de la marche sur sol plat améliorant les performances et ajoutant des fonctionnalitées au précédent algorithme. En collaborant avec des spécialistes du mouvement humain nous avons implementé un contrôleur innovant permettant de suivre des trajectoires cycliques du centre de masse. Nous présenterons aussi un contrôleur corps-complet utilisant, pour le haut du corps, des primitives de mouvements extraites du mouvement humain et pour le bas du corps, un générateur de marche. Les résultats de cette thèse ont été intégrés dans la suite logicielle "Stack-of-Tasks" du LAAS-CNRS.This thesis covers the topic of humanoid robot locomotion in the frame of the European project KoroiBot. The goal of this project is to enhance the ability of humanoid robots
to walk in a dynamic and versatile fashion as humans do. Research and innovation studies in KoroiBot rely on optimal control methods both for the identification of cost
functions used by human being and for their implementations on robots owned by roboticist partners. Hence, this thesis includes fruitful collaborations with both control
mathematicians and experts in motion primitive modeling. The main contributions of this PhD thesis lies in the design of new real time controllers for humanoid robot locomotion
with our partners from the University of Heidelberg and their integration on the HRP-2 robot. Two controllers will be shown, one allowing multi-contact locomotion with a
prior knowledge of the future contacts. And the second is an extension of a previous work improving performance and providing additional functionalities. In a
collaboration with experts in human motion we designed an innovating controller for tracking cyclic trajectories of the center of mass. We also show a whole body controller
using upper body movement primitives extracted from human behavior and lower body movement computed by a walking pattern generator. The results of this thesis have been
integrated into the LAAS-CNRS "Stack-of-Tasks" software suit