Computer graphics comes of age: an interview with Andries Van Dam
Andries van Dam describes major advances in computer graphics over the past 25 years and discusses future directions.
Systems and Networking
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Audit trail compaction for database recovery
Total elapsed recovery time from disk-based database corruption can be shortened by reprocessing the audit trail off-line and thereby avoiding excessive resource utilization penalties. Using a bit map, the audit trail is compacted by eliminating irrelevant or superseded records. The compacted trail is then partitioned, and the partitions are processed in parallel.
Where can you find a solid, forthright overview of the computer systems and management behind airline reservations? NASA's space shuttle? Or any of the multitude of other large computer systems that support important projects or national activities? It's hard, sometimes impossible: partly because the people who worked on such systems often do not have the time to write about their experiences: and partly because many professional journalists who interview these people do not have the technical background to ferret out answers to the fundamental design questions addressed in these systems.
File organization: implementation of a method guaranteeing retrieval in one access
A new file organization method that guarantees retrieval of any record in one access is tested on two existing files, producing empirical results that compare favorably with theoretical predictions. The description of the method includes the algorithms used for implementing the required hashing and signature functions.
Faster methods for random sampling
Several new methods are presented for selecting n records at random without replacement from a file containing N records. Each algorithm selects the records for the sample in a sequential manner—in the same order the records appear in the file. The algorithms are online in that the records for the sample are selected iteratively with no preprocessing. The algorithms require a constant amount of space and are short and easy to implement. The main result of this paper is the design and analysis of Algorithm D, which does the sampling in O(n) time, on the average; roughly n uniform random variates are generated, and approximately n exponentiation operations (of the form ab, for real numbers a and b) are performed during the sampling. This solves an open problem in the literature. CPU timings on a large mainframe computer indicate that Algorithm D is significantly faster than the sampling algorithms in use today.
Efficient algorithms to globally balance a binary search tree
A binary search tree can be globally balanced by readjustment of pointers or with a sorting process in O(n) time, n being the total number of nodes. This paper presents three global balancing algorithms, one of which uses folding with the other two adopting parallel procedures. These algorithms show improvement in time efficiency over some sequential algorithms [1, 2, 7] when applied to large binary search trees. A comparison of various algorithms is presented.
A large font virtual terminal interface: a software prosthesis for the visually impaired
A large font software interface running under UNIX1 is of great assistance to the severely visually impaired in the interactive use of computers. The interface, which functions as a virtual terminal as far as other processes are concerned, displays all characters (both user and system generated) at user-selectable degrees of magnification, yet is compatible with any standard CRT/keyboard terminal.
An assessment of the prototyping approach to information systems development
A two-phased research project comparing the prototyping approach with the more traditional life cycle approach finds that prototyping facilitates communication between users and designers during the design process. However, the findings also indicate that designers who used prototyping experienced difficulties in managing and controlling the design process.
From Washington: NSF takes the initiative
The National Science Foundation's Advisory Committee for Advanced Scientific Computing Resources was formed to provide leadership for large-scale scientific computing throughout the United States. Consisting of 15 members representing universities, industry, and national laboratories, the Committee held its first meeting in January 1984. A summary of the meeting issued by Chairman Neal F. Lane of Rice University makes the following points.
Talking to UNIX in English: an overview of UC
UC is a natural language help facility which advises users in using the UNIX operating system. Users can query UC about how to do things, command names and formats, online definitions of UNIX or general operating systems terminology, and debugging problems in using commands. UC is comprised of the following components: a language analyzer and generator, a context and memory model, an experimental common-sense planner, highly extensible knowledge bases on both the UNIX domain and the English language, a goal analysis component, and a system for acquisition of new knowledge through instruction in English. The language interface of UC is based on a “phrasal analysis” approach which integrates semantic, grammatical and other types of information. In addition, it includes capabilities for ellipsis resolution and reference disambiguation.
Laser optical disk: the coming revolution in on-line storage
Commercially available only recently, the optical disk drive uses a laser beam to burn impressions onto a plastic disk. Employing a highly focused beam rather than a diffuse magnetic field to write, the laser optical disk drive yields storage densities up to 10 times those of magnetic disks.
Programming pearls: graphic output
In previous columns we've studied the innards of programs. In this column we'll take a broader view of the programmer's task and consider the kind of output a program should produce. We'll focus on a single problem: once a system has produced detailed output, how can it summarize the trends in the mountain of data?
The answer to that question depends heavily on both the data and the taste of the reader; paragraphs of text and tables of numbers often provide fine summaries. This column, however, will concetrate on graphical representations of data, which allow the powerful human vision system to understand data. A decade ago programmers could offer the excuse that they were limited to crude line printer graphics, but technology has changed that. Many large installations now have laser printers, and graphics printers for home computers sell for a few hundred dollars. This column is about ways that programmers can use the technology to deliver more useful (and more graphic) output.
Anomalies in parallel branch-and-bound algorithms
We consider the effects of parallelizing branch-and-bound algorithms by expanding several live nodes simultaneously. It is shown that it is quite possible for a parallel branch-and-bound algorithm using n2 processors to take more time than one using n1 processors, even though n1 < n2. Furthermore, it is also possible to achieve speed-ups that are in excess of the ratio n2/n1. Experimental results with the 0/1-Knapsack and Traveling Salesman problems are also presented.
Updating a database in an unsafe environment
Normally, when an application makes use of a database, considerable resources are invested in maintaining the integrity of that database. However, in situations where use of a database may be desirable even though the normal level of resources is unavailable, a simple technique using a partitioned data file protects the database if immediate transaction recording is not essential.
Computer matching: should it be banned?
Since discovering the technique of computer matching several years ago, government managers have been invoking this computer tool in the attempt to root out waste and fraud in their programs. Is computer matching an indispensable tool for government administrators? Or a trampling on individual rights? In the following articles, two experts debate the pros and cons.
A virtual memory system for picture processing
A virtual memory system designed specifically for picture processing, Raster Handler 2 provides programs with efficient access to pixels. It features square partition of images, imbalanced allocation of frames, and nondemand page replacement. RH2 is implemented in software and incorporates a prepaging algorithm designed specifically for picture processing.
An algorithm for optimized Boolean evaluation in information management systems
In cases where simple data validation techniques are inadequate and optimization policies relatively complex (e.g., in health and medical systems), a Boolean optimization algorithm can be used to report errors accurately and unambiguously. The algorithm is presented in the context of a data-validating software module that uses an LR(1)-parser. The algorithm's precision makes it of potential use for the retrieval of records that nearly satisfy a query.
Accommodating uncertainty in software design
Recognition that most software is domain dependent (DD) is extremely important because the most commonly used software life-cycle models are not adequate for DD software. The nature of DD software, and the need to manage its life cycle effectively, calls for a new approach to software design and the implementation of software development environments.
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