Thomas G. Moher

Learning and Building Together in an Immersive Virtual World

This paper describes the design, evaluation, and lessons learned from a project involving the implementation of an immersive virtual environment for children called NICE (Narrative-based, Immersive, Constructionist/Collaborative Environments). The goal of the NICE project was to construct a testbed for the exploration of virtual reality as a learning medium within the context of the primary educational reform themes of the past three decades. With a focus on informal education and domains with social content, NICE embraces the constructivist approach to learning, collaboration, and narrative development, and is designed to utilize the strengths of virtual reality: a combination of immersion, telepresence, immediate visual feedback, and interactivity. Based on our experiences with a broad range of users, the paper discusses both the successes and limitations of NICE and concludes with recommendations for research directions in the application of immersive VR technologies to childrens learning.

Design of the opportunistic garbage collector

The Opportunistic Garbage Collector (OGC) is a generational garbage collector for stock hardware and operating systems. While incorporating important features of previous systems, the OGC includes several innovations. A new bucket brigade heap organization supports advancement thresholds between one and two scavenges, using only two or three spaces per generation, and without requiring per-object counts. Opportunistic scavenging decouples scavenging from the filling of available memory, in order to hide potentially disruptive scavenge pauses and improve efficiency. Card marking efficiently records which small areas of the heap may contain pointers into younger generations, and is supported by a refinement of the crossing map technique, to enable scanning of arbitrary cards.

Effective “static-graph” reorganization to improve locality in garbage-collected systems

Several researchers have attempted to improve locality in garbage-collected heaps by changing the traversal algorithm used by a copying garbage collector. Unfortunately, these studies met with small success. We hypothesized that the disappointing results of these previous studies were due to two flaws in the traversal algorithms tested. They failed to group data structures in a manner reflecting their hierarchical organization, and more importantly, they ignored the dkastrous grouping effects caused by reaching data structures from a linear traversal of hash tables (i.e., in pseudo-random order). To test this hypothesis, we modified the garbage collector of a Lisp system (specifically, the Scheme-48 system) to avoid both problems in reorganizing the system heap image. We implemented our “hierarchical decomposition” algorithm (a cousin of Moon’s “approximately depth-fiist” algorithm) that is quite efficient on stock hardware. We aleo changed the collector to traverse global variable bindings in the order of their creation rather than in the memory order imposed by hash tables. The effects of these changes confirm our hypothesis. Some improvement comes from the basic traversal algorithm, and a greater effect results from the special treatment of hash tables. Initial page faults are reduced significantly and repeated page faults are reduced tremendously (by roughly an order of magnitude). In addition, improved measures of static locality (such as the percentage of on-page pointers) indicate that heap data can be cheaply and effectively compressed, and this may allow more effective paging and prefetching strategies; we suggest a level of “compressed in-RAM storage”, with price and performance between those of RAM and disk. These results call for a reinterpretation of previous studies, and for further studies of static-graph traversal techniques. They reduce the attractiveness of the exotic hardware needed for dynamically reorganizing objects within pages, and show that good locality can easily be achieved by straightforward and efficient techniques on stock hardware. Permission to copy without fee all or part of this material is granted provided that the copies ere not mede or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. @ 1991 ACM 0-89791-428-7/91/0005/01 77...

The NICE project: learning together in a virtual world

1.50 Proceedings of the ACM SIGPLAN ‘91 Conference on Programming Language Design and Implementation. Toronto, Ontario, Canada, June 26-28, 1991.

PROVIDE: a process visualization and debugging environment

This paper describes the NICE project, an immersive learning environment for children implemented in the CAVE and related multi-user virtual reality (VR) technologies. The NICE project provides an engaging setting where children construct and cultivate simple virtual ecosystems, collaborate via networks with other remotely-located children, and create stories from their interactions in the real and virtual world.

Some strategies of reuse in an object-oriented programming environment

The author introduces PROVIDE, a source-level process visualization and debugging environment currently under development at the University of Illinois at Chicago. PROVIDE is a modern coding and debugging environment that is designed to allow the user to configure interaction at a desired level of abstraction. It emphasizes the use of interactive computer graphics for the illustration of program execution, with special attention to the requirements of program debugging. The major features of PROVIDE are presented, especially the concepts of deferred-binding program animation, which allows users to interactively change the depiction of program execution during the debugging task, and process history consistency maintenance, which guarantees a consistent (automatically updated) record of program execution in the face of changes to program instructions and run-time data values. The current PROVIDE prototype is implemented on Macintosh workstations networked to a VAX 11/780 running 4.2 BSD Unix. >

NICE: combining constructionism, narrative and collaboration in a virtual learning environment

In a single-subject study of a software developer working in an object-oriented programming environment, we found evidence of a development style characterized by pervasive software reuse. The subject employed regular strategies for template selection and coding in her work, and avoided techniques requiring deep understanding of code details or symbolic execution whenever possible. Within the limits of the design of the study, the subjects performance is related to attributes of object-oriented programming and our interpretation of the mature mental model with which she approached her task.

The Round Earth Project-collaborative VR for conceptual learning

Maria Roussos, Andrew E. Johnson, Jason Leigh, Christina A.Vasilakis, Craig R. Barnes, and Thomas G. Moher {mroussos,ajohnson,jleigh,cvasilak,cbarnes,moher}@eecs.uic.edu Electronic Visualization Lab (EVL) & Interactive Computing Environments Lab (ICE) University of Illinois at Chicago 851 S. Morgan St., Room 1120 Chicago, IL 60607-7053 USA +1.312.996-3002 +1.312.413-7585 (FAX) nice@ice.eecs.uic.edu http://www.ice.eecs.uic.edu/~nice/

Object Type Directed Garbage Collection To Improve Locality

The Round Earth Project is a collaboration among researchers in computer science, education, and psychology. It investigates two alternative pedagogical strategies for teaching children that the Earth is spherical and the implications of that fact. One strategy, which we term the transformationalist approach, attempts to effect conceptual change by breaking down the childrens prior models. In contrast, the selectionist strategy attempts to effect learning in an alternative setting (in our case, a small-diameter asteroid), free of preexisting biases, and to relate that learning back to the target domain-the Earth. Virtual reality (VR) technologies support both pedagogical strategies. In the transformationalist approach, VR simulates the launching of a spacecraft from the Earths surface and subsequent exploration within a fixed-height orbit. In the selectionist approach, VR simulates a small-diameter asteroid.

Caching considerations for generational garbage collection

Most garbage collected systems have excessive need for RAM to achieve reasonable performance without too much paging. The reason for such poor locality is the way data are organized in the heap. Conventional organization approaches such as breadth-first ordering do not always bring objects in the same active working set together. When such co-active objects are distributed throughout the heap (on different memory pages), high paging costs will result from accessing objects during execution. To alleviate such poor ordering, researchers have tried many different approaches: depth-first ordering, dynamic reorganization, object creation ordering, and hierarchical decomposition. Each of these approaches has its associated costs, effectiveness, and limitations. This paper presents a new ordering approach to improve locality. By paying a little attention to object type and format, effective heuristics can be derived to group co-active objects together. To investigate this idea, a number of such object type directed grouping techniques are incorporated into a Scheme-48 system. Page fault reduction of up to an order of magnitude was observed.