A complete set of algebraic laws is given for Dijkstra's nondeterministic sequential programming language. Iteration and recursion are explained in terms of Scott's domain theory as fixed points of continuous functionals. A calculus analogous to weakest preconditions is suggested as an aid to deriving programs from their specifications.
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One of the primary effects of software abstraction has been to further the notion of computer programs as objects rather than moving programming closer to the problem being solved. Knowledge abstraction, however, allows software to take a significant step toward the problem domain.
Recently developed word processing software can correctly format the cursive, interacting letters of the Arabic script. Moreover, new layout procedures can automatically intermix right-to-left Arabic writing with left-to-right text in European or other languages.
Adjacency detection using quadcodes
A method is presented for determining whether two given regions are adjacent, and for finding all the neighbors of different sizes for a given region. Regions are defined as elementary squares of any size. In a companion paper [2], we introduce the quadcode and discuss its use in representing geometric concepts in the coded image, such as location, distance, and adjacency. In this paper we give a further discussion of adjacency in terms of quadcodes. Gargantini [1] discussed adjacency detection using linear quadtrees. Her discussion was applied to pixels, and a procedure was given to find a pixel's southern neighbor only. This paper considers elementary squares of any size, and gives procedures for both aspects of the problem: for determining whether two given regions are adjacent, and for finding all the neighbors of different sizes for a given region.
The quadcode and its arithmetic
The quadcode is a hierarchical data structure for describing digital images. It has the following properties: (1) straightforward representation of dimension, size, and the relationship between an image and its subsets; (2) explicit description of geometric properties, such as location, distance, and adjacency; and (3) ease of conversion from and to raster representation. The quadcode has applications to computer graphics and image processing because of its ability to focus on selected subsets of the data and to allow utilization of multiple resolutions in different parts of the image. A related approach is the quadtree. Samet recently presented a thorough survey of the literature in that field [7]. Gargantini [2] and Abel and Smith [1] presented linear quadtrees and linear locational keys that are efficient labeling techniques for quadtrees. In those papers the geometric concepts of the image are discussed by using the tree as an interpretive medium, and the approaches and procedures are based on traversal of the nodes in the tree. In this paper we present the quadcode system, which is a direct description of the image, and discuss the geometric concepts in terms of the coded images themselves.
Spanish is a language with very precise and regular orthographic rules. A syllabication algorithm strictly based on syntactic analysis, not requiring any semantic knowledge, is presented and further extended to include hyphenation. Algorithms are presented as pattern matching schemata, and efficient implementations are considered.
The tea-leaf reader algorithm: an efficient implementation of CRC-16 and CRC-32
The tea-leaf reader CRC algorithms are error-detection algorithms that use a look-ahead table to increase execution speed.
Relationships between selected organizational factors and systems development
Three organizational variables influence the quality of the system development process: available resources (both human and financial), external influences on the development process, and the project team's exposure to information systems. Public information and interviews with systems managers from 28 large private firms yielded data about the organizational variables. Systems project group members completed questionnaires concerning the system development process. The results indicate that human resources affect the development process positively, but increased financial resources are related to team disagreement. The degree of external influence on the system development effort needs to be carefully monitored and controlled. Systems exposure in the firm allows an increase in the degree of awareness among project group members about the different problems encountered by users and systems staff.
Power over users: its exercise by system professionals
Analysis and awareness of the types of power that IS professionals exercise over users can improve the productivity of both parties.
Systems analysis: a systemic analysis of a conceptual model
Adopting an appropriate model for systems analysis, by avoiding a narrow focus on the requirements specification and increasing the use of the systems analyst's knowledge base, may lead to better software development and improved system life-cycle management.
Electronic markets and electronic hierarchies
By reducing the costs of coordination, information technology will lead to an overall shift toward proportionately more use of markets—rather than hierarchies—to coordinate economic activity.
An analysis of variance (ANOVA) model is developed for determining the existence of significant differences among strategies employing heuristics. Use of the model is illustrated in an application involving capacity assignment for networks utilizing the dynamic hierarchy architecture, in which the apex node is reassigned in response to changing environments. The importance of the model lies in the structure provided to the evaluation of heuristics, a major need in the assessment of benefits of artificial-intelligence applications. A nested three-factor design with fixed and random effects provides a numerical example of the model.
An empirical validation of software cost estimation models
Practitioners have expressed concern over their inability to accurately estimate costs associated with software development. This concern has become even more pressing as costs associated with development continue to increase. As a result, considerable research attention is now directed at gaining a better understanding of the software-development process as well as constructing and evaluating software cost estimating tools. This paper evaluates four of the most popular algorithmic models used to estimate software costs (SLIM, COCOMO, Function Points, and ESTIMACS). Data on 15 large completed business data-processing projects were collected and used to test the accuracy of the models' ex post effort estimation. One important result was that Albrecht's Function Points effort estimation model was validated by the independent data provided in this study [3]. The models not developed in business data-processing environments showed significant need for calibration. As models of the software-development process, all of the models tested failed to sufficiently reflect the underlying factors affecting productivity. Further research will be required to develop understanding in this area.
Taking “computer literacy” literally
Computer literacy implies an analogy between computer-related skills and linguistic literacy that has not been seriously explored. Recent studies of linguistic literacy can illuminate the definition of computer literacy and can suggest new ways of teaching it.
This report summarizes the activities of the Computing Sciences Accreditation Board from its inception in 1984 through its first accreditation cycle completed in June 1986. The major activities during this period were directed at developing the CSAB structure necessary to carry out the accreditation process, and at conducting the first round of accreditation visits and actions.
Distribution of mathematical software via electronic mail
A large collection of public-domain mathematical software is now available via electronic mail. Messages sent to "netlib@anl-mcs" (on the Arpanet/CSNET) or to "research!netlib" (on the UNIX® network) wake up a server that distributes items from the collection. The one-line message "send index" causes a library catalog to be sent by return mail.
Intelligent information-sharing systems
The Information Lens system is a prototype intelligent information-sharing system that is designed to include not only good user interfaces for supporting the problem-solving activity of individuals, but also good organizational interfaces for supporting the problem-solving activities of groups.
A software architecture for supporting the exchange of electronic manuscripts
As electronic-manuscript exchange becomes more prevalent, problems arise in translating among the wide variety of electronic representations. The optimum solution is a system that can support both the use and the creation of translation tools.
A mathematically focused curriculum for computer science
A curriculum that is flexible enough to suit all students studying computer science, and that reintegrates the theoretical aspects of the field along with more practical or vocational aspects, is proposed.
Case study: IBM’s system/360-370 architecture
The architecture of IBM's System/360-370 series of compatible processors is one of the most durable artifacts of the computer age. Through two major revisions of the product line and 23 years of technological change, it has remained a viable and versatile interface between machine and user.
Attributes of the performance of central processing units: a relative performance prediction model
Using readily available data on CPU characteristics—main memory size, cache memory size, number of channels, and machine cycle time—it is possible to predict relative CPU performance for a wide range of machines. Statistical analyses indicate that these characteristics explain virtually all the variance in relative performance.
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Get InvolvedCommunications of the ACM (CACM) is now a fully Open Access publication.
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