Catálogo de publicaciones - revistas

<jats:p> This survey covers rollback-recovery techniques that do not require special language constructs. In the first part of the survey we classify rollback-recovery protocols into <jats:italic>checkpoint-based</jats:italic> and <jats:italic>log-based.</jats:italic> <jats:italic>Checkpoint-based</jats:italic> protocols rely solely on checkpointing for system state restoration. Checkpointing can be coordinated, uncoordinated, or communication-induced. <jats:italic>Log-based</jats:italic> protocols combine checkpointing with logging of nondeterministic events, encoded in tuples called <jats:italic>determinants</jats:italic> . Depending on how determinants are logged, log-based protocols can be pessimistic, optimistic, or causal. Throughout the survey, we highlight the research issues that are at the core of rollback-recovery and present the solutions that currently address them. We also compare the performance of different rollback-recovery protocols with respect to a series of desirable properties and discuss the issues that arise in the practical implementations of these protocols. </jats:p>

<jats:p>The concept of an object-oriented database programming language (OODBPL) is appealing because it has the potential of combining the advantages of object orientation and database programming to yield a powerful and universal programming language design. A uniform and consistent combination of object orientation and database programming, however, is not straightforward. Since one of the main components of an object-oriented programming language is its type system, one of the first problems that arises during an OODBPL design is related to the development of a uniform, consistent, and theoretically sound type system that is sufficiently expressive to satisfy the combined needs of object orientation and database programming.The purpose of this article is to answer two questions: "What are the requirements that a modern type system for an object-oriented database programming language should satisfy?" and "Are there any type systems developed to-date that satisfy these requirements?". In order to answer the first question, we compile the set of requirements that an OODBPL type system should satisfy. We then use this set of requirements to evaluate more than 30 existing type systems. The result of this extensive analysis shows that while each of the requirements is satisfied by at least one type system, no type system satisfies all of them. It also enables identification of the mechanisms that lie behind the strengths and weaknesses of the current type systems.</jats:p>

<jats:p>An important goal of an operating system is to make computing and communication resources available in a fair and efficient way to the applications that will run on top of it. To achieve this result, the operating system implements a number of policies for allocating resources to, and sharing resources among applications, and it implements safety mechanisms to guard against misbehaving applications. However, for most of these allocation and sharing tasks, no single optimal policy exists. Different applications may prefer different operating system policies to achieve their goals in the best possible way. A<jats:italic>customizable</jats:italic>or<jats:italic>adaptable</jats:italic>operating system is an operating system that allows for flexible modification of important system policies. Over the past decade, a wide range of approaches for achieving customizability has been explored in the operating systems research community. In this survey, an overview of these approaches, structured around a taxonomy, is presented.</jats:p>

<jats:p> The unabated growth and increasing significance of the World Wide Web has resulted in a flurry of research activity to improve its capacity for serving information more effectively. But at the heart of these efforts lie implicit assumptions about "quality" and "usefulness" of Web resources and services. This observation points towards measurements and models that quantify various attributes of web sites. The science of measuring all aspects of information, especially its storage and retrieval or <jats:italic>informetrics</jats:italic> has interested information scientists for decades before the existence of the Web. Is Web informetrics any different, or is it just an application of classical informetrics to a new medium? In this article, we examine this issue by classifying and discussing a wide ranging set of Web metrics. We present the origins, measurement functions, formulations and comparisons of well-known Web metrics for quantifying <jats:italic>Web graph properties</jats:italic> , <jats:italic>Web page significance</jats:italic> , <jats:italic>Web page similarity</jats:italic> , <jats:italic>search and retrieval</jats:italic> , <jats:italic>usage characterization</jats:italic> and <jats:italic>information theoretic properties</jats:italic> . We also discuss how these metrics can be applied for improving Web information access and use. </jats:p>

<jats:p>In this tutorial, selected topics of cryptology and of computational complexity theory are presented. We give a brief overview of the history and the foundations of classical cryptography, and then move on to modern public-key cryptography. Particular attention is paid to cryptographic protocols and the problem of constructing key components of protocols such as one-way functions. A function is one-way if it is easy to compute, but hard to invert. We discuss the notion of one-way functions both in a cryptographic and in a complexity-theoretic setting. We also consider interactive proof systems and present some interesting zero-knowledge protocols. In a zero-knowledge protocol, one party can convince the other party of knowing some secret information without disclosing any bit of this information. Motivated by these protocols, we survey some complexity-theoretic results on interactive proof systems and related complexity classes.</jats:p>

<jats:p>This article is a survey of research areas in which motion plays a pivotal role. The aim of the article is to review current approaches to modeling motion together with related data structures and algorithms, and to summarize the challenges that lie ahead in producing a more unified theory of motion representation that would be useful across several disciplines.</jats:p>

<jats:p> For many years, there has been considerable debate about whether the IT revolution was paying off in higher productivity. Studies in the 1980s found no connection between IT investment and productivity in the U.S. economy, a situation referred to as the <jats:italic>productivity paradox</jats:italic> . Since then, a decade of studies at the firm and country level has consistently shown that the impact of IT investment on labor productivity and economic growth is significant and positive. This article critically reviews the published research, more than 50 articles, on computers and productivity. It develops a general framework for classifying the research, which facilitates identifying what we know, how well we know it, and what we do not know. The framework enables us to systematically organize, synthesize, and evaluate the empirical evidence and to identify both limitations in existing research and data and substantive areas for future research.The review concludes that the productivity paradox as first formulated has been effectively refuted. At both the firm and the country level, greater investment in IT is associated with greater productivity growth. At the firm level, the review further concludes that the wide range of performance of IT investments among different organizations can be explained by complementary investments in organizational capital such as decentralized decision-making systems, job training, and business process redesign. IT is not simply a tool for automating existing processes, but is more importantly an enabler of organizational changes that can lead to additional productivity gains.In mid-2000, IT capital investment began to fall sharply due to slowing economic growth, the collapse of many Internet-related firms, and reductions in IT spending by other firms facing fewer competitive pressures from Internet firms. This reduction in IT investment has had devastating effects on the IT-producing sector, and may lead to slower economic and productivity growth in the U.S. economy. While the turmoil in the technology sector has been unsettling to investors and executives alike, this review shows that it should not overshadow the fundamental changes that have occurred as a result of firms' investments in IT. Notwithstanding the demise of many Internet-related companies, the returns to IT investment are real, and innovative companies continue to lead the way. </jats:p>

<jats:p>Hardware multithreading is becoming a generally applied technique in the next generation of microprocessors. Several multithreaded processors are announced by industry or already into production in the areas of high-performance microprocessors, media, and network processors.A multithreaded processor is able to pursue two or more threads of control in parallel within the processor pipeline. The contexts of two or more threads of control are often stored in separate on-chip register sets. Unused instruction slots, which arise from latencies during the pipelined execution of single-threaded programs by a contemporary microprocessor, are filled by instructions of other threads within a multithreaded processor. The execution units are multiplexed between the thread contexts that are loaded in the register sets.Underutilization of a superscalar processor due to missing instruction-level parallelism can be overcome by simultaneous multithreading, where a processor can issue multiple instructions from multiple threads each cycle. Simultaneous multithreaded processors combine the multithreading technique with a wide-issue superscalar processor to utilize a larger part of the issue bandwidth by issuing instructions from different threads simultaneously.Explicit multithreaded processors are multithreaded processors that apply processes or operating system threads in their hardware thread slots. These processors optimize the throughput of multiprogramming workloads rather than single-thread performance. We distinguish these processors from implicit multithreaded processors that utilize thread-level speculation by speculatively executing compiler- or machine-generated threads of control that are part of a single sequential program.This survey paper explains and classifies the explicit multithreading techniques in research and in commercial microprocessors.</jats:p>

<jats:p>Laser scanning range sensors are widely used for high-precision, high-density three-dimensional (3D) reconstruction and inspection of the surface of physical objects. The process typically involves planning a set of views, physically altering the relative object-sensor pose, taking scans, registering the acquired geometric data in a common coordinate frame of reference, and finally integrating range images into a nonredundant model. Efficiencies could be achieved by automating or semiautomating this process. While challenges remain, there are adequate solutions to semiautomate the scan-register-integrate tasks. On the other hand, view planning remains an open problem---that is, the task of finding a suitably small set of sensor poses and configurations for specified reconstruction or inspection goals. This paper surveys and compares view planning techniques for automated 3D object reconstruction and inspection by means of active, triangulation-based range sensors.</jats:p>

<jats:p>Software systems have been using "just-in-time" compilation (JIT) techniques since the 1960s. Broadly, JIT compilation includes any translation performed dynamically, after a program has started execution. We examine the motivation behind JIT compilation and constraints imposed on JIT compilation systems, and present a classification scheme for such systems. This classification emerges as we survey forty years of JIT work, from 1960--2000.</jats:p>