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Research and Advances

A locally adaptive data compression scheme

A data compression scheme that exploits locality of reference, such as occurs when words are used frequently over short intervals and then fall into long periods of disuse, is described. The scheme is based on a simple heuristic for self-organizing sequential search and on variable-length encodings of integers. We prove that it never performs much worse than Huffman coding and can perform substantially better; experiments on real files show that its performance is usually quite close to that of Huffman coding. Our scheme has many implementation advantages: it is simple, allows fast encoding and decoding, and requires only one pass over the data to be compressed (static Huffman coding takes two passes).
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Research and Advances

Andrew: a distributed personal computing environment

The Information Technology Center (ITC), a collaborative effort between IBM and Carnegie-Mellon University, is in the process of creating Andrew, a prototype computing and communication system for universities. This article traces the origins of Andrew, discusses its goals and strategies, and gives an overview of the current status of its implementation and usage.
Research and Advances

An empirical study of the impact of user involvement on system usage and information satisfaction

"User involvement" in information system development is generally considered an important mechanism for improving system quality and ensuring successful system implementation. The common assumption that user involvement leads to system usage and/or information satisfaction is examined in a survey of 200 production managers. Alternative models exploring the causal ordering of the three variables are developed and tested via path analysis. The results demonstrate that user involvement in the development of information systems will enhance both system usage and the user's satisfaction with the system. Further, the study provides evidence that the user's satisfaction with the system will lead to greater system usage.
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Research and Advances

Organizational power and the information services department: a reexamination

In a recent application of the theory of strategic contingencies in three large multinational firms, Lucas found that information services departments were perceived by others as having low levels of power and influence and suggested a variety of reasons for the results. This note continues the application of the theory of strategic contingencies to the information services department by describing a study of intraorganizational power that uses basically the same procedures as the Lucas study and obtains similar results. In an effort to stimulate future power-related research in the information systems area, this note concludes by suggesting several reasons, beyond those given by Lucas, for the levels of power attributed to information services departments.
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Research and Advances

Complexity and parallel processing: an interview with Richard Karp

In the following interview, which took place at ACM 85 in Denver, Karp discusses the relation of his work to leading-edge computing topics like parallel processing and artificial intelligence. Tracing his experience as a pioneer in highly theoretical computer science, Karp describes how the decision to go against established wisdom led to the work for which he is best known and how a colleague's findings led him to see links between two previously unrelated areas. Throughout, he stresses the exchange of ideas with colleagues that helped yield fundamental insights.
Research and Advances

Dynamic initial allocation and local reallocation procedures for multiple stacks

Two new procedures for manipulating multiple stacks which share sequential memory locations are discussed. The first is the dynamic initial allocation procedure in which each stack is allocated as its first element arrives rather than having every stack preallocated at the very beginning of the entire process. The second is the local reallocation procedure; in this scheme, when a stack overflows, only its neighboring stacks, rather than the entire memory area, are reorganized provided that a certain condition is satisfied. The results of simulation appear to suggest that these new approaches improve the operational performance in many applications. With appropriate modifications, these concepts may also be applied to any other type of multiple linear lists (e.g., multiple queues) sharing sequential memory locations.
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Research and Advances

Structured tools and conditional logic: an empirical investigation

Prior research has identified two psychological processes that appear to be used by programmers when they perform design and coding tasks: (a) taxonomizing—identifying the conditions that evoke particular actions; and (b) sequencing—converting the taxa into a linear sequence of program code. Three structured tools—structured English, decision tables, and decision trees—were investigated in a laboratory experiment to determine how they facilitated these two processes. When taxonomizing had to be undertaken, structured English outperformed decision tables, and decision trees outperformed structured English. When sequencing had to be undertaken, decision trees and structured English outperformed decision tables, but decision trees and structured English evoked the same level of performance.
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Research and Advances

Understanding the effectiveness of computer graphics for decision support: a cumulative experimental approach

A total of 840 junior and senior-level undergraduate business students particpated in three experiments that compared computer-generated graphical forms of data presentation to traditional tabular reports. The first experiment compared tables and bar charts for their effects on readability, interpretation accuracy, and decision making. No differences in interpretation accuracy or decision quality were observed for the two groups, although tabular reports were rated as "easier to read and understand" than graphical reports. The second experiment compared line plots to tables for their effects on interpretation accuracy and decision quality. Subjects with graphical reports outperformed those with tables. There were no meaningful differences in interpretation accuracy across treatment groups. The third experiment compared graphical and tabular reports for their ability to convey a "message" to the reader. Only in situations in which a vast amount of information was presented and relatively simple impressions were to be made, did subjects given graphs outperform those using tables. This program of cumulative experiments indicates that generalized claims of superiority of graphic presentation are unsupported, at least for decision-related activities. In fact, the experiments suggest that the effectiveness of the data display format is largely a function of the characteristics of the task at hand, and that impressions gleaned from "one shot" studies of the effectiveness of the use of graphs may be nothing more than situationally dependent artifacts.
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Research and Advances

Data quality and due process in large interorganizational record systems

As societies have become more dependent on information systems to conduct and record transactions between organizations and individuals, interorganizational computer systems have become a widely used method of coordinating the actions of independent organizations. This article examines the quality of data in one important interorganizational system—the criminal-record system of the United States.

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