1,720,969 research outputs found
Parameterized Verification and Synthesis for Distributed Agreement-Based Systems
No full textDistributed agreement-based systems use common distributed agreement protocols such as leader election and consensus as building blocks for their target functionality—processes in these systems may need to agree on a leader, on the members of a group, on owners of locks, or on updates to replicated data. Such distributed agreement-based systems are common and potentially permit modular, scalable verification approaches that mimic their modular design. Interestingly, while there are many verification efforts that target agreement protocols themselves, little attention has been given to distributed agreement-based systems that build on top of these protocols.In this work, we aim to develop a fully-automated, modular, and usable parameterized verification approach for distributed agreement-based systems. To do so, we need to overcome the following challenges. First, the fully automated parameterized verification problem, i.e, the problem of algorithmically checking if the system is correct for any number of processes, is a well-known undecidable problem. Second, to enable modular verification that leverages the inherently-modular nature of these agreement-based systems, we need to be able to support abstractions of agreement protocols. Such abstractions can replace the agreement protocols’ implementations when verifying the overall system; enabling modular reasoning. Finally, even when the verification is fully automated, a system designer still needs assistance in modelingtheir distributed agreement-based systems.We systematically tackle these challenges through the following contributions.First, we support efficient, decidable verification of distributed agreement-based systems by developing a computational model—the GSP model—for reasoning about distributed (agreement-based) systems that admits decidability and cutoffresults. Cutoff results enable practical verification by reducing the parameterized verification problem to the verification problem of a system with a fixed, finite number of processes. The GSP model supports generalized communication primitives and global guards, both of which are essential to enable abstractions of agreement protocols.Then, we address the usability and modularity aspects by developing a framework, QuickSilver, tailored for modeling and modular parameterized verification of distributed agreement-based systems. QuickSilver provides an intuitive domain-specific language, called Mercury, that is equipped with two agreement primitives capable of abstracting away agreement protocols when modeling agreement-based systems; enabling modular verification. QuickSilver extends the decidability and cutoff results of the GSP model to provide fully automated, efficient parameterized verification for a large class of systems modeled in Mercury.Finally, we leverage synthesis techniques to further enhance the usability of our approach and propose Cinnabar, a tool that supports synthesis of distributed agreement-based systems with efficiently-decidable parameterized verification. Cinnabar allows a system designer to provide a sketch of their Mercury model and uses a counterexample-guided synthesis procedure to search for model completions that both belong to the efficiently-decidable fragment of Mercury and are correct.We evaluate our contributions on various interesting distributed agreement-based systems adapted from real-world applications, such as a data store, a lock service, a surveillance system, a pathfinding algorithm for mobile robots, and more
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Program reliability through algorithmic design and analysis
Get PDFtextSoftware systems are ubiquitous in today's world and yet, remain vulnerable to the fallibility of human programmers as well as the unpredictability of their operating environments. The overarching goal of this dissertation is to develop algorithms to enable automated and efficient design and analysis of
reliable programs.
In the first and second parts of this dissertation, we focus on the development of programs that are free from programming errors. The intent is not to eliminate the human programmer, but instead to complement his or her expertise, with sound and efficient computational techniques, when possible. To this end, we make contributions in two specific domains.
Program debugging --- the process of fault localization and error elimination from a program found to be incorrect --- typically relies on expert human intuition and experience, and is often a lengthy, expensive part of the program development cycle. In the first part of the dissertation, we target automated debugging of sequential programs. A broad and informal statement of the (automated) program debugging problem is to suitably modify an
erroneous program, say P, to obtain a correct program, say P'. This problem is undecidable in general; it is hard to formalize; moreover, it is particularly challenging to assimilate and mechanize the customized, expert
programmer intuition involved in the choices made in manual program debugging. Our first contribution in this domain is a methodical formalization of the program debugging problem, that enables automation, while incorporating expert programmer intuition and intent. Our second contribution is a solution framework that can debug infinite-state, imperative, sequential programs written in higher-level programming languages such as C. Boolean programs, which are smaller, finite-state abstractions of infinite-state or large, finite-state programs, have been found to be tractable for program verification. In this dissertation, we utilize Boolean programs for program debugging. Our solution framework involves two main steps: (a) automated debugging of a Boolean program, corresponding to an erroneous program P, and (b) translation of the corrected Boolean program into a correct program P'.
Shared-memory concurrent programs are notoriously difficult to write, verify
and debug; this makes them excellent targets for automated program
completion, in particular, for synthesis of synchronization code. Extant work
in this domain has focused on either propositional temporal logic specifications with simplistic models of concurrent programs, or more refined
program models with the specifications limited to just safety properties. Moreover, there has been limited effort in developing adaptable and fully-automatic synthesis frameworks that are capable of generating synchronization at different levels of abstraction and granularity. In the
second part of this dissertation, we present a framework for synthesis of
synchronization for shared-memory concurrent programs with respect to temporal logic specifications. In particular, given a concurrent program composed of synchronization-free processes, and a temporal logic specification describing their expected concurrent behaviour, we generate synchronized processes such
that the resulting concurrent program satisfies the specification. We
provide the ability to synthesize readily-implementable synchronization code
based on lower-level primitives such as locks and condition variables. We
enable synchronization synthesis of finite-state concurrent programs composed of processes that may have local and shared variables, may be straight-line or branching programs, may be ongoing or terminating, and may have program-initialized or user-initialized variables. We also facilitate
expression of safety and liveness properties over both control and data
variables by proposing an extension of propositional computation tree logic.
Most program analyses, verification, debugging and synthesis methodologies target traditional correctness properties such as safety
and liveness. These techniques typically do not provide a quantitative
measure of the sensitivity of a computational system's behaviour to
unpredictability in the operating environment. We propose that the
core property of interest in reasoning in the presence of such uncertainty is robustness --- small perturbations to the operating environment do not change the system's observable behavior substantially. In well-established areas such as control theory, robustness has always been a fundamental concern; however, the
techniques and results therein are not directly applicable to computational systems with large amounts of discretized, discontinuous
behavior. Hence, robustness analysis of software programs used in heterogeneous settings necessitates development of new theoretical
frameworks and algorithms.
In the third part of this dissertation, we target robustness analysis of two
important classes of discrete systems --- string transducers and networked
systems of Mealy machines. For each system, we formally define robustness of the system with respect to a specific source of uncertainty. In particular, we
analyze the behaviour of transducers in the presence of input perturbations,
and the behaviour of networked systems in the presence of channel
perturbations. Our overall approach is automata-theoretic, and necessitates the use of specialized distance-tracking automata for tracking various
distance metrics between two strings. We present constructions for such
automata and use them to develop decision procedures based on reducing the problem of robustness verification of our systems to the problem of checking
the emptiness of certain automata. Thus, the system under consideration is robust if and only if the languages of particular automata are empty.Electrical and Computer Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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