Showing papers in "ACM Computing Surveys in 1984"

The Quadtree and Related Hierarchical Data Structures

Abstract: Apercu sur les quadarbres et les structures de donnees hierarchiques. Elles sont basees sur le principe de decomposition recursive. L'accentuation est mise sur la representation de donnees dans les applications de traitement d'images, d'infographie, les systemes d'informations geographiques et la robotique. On examine en detail un certain nombre d'operations dans lesquelles de telles structures de donnees trouvent leur utilisation

Logic and Databases: A Deductive Approach

Abstract: The purpose of this paper is to show that logic provides a convenient formalism for studying classical database problems. There are two main parts to the paper, devoted respectively to conventional databases and deductive databases. In the first part, we focus on query languages, integrity modeling and maintenance, query optimization, and data dependencies. The second part deals mainly with the representation and manipulation of deduced facts and incomplete information. Categories and Subject Descriptors: H.2.1 [Database Management]: Logical Design— data models; H.2.3 [Database Management]: Languages— query languages; H.2.4 [Database Management]: Systems— query processing General Terms: Deductive Databases, Indefinite Data, Logic and Databases, Null Values, Relational Databases

Query Optimization in Database Systems

Abstract: Efficient methods of processing unanticipated queries are a crucial prerequisite for the success of generalized database management systems. A wide variety of approaches to improve the performance of query evaluation algorithms have been proposed: logic-based and semantic transformations, fast implementations of basic operations, and combinatorial or heuristic algorithms for generating alternative access plans and choosing among them. These methods are presented in the framework of a general query evaluation procedure using the relational calculus representation of queries. In addition, nonstandard query optimization issues such as higher level query evaluation, query optimization in distributed databases, and use of database machines are addressed. The focus, however, is on query optimization in centralized database systems.

Response time and display rate in human performance with computers

Abstract: The pace of human-computer interaction is an important issue to computer scientists and computer users alike. Experimental results have begun to shed some light on this complex, controversml, and vital subject. This paper revmws the theory and reports on experimental results concerning display rates, response time expectations and attitudes, user productivity, and variability. The decomposition of concerns and tasks helps to clarify the issues, but substanhal effort remains before a predictive model can emerge. In general, the results indicate that frequent users prefer response times of less than a second for most tasks, and that productwlty does increase as response time decreases. However, error rates increase with too short or too long a response time. Users pick up the pace of the system, but the profile of commands may change with the speed of the system

Distributed query processing

Abstract: On presente plusieurs techniques d'optimisation des questions au sein d'un reseau de bases de donnees. Les caracteristiques d'un algorithme integrant ces techniques sont enoncees

Multiple-access protocols and time-constrained communication

Abstract: During the past ten years, the field of multiple-access communication has developed into a major area of both practical and theoretical interest within the field of computer communications. The multiple-access problem arises from the necessity of sharing a single communication channel among a community of distributed users. The distributed algorithm used by the stations to share the channel is known as the multiple-access protocol. In this paper we examine the multiple-access problem and various approaches to its resolution.In this survey we first define the multiple-access problem and then present the underlying issues and difficulties in achieving multiple-access communication. A taxonomy for multiple-access protocols is then developed in order to characterize common approaches and to provide a framework within which these protocols can be compared and contrasted. Different proposed protocols are then described and discussed, and aspects of their performance are examined. The use of multiple-access protocols for "real- time" or "time-constrained" communication applications, such as voice transmission, is examined next. Issues in time-constrained communication are identified, and recent work in the design of time-constrained multiple-access protocols is surveyed.

A taxonomy of parallel sorting

Abstract: In this paper, we propose a taxonomy of parallel sorting that includes a broad range of array and file sorting algorithms. We analyze the evolution of research on parallel sorting, from the earliest sorting networks to the shared memory algorithms and the VLSI sorters. In the context of sorting networks, we describe two fundamental parallel merging schemes the odd-even and the bitonic merge. Sorting algorithms have been derived from these merging algorithms for parallel computers where processors communicate through interconnection networks such as the perfect shuffle, the mesh and a number of other sparse networks. After describing the network sorting algorithms, we show that, with a shared memory model of parallel computation, faster algorithms have been derived from parallel enumeration sorting schemes, where keys are first ranked and then rearranged according to their rank. Parallel sorting algorithms are evaluated according to a number of criteria, related not only to their time complexity, but also to their feasibility from a computer architecture point of view. We show that in addition to their attractive communication schemes, network sorting algorithms have non-adaptive schedules that make them suitable for implementation. In particular, they are easily generalized to block-sorting algorithms, that utilize limited parallelism to solve large sorting problems. We also address the problem of sorting large mass-storage files in parallel, using modified disk devices or intelligent bubble memories. Finally, the newer area of VLSI sorting is mentioned as an active and promising direction of research on parallel sorting.

File servers for network-based distributed systems

Abstract: Le «file server» est un service assurant l'interface entre l'utilisateur et le fichier qu'il interroge, dans le cadre d'un reseau d'information. Diverses caracteristiques des «file servers» sont decrites a partir d'une etude de quelques serveurs experimentaux

Parallel graph algorithms

Abstract: Algorithms and data structures developed to solve graph problems on parallel computers are surveyed. The problems discussed relate to searching graphs and finding connected components, maximal chques, maximum cardinahty matchings, mimmum spanning trees, shortest paths, and travehng salesman tours. The algorithms are based on a number of models of parallel computation, including systohc arrays, assoclatwe processors, array processors, and mulhple CPU computers. The most popular model is a direct extension of the standard RAM model of sequential computation. It may not, however, be the best basis for the study of parallel algorithms. More emphasis has been focused recently on communications issues in the analysis of the complexity of parallel algorithms; thus parallel models are coming to be more complementary to implementable architectures. Most algorithms use relatwely simple data structures, such as the adjacency matrix and adjacency hsts, although a few algorithms using linked hsts, heaps, and trees are also discussed.

Highly available systems for database applications

Abstract: As users entrust more and more of their applications to computer systems, the need for systems that are continuously operational (24 hours per day) has become even greater. This paper presents a survey and analysis of representative architectures and techniques that have been developed for constructing highly available systems for database applications. It then proposes a design of a distributed software subsystem that can serve as a unified framework for constructing database application systems that meet various requirements for high availability.