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Computer

Issue 8 • Date Aug. 1992

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Displaying Results 1 - 5 of 5
  • Parallel programming using shared objects and broadcasting

    Page(s): 10 - 19
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    The two major design approaches taken to build distributed and parallel computer systems, multiprocessing and multicomputing, are discussed. A model that combines the best properties of both multiprocessor and multicomputer systems, easy-to-build hardware, and a conceptually simple programming model is presented. Using this model, a programmer defines and invokes operations on shared objects, the runtime system handles reads and writes on these objects, and the reliable broadcast layer implements indivisible updates to objects using the sequencing protocol. The resulting system is easy to program, easy to build, and has acceptable performance on problems with a moderate grain size in which reads are much more common than writes. Orca, a procedural language whose sequential constructs are roughly similar to languages like C or Modula 2 but which also supports parallel processes and shared objects and has been used to develop applications for the prototype system, is described.<> View full abstract»

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  • Model-based visual feedback control for a hand-eye coordinated robotic system

    Page(s): 21 - 31
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    The integration of a single camera into a robotic system to control the relative position and orientation between the robot's end-effector and a moving part in real time is discussed. Only monocular vision techniques are considered because of current limitations in the speed of computer vision analysis. The approach uses geometric models of both the part and the camera, as well as the extracted image features, to generate the appropriate robot control signals for tracking. Part and camera models are also used during the teaching stage to predict important image features that appear during task completion.<> View full abstract»

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  • Architectural support for goal management in flat concurrent Prolog

    Page(s): 34 - 47
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    A special-purpose architectural support that reduces the goal-management execution time in flat concurrent Prolog (FCP) is described. The architectural support consists of a dedicated goal-management unit that executes high-level goal-management operations concurrently with goal-reduction operations. The efficient execution of goal-management instructions is realized using a goal cache that stores recently spawned goals. It is shown that operations such as goal-switching, spawning, and halting are efficiently performed by changing their status in the goal cache. More complex operations, such as goal suspension and activation are decoupled from goal reduction by using two suspension tables and activation queues. Using an analytic performance model, it is shown that, for the systems development workload, which consists of large FCP programs, the overhead of software-implemented goal management is 50% of the program execution time. This is reduced up to 3% using the goal-management unit and the goal cache, resulting in a speedup of almost 2. The results are generalized for other workloads that exhibit different goal-management complexities.<> View full abstract»

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  • Flexible text display with Lector

    Page(s): 49 - 60
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    Lector, an X11 application for flexible text interaction, is described. Lector was originally devised as a simple, rapid formatter for the display of online text databases. It was then discovered that Lector exhibited useful capabilities for a wide range of text applications. The ways in which Lector distinguishes between content and tags in descriptively marked-up text and achieves flexible interaction are discussed. Its applications as a text previewer, database browser, code prettyprinter, and menu utility are also discussed.<> View full abstract»

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  • Demonstrational interfaces: A step beyond direct manipulation

    Page(s): 61 - 73
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    Demonstrational interfaces, interfaces that let the user perform actions on concrete example objects while constructing an abstract program, thus letting the user create parameterized procedures and objects without learning a programming language, are discussed. The motivations for and problems associated with demonstrational interfaces are presented. A survey of the various types of interfaces is also presented. Areas that would benefit from demonstrational technology, including general-purpose programming, visualization, macros for direct-manipulation interfaces, drawing packages, text editing and formatting, and user interface development environments, are discussed. Research issues involving demonstrational interfaces are reviewed.<> View full abstract»

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Computer, the flagship publication of the IEEE Computer Society, publishes highly acclaimed peer-reviewed articles written for and by professionals representing the full spectrum of computing technology from hardware to software and from current research to new applications.

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Editor-in-Chief
Ron Vetter
University of North Carolina
Wilmington