Catálogo de publicaciones - revistas

<jats:p>Concurrent logic languages are high-level programming languages for parallel and distributed systems that offer a wide range of both known and novel concurrent programming techniques. Being logic programming languages, they preserve many advantages of the abstract logic programming model, including the logical reading of programs and computations, the convenience of representing data structures with logical terms and manipulating them using unification, and the amenability to metaprogramming. Operationally, their model of computation consists of a dynamic set of concurrent processes, communicating by instantiating shared logical variables, synchronizing by waiting for variables to be instantiated, and making nondeterministic choices, possibly based on the availability of values of variables.</jats:p><jats:p>This paper surveys the family of concurrent logic programming languages within a uniform operational framework. It demonstrates the expressive power of even the simplest language in the family and investigates how varying the basic synchronization and control constructs affect the expressiveness and efficiency of the resulting languages.</jats:p><jats:p>In addition, the paper reports on techniques for sequential and parallel implementation of languages in this family, mentions their applications to date, and relates these languages to the abstract logic programming model, to the programming language PROLOG, and to other concurrent computational models and programming languages.</jats:p>

<jats:p>This paper considers the problem of providing security to statistical databases against disclosure of confidential information. Security-control methods suggested in the literature are classified into four general approaches: conceptual, query restriction, data perturbation, and output perturbation.</jats:p> <jats:p>Criteria for evaluating the performance of the various security-control methods are identified. Security-control methods that are based on each of the four approaches are discussed, together with their performance with respect to the identified evaluation criteria. A detailed comparative analysis of the most promising methods for protecting dynamic-online statistical databases is also presented.</jats:p> <jats:p>To date no single security-control method prevents both exact and partial disclosures. There are, however, a few perturbation-based methods that prevent exact disclosure and enable the database administrator to exercise "statistical disclosure control." Some of these methods, however introduce bias into query responses or suffer from the 0/1 query-set-size problem (i.e., partial disclosure is possible in case of null query set or a query set of size 1).</jats:p> <jats:p>We recommend directing future research efforts toward developing new methods that prevent exact disclosure and provide statistical-disclosure control, while at the same time do not suffer from the bias problem and the 0/1 query-set-size problem. Furthermore, efforts directed toward developing a bias-correction mechanism and solving the general problem of small query-set-size would help salvage a few of the current perturbation-based methods.</jats:p>

<jats:p>The best schemes for text compression use large models to help them predict which characters will come next. The actual next characters are coded with respect to the prediction, resulting in compression of information. Models are best formed adaptively, based on the text seen so far. This paper surveys successful strategies for adaptive modeling that are suitable for use in practical text compression systems.</jats:p> <jats:p>The strategies fall into three main classes: finite-context modeling, in which the last few characters are used to condition the probability distribution for the next one; finite-state modeling, in which the distribution is conditioned by the current state (and which subsumes finite-context modeling as an important special case); and dictionary modeling, in which strings of characters are replaced by pointers into an evolving dictionary. A comparison of different methods on the same sample texts is included, along with an analysis of future research directions.</jats:p>

<jats:p>The main problems associated with debugging concurrent programs are increased complexity, the "probe effect," nonrepeatability, and the lack of a synchronized global clock. The probe effect refers to the fact that any attempt to observe the behavior of a distributed system may change the behavior of that system. For some parallel programs, different executions with the same data will result in different results even without any attempt to observe the behavior. Even when the behavior can be observed, in many systems the lack of a synchronized global clock makes the results of the observation difficult to interpret. This paper discusses these and other problems related to debugging concurrent programs and presents a survey of current techniques used in debugging concurrent programs. Systems using three general techniques are described: traditional or breakpoint style debuggers, event monitoring systems, and static analysis systems. In addition, techniques for limiting, organizing, and displaying a large amount of data produced by the debugging systems are discussed.</jats:p>

<jats:p>This paper presents an overview of deterministic functional RAM chip testing. Instead of the traditional ad-hoc approach toward developing memory test algorithms, a hierarchy of functional faults and tests is presented, which is shown to cover all likely functional memory faults. This is done by presenting a novel way of categorizing the faults. All (possible) fault combinations are discussed. Requirements are put forward under which conditions a fault combination can be detected. Finally, memory test algorithms that satisfy the given requirements are presented.</jats:p>

<jats:p>Above all, it is vital to recognize that completely guaranteed behavior is impossible and that there are inherent risks in relying on computer systems in critical environments. The unforeseen consequences are often the most disastrous [Neumann 1986].</jats:p> <jats:p> Section 1 of this survey reviews the current state of the art of system reliability, safety, and fault tolerance. The emphasis is on the contribution of software to these areas. Section 2 reviews current approaches to software fault tolerance. It discusses why some of the assumptions underlying hardware fault tolerance do not hold for software. It argues that the current software fault tolerance techniques are more accurately thought of as delayed debugging than as fault tolerance. It goes on to show that in providing both backtracking and executable specifications, logic programming offers most of the tools currently used in software fault tolerance. Section 3 presents a generalization of the recovery block approach to software fault tolerance, called <jats:italic>resourceful systems</jats:italic> . Systems are resourceful if they are able to determine whether they have achieved their goals or, if not, to develop and carry out alternate plans. Section 3 develops an approach to designing resourceful systems based upon a functionally rich architecture and an explicit goal orientation. </jats:p>

<jats:p> Closed queueing networks are frequently used to model complex service systems such as production systems, communication systems, computer systems, and flexible manufacturing systems. When limitations are imposed on the queue sizes (i.e., finite queues), a phenomenon called <jats:italic>blocking</jats:italic> occurs. Queueing networks with blocking are, in general, difficult to treat. Exact closed form solutions have been reported only in a few special cases. Hence, most of the techniques that are used to analyze such queueing networks are in the form of approximations, numerical analysis, and simulation. In this paper, we give a systematic presentation of the literature related to closed queueing networks with finite queues. The results are significant for both researchers and practitioners. </jats:p>

<jats:p>For years computer-based stochastic simulation has been a commonly used tool in the performance evaluation of various systems. Unfortunately, the results of simulation studies quite often have little credibility, since they are presented without regard to their random nature and the need for proper statistical analysis of simulation output data.</jats:p> <jats:p>This paper discusses the main factors that can affect the accuracy of stochastic simulations designed to give insight into the steady-state behavior of queuing processes. The problems of correctly starting and stopping such simulation experiments to obtain the required statistical accuracy of the results are addressed. In this survey of possible solutions, the emphasis is put on possible applications in the sequential analysis of output data, which adaptively decides about continuing a simulation experiment until the required accuracy of results is reached. A suitable solution for deciding upon the starting point of a steady-state analysis and two techniques for obtaining the final simulation results to a required level of accuracy are presented, together with pseudocode implementations.</jats:p>

<jats:p>A federated database system (FDBS) is a collection of cooperating database systems that are autonomous and possibly heterogeneous. In this paper, we define a reference architecture for distributed database management systems from system and schema viewpoints and show how various FDBS architectures can be developed. We then define a methodology for developing one of the popular architectures of an FDBS. Finally, we discuss critical issues related to developing and operating an FDBS.</jats:p>

<jats:p>It is increasingly important for organizations to achieve additional coordination of diverse computerized operations. To do so, it is necessary to have database systems that can operate over a distributed network and can encompass a heterogeneous mix of computers, operating systems, communications links, and local database management systems. This paper outlines approaches to various aspects of heterogeneous distributed data management and describes the characteristics and architectures of seven existing heterogeneous distributed database systems developed for production use. The objective is a survey of the state of the art in systems targeted for production environments as opposed to research prototypes.</jats:p>