Polle T. Zellweger

Scripted documents: a hypermedia path mechanism

The concept of a path, or ordered traversal of some links in a hypertext, has been a part of the hypertext notion from its early formation. Although paths can help to solve two major problems with hypertext systems, namely user disorientation and high cognitive overhead for users, their value has not been recognized. Paths can also provide the backbone for computations over a hypertext, an important issue for the future of hypertext. This paper constructs a framework for understanding path mechanisms for hypertext and explores the basic issues surrounding them. Given this framework, it reviews path mechanisms that have been provided by other hypertext systems. Finally, it describes the Scripted Documents system, which has been developed to test the potential of one powerful path mechanism.

A structural view of the Cedar programming environment

This paper presents an overview of the Cedar programming environment, focusing on its overall structure—that is, the major components of Cedar and the way they are organized. Cedar supports the development of programs written in a single programming language, also called Cedar. Its primary purpose is to increase the productivity of programmers whose activities include experimental programming and the development of prototype software systems for a high-performance personal computer. The paper emphasizes the extent to which the Cedar language, with run-time support, has influenced the organization, flexibility, usefulness, and stability of the Cedar environment. It highlights the novel system features of Cedar, including automatic storage management of dynamically allocated typed values, a run-time type system that provides run-time access to Cedar data type definitions and allows interpretive manipulation of typed values, and a powerful device-independent imaging modelthat supports the user interface facilities. Using these discussions to set the context, the paper addresses the language and system features and the methodologies used to facilitate the integration of Cedar applications. A comparison of Cedar with other programming environments further identifies areas where Cedar excels and areas where work remains to be done.

Multimedia conferencing in the Etherphone environment

The latest extension of the Etherphone project is described. It creates a powerful conferencing system that lets users control their participation in multiple conferences across multimedia networks. The emphasis is on the software mechanisms that support its new features: first, a Sparcstation facility called Phoenix that extends the Etherphone software architecture to permit more flexible conferencing and to control Sparcstation-based Ethernet audio transmission, and, second, the integration of the Phoenix capabilities with Macaw, the earlier video extensions. Also described is a multicast packet protocol for audio transmission, which reimplements and extends the earlier special-purpose protocols, adding per-channel volume control and full support for the extended conferencing modes.<<ETX>>

“I'll get that off the audio”: a case study of salvaging multimedia meeting records

We describe a case study of a complex, ongoing, collaborative work process, where the central activity is a series of meetings reviewing a wide range of subtle technical topics. The problem is the accurate repxting of the results of these meetings, which is the responsibility of a single person, who is not well-versed in all the topics. We provided tools to capture the meeting discussions and tools to “salvage” the cap tured multimedia recordings. Salvaging is a new kind of activity involving replaying, extracting, organizing, and writing. We observed a year of mature salvaging work in the case study. From this we describe the nature of salvage work (the constituent activities, the use of the workspace, the affordances of the audio medium, how practices develop and differentiate, how the content material affects practice). We also demonstrate how this work relates to the larger work processes (the task demands of the setting, the interplay of salvage with capture, the influence on the people being reported on and reported to). Salvaging tools are shown to be valuable for dealing with free-flowing discussions of complex subject matter and for producing high quality documentation.

Fluid links for informed and incremental link transitions

We have developed a novel user interface technique for hypertext, called fluid links, that has several advantages over current methods. Fluid links provide additional information at a link source to support readers in choosing among links and understanding the structure of a hypertext. Fluid links present this information in a convenient location that does not obscure the content or layout of the source material. The technique uses perceptually-based animation to provide a natural and lightweight feeling to readers. In their richer forms, fluid links can provide a novel hypertext navigation paradigm that blurs the boundaries of hypertext nodes and can allow readers to fluidly control the focus on the material to support their current reading goals.

Specifying temporal behavior in hypermedia documents

We have designed and implemented a system for creating, editing, and displaying hypermedia dOcuments. This system uses an improved document model with two major feat ures. First, it allows authors to specify temporal synchronization constraints among events of interest within media segments. Second, it allows asynchronous material, such as user interaction, links, or programs, to be combined with richly coordinated synchronous material in a single hypermedia document. The system incorporates a linear programming algorithm to solve the temporal constraints. This process automatically constructs a schedule for displaying a document and may involve stretching or shrinking media segments. Because synchronization constraints record the author’s intentions and because the system creates schedules automatically, both creating documents and maintaining them thr~ughout their life cycles should be easier.

City lights: contextual views in minimal space

City Lights are space-efficient fisheye techniques that provide contextual views along the borders of windows and subwindows that describe unseen objects in all directions. We present a family of techniques that use a range of graphical dimensions to depict varied information about unseen objects. City Lights can be used alone or in conjunction with scrollbars, 2D overview+detail, and interaction techniques such as zoomable user interfaces.

Fluid visualization of spreadsheet structures

Spreadsheets augment a visible tabular layout with invisible formulas. Direct manipulations of the tabular layout may or may not result in the desired changes to the formulas. The user is forced to explore the individual cells to find, verify, and modify the formulas, which causes heavy cognitive overhead. We present a set of techniques that make these formulas and their resulting dataflow structure easily accessible while maintaining the natural appearance of the spreadsheet. Transient local views visualize dataflow structures associated with individual cells, while static global views and animated global explanations visually present the entire dataflow structure at once. Semantic navigation enables the user to navigate through the dataflow structure interactively, and visual editing techniques make it possible to construct formulas using graphical editing techniques. Central to these techniques is the use of animation and lightweight interaction for rapid and non-intrusive visualization. Our prototype implementation suggests that these techniques can greatly improve the expressive power of current spreadsheets as well as other applications that have rich underlying structures.

Automatically generating consistent schedules for multimedia documents

A schedule for a multimedia document indicates when document events should occur. We describe a two-phase algorithm that automatically produces schedules for interactive multimedia documents, which can contain both predictable behavior (such as audio and video) and unpredictable behavior (such as user interaction and programs with unpredictable execution times). The first phase of the algorithm, called the compiletime scheduler, preprocesses high-level temporal specifications before the document is presented and creates as much of the schedule as possible. Our compiletime scheduler is conceptually similar to TEXs spatial layout algorithm in that it permits time to be stretched or shrunk between events inside media segments to arrive at an “optimal” presentation for a document. The second phase of the algorithm, called the runtime scheduler, resolves the presentation of media segments that depend upon unpredictable behavior.

The impact of fluid documents on reading and browsing: an observational study

Fluid Documents incorporate additional information into a page by adjusting typography using interactive animation. One application is to support hypertext browsing by providing glosses for link anchors. This paper describes an observational study of the impact of Fluid Documents on reading and browsing. The study involved six conditions that differ along several dimensions, including the degree of typographic adjustment and the distance glosses are placed from anchors. Six subjects read and answered questions about two hypertext corpora while being monitored by an eyetracker. The eyetracking data revealed no substantial differenccs in eye behavior between conditions. Gloss placement was significant: subjects required less time to use nearby glosses. Finally, the reaction to the conditions was highly varied, with several conditions receiving both a best and worst rating on the subjective questionnaires. These results suggest implications for the design of dynamic reading environments.