The particular focus of this chapter will be on a psychological theory of information scent (Pirolli, 1997, 2003; Pirolli & Card, 1999) that is embedded in a broader model (Pirolli & Fu, 2003) of information foraging on the Web. The notion of information scent also has been used in developing models of people seeking information in document-clustering browsers (Pirolli, 1997) and highly interactive information visualizations (Pirolli, Card, & Van Der Wege, 2003). Information scent refers to the cues used by information foragers to make judgments related to the selection of information sources to pursue and consume. These cues include items such as Web links or bibliographic citations that provide users with concise information about content that is not immediately available. The information scent cues play an important role in guiding users to the information they seek, and they also play a role in providing users with an overall sense of the contents of collections. The purpose of this paper is to present a theoretical account of information scent that supports the development of models of navigation choice.

Although large displays are becoming more cost effective, most user interfaces are optimized for a single monitor of modest size even though many traditional workspaces such as desks and workbenches are much larger and some studies have found benefits from large displays. This paper explores whether a single monitor is sufficient for information work using standard software. A log-based longitudinal field study finds that most of the time a single monitor allows skilled information analysts to have a reasonable pattern of window activity. However, a novel visualization of the data shows that windows typically fill the monitor and the pattern is occasionally interrupted by window thrashing, the rapid manipulation of windows caused by limited display resource. Given these findings, we identify some common tasks that justify the development and the expense of wideband visual interfaces that are optimized for larger displays.

Our work in the past five years on modeling user actions on the Web has shown that a great deal of information about user actions can be recovered from the informational cues processed by the user during navigation. We call these informational cues by the name of "Information Scent." We have shown in various papers that Information Scent can be used as a methodology for clustering a group of user profiles [Chi02], simulating a collection of users navigating thru the Web with an information need [Chi03], and provid-ing navigational cues to users with transient information goals [Olston03]. We argue in this position paper for a CHI2004 workshop that more research in user profiling should be done for user goals that are transient in nature.

Wideband displays fill our field of view, creating new opportunities to develop effective visual interfaces. Although multiple monitors are becoming an affordable way to create wideband displays, the resulting seams create gaps in words and divide diagonal lines into nonaligned segments. We present several novel user interface techniques for creating seam-aware applications, proving that vendors need not wait for affordable seamless displays to exploit the potential of wideband displays.

This paper describes the 3Book, a 3D interactive visualization of a codex book as a component for various digital library and sensemaking systems. The book is designed to hold large books and to support sensemaking operations by readers. The book includes methods in which the automatic semantic analysis of the book’s content is used to dynamically tailor access.

This paper describes the 3Book, a 3D interactive visualization of a codex book as a component for digital library and information-intensive applications. The 3Book is able to represent books of almost unlimited length, allows users to read large format books, and has features to enhance reading and sensemaking.

Subject indexes were an important step forward for books because they enabled the comparison and correlations of information without extensive reading, re-reading and memorization. In this short paper, we focus on the user interaction and usage scenario of a new system called ScentIndex that enhances the subject index of an eBook by conceptually reorganizing it to suit particular information needs. Users first enter information needs via keywords describing the concepts they are trying to retrieve and comprehend. ScentIndex then computes what index entries are conceptually related, and reorganizes and displays these index entries on a single page.

We present a new technique for efficiently computing Degree-of-Interest distributions to inform the visualization of graph-structured data. The technique is independent of the interest distribution used, and enables fluid interaction with very large data sets (over 100,000 nodes).

Although vendors have made multiple-monitor systems for many years, our interfaces have been stuck in a 30-year old windows paradigm focused on displays much smaller than the desktops we use when working with paper. Advances in flat panel displays and graphics cards now enable affordable personal computers with 6-8 monitors and may someday eliminate seams. This paper argues that vendors should be developing wideband visual interfaces that are designed for displays that fill the human visual field. We describe a longitudinal field study of window activity that found that windows almost always filled a typical single monitor display and that subjects occasionally struggled with window thrashing when they needed to work with two or more windows at the same time. Vendors need not wait for affordable seamless wideband displays before addressing these findings. We have implemented several novel user interface techniques for creating seam-aware applications that target wideband displays based on multiple monitors.

In this paper we describe a visualization architecture (AVID) that employs a dynamic model of user interest to support the design and creation of highly responsive, scalable visualizations of hierarchical data. We present evidence of the architecture's efficacy, showcasing dynamic visualizations with near-immediate (<100ms) update times, even on structures of over 100,000 nodes. We discuss how the key concepts used generalize to arbitrary graph structures. Additionally, we present the results of a user study comparing a prototypical visualization built using AVID to a more traditional file-browser interface, showcasing up to 20% improvement in information access times.

The two predominant paradigms for finding information on the Web are browsing and keyword searching. While they exhibit complementary advantages, neither paradigm alone is adequate for complex information goals that lend themselves partially to browsing and partially to searching. To integrate browsing and searching smoothly into a single interface, we introduce a novel approach called ScentTrails. Based on the concept of information scent developed in the context of information foraging theory, ScentTrails highlights hyperlinks to indicate paths to search results. This interface enables users to interpolate smoothly between searching and browsing to locate content matching complex information goals effectively. In a preliminary user study, ScentTrails enabled subjects to find information more quickly than by either searching or browsing alone.

No Abstract Available

According to usability experts, the top user issue for Web sites is difficult navigation. We have been developing auto-mated usability tools for several years, and here we describe a prototype service called InfoScent™ Bloodhound Simula-tor, a push-button navigation analysis system, which auto-matically analyzes the information cues on a Web site to produce a usability report. We further build upon previous algorithms to create a method called Information Scent Absorption Rate, which measures the navigability of a site by computing the probability of users reaching the desired destinations on the site. Lastly, we present a user study involving 244 subjects over 1385 user sessions that show how Bloodhound correlates with real users surfing for in-formation on four Web sites. The hope is that, by using a simulation of user surfing behavior, we can reduce the need for human labor during usability testing, thus dramatically lower testing costs, and ultimately improving user experience. The Bloodhound Project is unique in that we apply a concrete HCI theory directly to a real-world prob-lem. The lack of empirically validated HCI theoretical model has plagued the development of our field, and this is a step toward that direction.

This demonstration shows a method and implementation to interactively display large hierarchies (up to 10,000 nodes) within a web browser. This software computes a degree of interest (DOI) for each node in the hierarchy and displays an overview of the complete hierarchy while showing more detail for nodes with a higher DOI value.

This paper proposes Degree-of-Interest trees. These trees use degree-of-interest calculations and focus+context visualization methods, together with bounding constraints, to fit within pre-established bounds. The method is an instance of an emerging “attention-reactive” user interface whose components are de-signed to snap together in bounded spaces.

Web Usage Mining enables new understanding of user goals on the Web. This understanding has broad applications, and traditional mining techniques such as association rules have been used in business applications. We have developed an automated method to directly infer the major groupings of user traffic on a Web site [Heer01]. We do this by utilizing multiple data features in a clustering analysis. We have performed an extensive, systematic evaluation of the proposed approach, and have discovered that certain clustering schemes can achieve categorization accuracies as high as 99% [Heer02b]. In this paper, we describe the further development of this work into a prototype service called LumberJack, a push-button analysis system that is both more automated and accurate than past systems.

Visualization can be viewed as a process that transforms raw data (value) into views. There has been two major category of data process models that have been proposed to model the visualization transformation process. This paper seeks to compare the Data Flow Models and the Data State Models. Specifically, it proves that, in terms of expressiveness, anything that can represented using the Data Flow Model can also be represented using the Data State Model, and vice versa.

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No Abstract Available

In this paper, we introduce a concise and concrete definition of an accurate colon centerline and provide an efficient automatic means to extract the centerline and its associated branches (caused by a forceful touching of colon and small bowel or a deep fold in twisted colon lumen). We further discuss its applications on fly-through path planning and endoscopic simulation, as well as its potential to solve the challenging touching and colon collapse problems in virtual colonoscopy. Experimental results demonstrated its centeredness, robustness, and efficiency.

Predictive Web usage visualizations can help analysts uncover traffic patterns and usability problems.

Information visualization is the design and creation of interactive graphic depictions of information by combining principles in the disciplines of graphic design, cognitive science, and interactive computer graphics. This book describes a framework to make information visualization systems easier to develop through the creation of a reference model. It develops and discusses the general utility of this Data State Model, and validates it by applying it to various visualization techniques and showing several systems that illustrate issues such as how to model operators and interactions in visualization systems. The book also applies this reference model to make information visualization more accessible to potential users by creating a `Visualization Spreadsheet', where each cell can contain an entire set of data represented using interactive graphics.

This paper describes the visual analysis tool WebQuilt, a web usability logging and visualization system that helps web design teams record and analyze usability tests. The logging portion of WebQuilt unobtrusively gathers clickstream data as users complete specified tasks. This data is then aggregated and presented as an interactive graph, where nodes of the graph are images of the web pages visited, and arrows are the transitions between pages. To aid analysis of the gathered usability test data, the WebQuilt visualization provides filtering capabilities and semantic zooming, allowing the designer to understand the test results at the gestalt view of the entire graph, and then drill down to sub-paths and single pages. The visualization highlights important usability issues, such as pages where users spent a lot of time, pages where users get off track during the task, navigation patterns, and exit pages, all within the context of a specific task. WebQuilt is designed to conduct remote usability testing on a variety of Internet-enabled devices and provide a way to identify potential usability problems when the tester cannot be present to observe and record user actions.

Recent research has explored web user session clustering as a means of understanding user activity and interests on the World Wide Web. Though the proposed techniques have proven to be useful and effective, they require that one either specify the number of clusters in advance or browse a large hierarchy of clusters to find the optimal depth at which to describe user activity. In this paper, we examine the utility of a stability-based technique for automatically determining the optimal number of clusters in the context of web user session clustering. We present two case studies evaluating the technique’s effectiveness.

The Fluid Documents project has developed various research prototypes that show that powerful annotation techniques based on animated typographical changes can help readers utilize annotations more effectively. Our recently-developed Fluid Open Hypermedia prototype supports the authoring and browsing of fluid annotations on third-party Web pages. This prototype is an extension of the Arakne Environment, an open hypermedia application that can augment Web pages with externally stored hypermedia structures. This paper describes how various Web standards, including DOM, CSS, XLink, XPointer, and RDF, can be used and extended to support fluid annotations.

The Special Interest Group on Computer Human Interaction (SIGCHI) has had a successful history of 20 years of growth in its numbers and influence. To help guide the continued evolution of the academic discipline and professional community, we invite several senior members to offer their visions for what the field of CHI actually accomplished over the past several decades, and what do we still need to accomplish? What do we need to do differently/better/smarter? What haven't we tried because the technology, the money or the will wasn't there in the past, but perhaps is now? The CHI field is more than just technology. We understand that our work can have a profound effect on individuals, families, neighborhoods, corporations, and countries. We know that we can influence education, commerce, healthcare, and government. How can we contribute to bridging the digital divides in developed and developing countries? What agendas can we offer for the academic, research, industrial, and civic spheres for the next 20 years? How can we be more ambitious? How can we truly serve human needs?

On the Web, users typically forage for information by navigating from page to page along Web links. Their surfing patterns or actions are guided by their information needs. Researchers need tools to explore the complex interactions between user needs, user actions, and the structures and contents of the Web. In this paper, we describe two computational methods for understanding the relationship between user needs and user actions. First, for a particular pattern of surfing, we seek to infer the associated information need. Second, given an information need, and some pages as starting points, we attempt to predict the expected surfing patterns. The algorithms use a concept called “information scent”, which is the subjective sense of value and cost of accessing a page based on perceptual cues. We present an empirical evaluation of these two algorithms, and show their effectiveness.

Virtual endoscopy is a computerized, noninvasive procedure for detecting anomalies inside human organs. Several preliminary studies have demonstrated the benefits and effectiveness of this modality. Unfortunately, previous work cannot guarantee that an existing anomaly will be detected, especially for complex organs with multiple branches. In this paper, we introduce the concept of reliable navigation, which ensures the interior organ surface is fully examined by the physician performing the virtual endoscopy procedure. To achieve this, we propose computing a reliable fly-through path that ensures no blind area during the navigation. Theoretically, we discuss the criteria of evaluating a reliable path and prove that the problem of generating an optimal reliable path for virtual endoscopy is NP-complete. In practice, we develop an efficient method for the calculation of an effective reliable path. First, a small set of center observation points are automatically located inside the hollow organ. For each observation point, there exists at least one patch of interior surface visible to it, but that cannot be seen from any of the other observation points. These chosen points are then linked with a path that stays in the center of the organ. Finally, new points inside the organ are recursively selected and connected into the path until the entire organ surface is visible from the path. We present encouraging results from experiments on several data sets. For a medium size volumetric model with several hundred thousand inner voxels, an effective reliable path can be generated in several minutes.

Understanding user behaviors on Web sites enables site owners to make sites more usable, ultimately helping users to achieve their goals more quickly. Accordingly, researchers have devised methods for categorizing user sessions in hopes of revealing user interests. These techniques build user profiles by combining users' navigation paths with other data features, such as page viewing time, hyperlink structure, and page content. Previously, we have presented complex techniques of combining many of these data features to cluster user profiles. In this paper, we introduce a user study and a systematic evaluation of these different data features and their associated weighting schemes. We present the results of our study, including accuracy measures for a number of clustering approaches, and offer recommendations for Web analysts. While further investigation over more sites is needed to definitively settle on a robust scheme, we have characterized this analytic space.

WebQuilt is a web logging and visualization system that helps web design teams run usability tests (both local and remote) and analyze the collected data. Logging is done through a proxy, overcoming many of the problems with server-side and client-side logging. Captured usage traces can be aggregated and visualized in a zooming interface that shows the web pages people viewed. The visualization also shows the most common paths taken through the web site for a given task, as well as the optimal path for that task, as designated by the designer. This paper discusses the architecture of WebQuilt and also describes how it can be extended for new kinds of analyses and visualizations.

On the Web, users typically forage for information by navigating from page to page along Web links. Their surfing patterns or actions are guided by their information needs. Researchers need tools to explore the complex interactions between user needs, user actions, and the structures and contents of the Web. In this paper, we describe two computational methods for understanding the relationship between user needs and user actions. First, for a particular pattern of surfing, we seek to infer the associated information need. Second, given an information need, and some pages as starting points, we attempt to predict the expected surfing patterns. The algorithms use a concept called “information scent”, which is the subjective sense of value and cost of accessing a page based on perceptual cues. We present an empirical evaluation of these two algorithms, and show their effectiveness.

Eye trackers output a stream of points at which the eye was looking. To give these points meaning, researchers analyzing eye tracking data need to map the points onto the meaningful objects at which the eye was looking. Performing this mapping has proven to be a tedious, time-consuming task. We present a software system that automates this task for Web usability studies that incorporate eye tracking.

We introduce a technique for creating novel, textually-enhanced thumbnails of Web pages. These thumbnails combine the advantages of image thumbnails and text summaries to provide consistent performance on a variety of tasks. We conducted a study in which participants used three different types of summaries (enhanced thumbnails, plain thumbnails, and text summaries) to search Web pages to find several different types of information. Participants took an average of 67, 86, and 95 seconds to find the answer with enhanced thumbnails, plain thumbnails, and text summaries, respectively. We found a strong effect of question category. For some questions, text outperformed plain thumbnails, while for other questions, plain thumbnails outperformed text. Enhanced thumbnails (which combine the features of text summaries and plain thumbnails) were more consistent than either text summaries or plain thumbnails, having for all categories the best performance or performance that was statistically indistinguishable from the best.

In this paper, we present three taxonomic classification schemes based on Web users' responses to what Web activities significantly impacted their decisions and actions. The taxonomic classifications focus on three variables: the Purpose of people's search on the Web, the Method people use to find information, and the Content of the information for which they are searching. These taxonomies are useful for understanding people's activity on the Web and for developing ecologically-valid tasks to be used when studying web behavior.

In this paper, we describe an electronic guidebook prototype and report on a study of its use in a historic house. Supported by mechanisms in the guidebook, visitors constructed experiences that had a high degree of interaction with three entities: the guidebook, their companions, and the house and its contents. For example, we found that most visitors played audio descriptions through speakers (rather than using headphones or reading textual descriptions) to facilitate communication with their companions.

We describe tap tips, a technique for providing touch-screen target location hints. Tap tips are lightweight in that they are non-modal, appear only when needed, require a minimal number of user gestures, and do not add to the standard touchscreen gesture vocabulary. We discuss our implementation of tap tips in an electronic guidebook system and some usability test results.

Eye tracking studies of the Hyperbolic Tree browser suggest that visual search in focus+context displays is highly affected by information scent (i.e., local cues, such as text summaries, used to assess and navigate towards distal information sources). When users detected a strong information scent, they were able to reach their goal faster with the Hyperbolic Tree browser than with a conventional browser. When users detected a weak scent or no scent, users exhibited less efficient search of areas with a high density of visual items. In order to interpret these results we present an integration of the CODE Theory of Visual Attention (CTVA) with information foraging theory. Development of the CTVA-foraging theory could lead to deeper analysis of interaction with visual displays of content, such as the World Wide Web or information visualizations.

The purpose of this paper is to introduce a replicable WWW protocol analysis methodology illustrated by application to data collected in the laboratory. The methodology uses instrumentation to obtain detailed recordings of user actions with a browser, caches Web pages encountered, and videotapes talk-aloud protocols. We apply the current form of the method to the analysis of eight Web protocols, visualizing the structure of the interaction and showing the strong effect of information scent in determining the path followed.

The complexity of software has continuously risen since the invention of the computer, and while Moore's law predicts the growth in processor speed, it fails to take into account our ability in managing complex software processes. Our utilization of the increase in processor speed is very much dependent on our ability to manage this complexity.

Previously, we presented a system called AlignmentViewer that uses information visualization techniques to visualize similarities between a single DNA sequence and a large database of other sequences. In this paper, we extend, summarize, and describe the system using several interesting case studies. We present our comb glyph technique for visualizing alignments between sequences. In this paper, we also extend the original system by incorporating computational steering, and the visualization of differences between data sets. The case studies and the new extended system present our novel approach of extracting significant relationships in the biological data set.

Data visualization environments help users understand and analyze their data by permitting interactive browsing of graphical representations of the data. To further facilitate understanding and analysis, many visualization environments have special features known as portals, which are sub-windows of a data canvas. Portals provide a way to display multiple graphical representations simultaneously, in a nested fashion. This makes portals an extremely powerful and flexible paradigm for data visualization. Unfortunately, with this flexibility comes complexity. There are over a hundred possible ways each portal can be configured to exhibit different behaviors. Many of these behaviors are confusing and certain behaviors can be inappropriate for a particular setting. It is desirable to eliminate confusing and inappropriate behaviors. In this paper, we construct a taxonomy of portal behaviors and give recommendations to help designers of visualization systems decide which behaviors are intuitive and appropriate for a particular setting. We apply these recommendations to an example setting that is fully visually programmable and analyze the resulting reduced set of behaviors. Finally, we consider a real visualization environment and demonstrate some problems associated with behaviors that do not follow our recommendations.

In previous work, researchers have attempted to construct taxonomies of information visualization techniques by examining the data domains that are compatible with these techniques. This is useful because implementers can quickly identify various techniques that can be applied to their domain of interest. However, these taxonomies do not help the implementers understand how to apply and implement these techniques. In this paper, we will extend and then propose a new way to taxonomize information visualization techniques by using the Data State Model. In fact, as the taxonomic analysis in this paper will show, many of the techniques share similar operating steps that can easily be reused. The paper shows that the Data State Model not only helps researchers understand the space of design, but also helps implementers understand how information visualization techniques can be applied more broadly.

Item selection is a key problem in electronic guidebook design. Many systems do not apply so-called "context-awareness" technologies to infer user interest, placing the entire burden of selection on the user. Conversely, to make selection easier, many systems automatically eliminate information that they infer is not of interest to the user. However, such systems often eliminate too much information, preventing the user from finding what they want. To realize the full potential of electronic guidebooks, designers must strike the right balance between automatic context-based inference and manual selection. In this paper, we introduce a task-oriented model of item selection for electronic guidebooks to help designers explore this continuum. We argue that item selection contains three sub-tasks and that these sub-tasks should be considered explicitly in system design. We apply our model to existing systems, demonstrating pitfalls of combining sub-tasks, and discuss how our model has improved the design of our own guidebook prototype.

No Abstract Available

Considering the amount of interest in studying Web-browsing behavior, there is a relative lack of tools for data collection in this area. Those tools that do exist have significant limitations on the data they are able to collect or on their suitability for efficient analysis. We present WebLogger, a tool which instruments Microsoft's Internet Explorer Web browser. We have found that WebLogger alleviates some of the problems associated with other approaches to browser-based data collection methods.

A multiple view system uses two or more distinct views to support the investigation of a single conceptual entity. Many such systems exist, ranging from computer-aided design (CAD) systems for chip design that display both the logical structure and the actual geometry of the integrated circuit to overview-plus-detail systems that show both an overview for context and a zoomed-in-view for detail. Designers of these systems must make a variety of design decisions, ranging from determining layout to constructing sophisticated coordination mechanisms. Surprisingly, little work has been done to characterize these systems or to express guidelines for their design. Based on a workshop discussion of multiple views, and based on our own design and implementation experience with these systems, we present eight guidelines for the design of multiple view systems.

Focus + context information visualizations have sought to amplify human cognition by increasing the amount of information immediately available to the user. We study how the focus + context distortion of the Hyperbolic Tree browser affects information foraging behavior in a task similar to the CHI '97 Browse Off. In comparison to a more conventional browser, Hyperbolic users searched more nodes, searched at a faster rate, and showed more learning. However, the performance of the Hyperbolic was found to be highly affected by "information scent", proximal cues to the value of distal information. Strong information scent made hyperbolic search faster than with a conventional browser. Conversely, weak scent put the hyperbolic tree at a disadvantage. There appears to be two countervailing processes affecting visual attention in these displays: strong information scent expands the spotlight of attention whereas crowding of targets in the compressed region of the Hyperbolic narrows it. The results suggest design improvements.

Visual computational steering environments extend traditional visualization environments by enabling the user to interactively steer the computations applied to the data. In this paper, we develop a new type of computational steering. "Resource steering" extends current visual steering techniques by providing machine resource estimation and control to the user. With resource steering, the user controls the execution of the computation on a parallel or distributed computer based on experimentally or theoretically derived estimates of the parallel performance of the computation. We demonstrate this extended steering model by applying it to an information visualization system that analyzes genetic sequence similarity reports. We show how our extended steering model enhances the user's ability to control visualization computations.

Digital books can significantly enhance the reading experience, providing many functions not available in printed books. In this paper we study a particular augmentation of digital books that provides readers with customized recommendations. We systematically explore the application of spreading activation over text and citation data to generate useful recommendations. Our findings reveal that for the tasks performed in our corpus, spreading activation over text is more useful than citation data. Further, fusing text and citation data via spreading activation results in the most useful recommendations. The fused spreading activation techniques outperform traditional text-based retrieval methods. Finally, we introduce a preliminary user interface for the display of recommendations from these algorithms.

Designers and researchers of users' interactions with the World Wide Web need tools that permit the rapid exploration of hypotheses about complex interactions of user goals, user behaviors, and Web site designs. We present an architecture and system for the analysis and prediction of user behavior and Web site usability. The system integrates research on human information foraging theory, a reference model of information visualization and Web data-mining techniques. The system also incorporates new methods of Web site visualization (Dome Tree, Usage Based Layouts), a new predictive modeling technique for Web site use (Web User Flow by Information Scent, WUFIS), and new Web usability metrics.

In the process of knowledge discovery, workers examine available information in order to make sense of it. By sensemaking, we mean interacting with and operating on the information with a variety of information processing mechanisms [3, 18]. Previously, we introduced a concept that uses the spreadsheet metaphor with cells containing visualizations of complex data. In this paper, we extend and apply a cognitive model called "visual sensemaking" to the Visualization Spreadsheet. We use the task of making sense of a large Web site as a concrete example throughout the paper for demonstration. Using a variety of visualization techniques, such as the Disk Tree and Cone Tree, we show that the interactions of the Visualization Spreadsheet help users draw conclusions from the overall relationships of the entire information set.

In this paper, we present methods in information visualization that apply to the discovery of patterns in World-Wide Web sites. We hope to use techniques of information visualization to help in the organization and categorization of Web sites. We present a detailed case study of using the spreadsheet to analyze the content, usage, and structure of a large Web site. We demonstrate how the visualization spreadsheet principles apply in this specific data domain.

Modeling and predicting user surfing paths involves tradeoffs between model complexity and predictive accuracy. In this paper we explore predictive modeling techniques that appempt ot reduce model complexity while retaining predictive accuracy. We show that compared to various Markov models, longest repeating subsequence models are able to significantly reduce model size while retaining the ability to make accurate predictions. Sharp increases in the overall predictive capabilities of these models are achievable by models increases to the size of the number of predictions made.

No Abstract Available

Information Foraging Theory is an approach to understanding how strategies and technologies for information seeking, gathering and consumption are adapted to the flux of information in the environment. The theory assumes that people, when possible, will modify their strategies or the structure of the environment to maximize their rate of gaining valuable information. Field studies inform the theory by illustrating that people do freely structure their environments and their strategies to yield high gains in information foraging. The theory is developed by (a) adaptation (rational) analysis of information foraging problems and (b) a detailed process model (ACT-IF). The adaptation analysis develops (a) information patch models, which deal with time allocation and information filtering and enrichment activities in environments in which information is encountered in clusters (e.g. bibliographic collections), (b) information scent models which address the identification of information value from proximal cues, and (c) information diet models which address decisions about the selection and pursuit of information items. ACT-IF is developed to instantiate these rational models and to fit the moment-by-moment behavior of people interacting with complex information technology. ACT-IF is a production system in which the information scent of bibliographic stimuli is calculated by spreading activation mechanisms. Time allocation and item selection heuristics make use of information sent to select production rules in ways that maximize information foraging activities.

(First paragraph) We engage our physical and social environments through highly evolved technologies, in interactions that often require sophisticated knowledge and virtuoso performance. Finding the order underlying the complexity of these interactions may be one of the most daunting challenges facing science. Over the past few decades, the study of human-computer interaction (HCI) has become an increasingly important arena for pursuing this challenge. HCI is a discipline concerned with the study and design of interactive computing systems used by people towards satisfying their goals. HCI has become an arena in which new computer applications can benefit from new cognitive engineering models that synthesize results from sound cognitive science. It has also become a useful testbed for cognitive architectures, which are integrated theories of psychological mechanisms that aim to predict complex learning, cognition, and performance. This chapter provides an overview of cognitive engineering models and cognitive architectures in the context of HCI.

Multiple studies have shown that clutter or sparsity in visual representations can have negative effects ranging from decreased user performance to diminished visual appeal. We have developed a system that assists users in the construction and navigation of visualizations with appropriate visual information density. This system, VIDA (Visual Information Density Adjuster), applies a cartographic principle to minimize clutter and sparsity in visual displays of information.

Surfing the World Wide Web (WWW) involves traversing hyperlink connections among documents. The ability to predict surfing patterns could solve many problems facing producers and consumers of WWW content. We analyzed WWW server logs for a WWW site, collected over ten days, to compare different path reconstruction methods and to investigate how past surfing behavior predicts future surfing choices. Since log files do not explicitly contain user paths, various methods have evolved to reconstruct user paths. Session times, number of clicks per visit, and Levenshtein Distance analyses were performed to show the impact of various reconstruction methods. Different methods for measuring surfing patterns were also compared. Markov model approximations were used to model the probability of users choosing links conditional on past surfing paths. Information-theoretic (entropy) measurements suggest that information is gained by using longer paths to estimate the conditional probability of link choice given surf path. The improvements diminish, however, as one increases the length of path beyond one. Information-theoretic (Total Divergence to the Average entropy) measurements suggest that the conditional probabilities of link choice given surf path are more stable over time for shorter paths than longer paths. Direct examination of the accuracy of the conditional probability models in predicting test data also suggests that shorter paths yield more stable models and can be estimated reliably with less data than longer paths.

Information has become interactive. Information visualization is the design and creation of interactive graphic depictions of information by combining principles in the disciplines of graphic design, cognitive science and interactive computer graphics. As the volume and complexity of the data increases, users require more powerful visualization tools that allow them to more effectively explore large abstract datasets. This thesis seeks to make information visualization more accessible to potential users by creating a "Visualization Spreadsheet", where each cell can contain an entire set of data represented using interactive graphics. Just as a numeric spreadsheet enables exploration of numbers, a visualization spreadsheet enables exploration of visual forms of information. Unlike numerical spreadsheets, which store only simple data elements and formulas in each cell, a cell in the Visualization Spreadsheet can hold an entire abstract data set, selection criteria, viewing specifications, and other information needed for a full-fledged information visualization. Similarly, intra-cell and inter-cell operations are far more complex, stretching beyond simple arithmetic and string operations to encompass a range of domain-specific operators. The complexity of operations and interactions requires a visualization framework that is easily understandable to both end-users and visualization designers. This thesis develops and discusses the general utility of a novel visualization framework, and validates the framework by applying it to various visualization techniques and showing several systems that illustrate some of these research issues. We show that the spreadsheet approach facilitates certain visual user tasks that are more difficult using other approaches. The underlying approach in our work allows domain experts to define new data types and data operations and enable visualization experts to incorporate new visualizations, viewing parameters, and view operations.

To date there have been a number of efforts that attempt to characterize various aspects of the World Wide Web. This paper presents a summary of these efforts, highlighting regularities and insights that have been discovered across the variety of access points available for instrumentation. Characterizations that are derived from client, proxy, and server instrumentation are reviewed as well as effort to characterize the entire structure of the WWW. Given the dynamic nature of the Web, it may be surprising for some readers to find that many properties of the Web follow regular and predictable patterns that have not changed in form over the Web's lifetime. Understanding theses aspects as well as those that vary is critical to designing a better Web, and as a direct consequence, creating amore enjoyable user experience.

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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 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.

We introduce a novel zoom method, goal-directed zoom. In a goal directed zoom system, users specify which representation of an object they wish to see. The system automatically zooms to the elevation at which that representation appears at appropriate detail. We have extended a database visualization environment to support end-user construction of visualization that have goal directed zoom. We present a sample visualization we have constructed using this environment.

We introduce a system that helps users construct interactive visualizations with constant information density. This work is an extension of the DataSplash database visualization environment. DataSplash is a direct manipulation system in which users can construct and navigate visualizations. Objects' appearances change as users zoom closer to or further away from the visualization. Users specify graphically the point at which these changes occur. Our experience with DataSplash indicates that users find it difficult to construct visualizations that display an appropriate amount of detail. In this paper, we introduce an extension to DataSplash based on the Principle of Constant Information Density. Thins extension gives users feedback about the density of visualizations as they create them. We also introduce an extension that suggests improvements to existing visualizations. We have performed an informal study of user navigation in applications with and without constant information density. We suggest that designers take density into account when designing applications to avoid biasing user navigation in unexpected ways.

The cartographic Principle of Constant Information Density suggests that the amount of information in an interactive visualization should remain constant as the user pans and zooms. In previous work, we presented a system, VIDA (Visual Information Density Adjuster), which helps users manually construct applications in which overall display density remains constant. In the context of semantic zoom systems, this approach ensures uniformity in the z dimension, but does not extend naturally to ensuring uniformity in the x and y dimensions. In this paper, we present a new approach that automatically creates displays that are uniform in the x, y, and z dimensions. In the new system, users express constraints about visual representations that should appear in the display. The system applies these constraints to subdivisions of the display such that each subdivision meets a target density value. We have implemented our technique in the DataSplash/VIDA database visualization environment. We describe our algorithm, implementation, and the advantages and disadvantages of our approach.

To date there have been a number of efforts that attempt to characterize various aspects of the World Wide Web. This paper represents a summary of these efforts, highlighting regularities and invariants that have been discovered.

We develop an approach to the measurement of knowledge content, knowledge access and knowledge learning. This approach has two elements: First we describe a theoretical view of cognition, called the Newell-Dennett framework, which we see as being particularly favorable to the development of a measurement approach. Then, we describe a class of measurement models, based on Rasch modeling, which we see as being particularly favorable to the development of cognitive theories. Knowledge content and access are viewed as determining the observable actions selected by an agent in order to achieve desired goals in observable situations. To the degree that models within the theory fit the data at hand, one considers measures of observed behavior to be manifestations of intelligent agents having specific classes of knowledge content and varying degrees of access to that knowledge. Although agents, environment, and knowledge are constitutively defined (in terms of one another), successful application of our theory affords separation of parameters associated with the person from those associated with the environment. We present and discuss two examples of measurement models developed within our approach that address the evolution of cognitive skill, strategy choice and application, and developmental changes in mixtures of strategy use.

Information Foraging (IF) Theory addresses user strategies and technology for seeking, gathering, and using on-line information. We present IF-based models and evaluations of two interfaces: the Scatter/Gather browser for large document collections, and the Butterfly interface for surfing the citation link structure of scientific literatures. A computational cognitive model, ACT-IF, models observed users by assuming that they have heuristics that optimize their information foraging behavior in accordance with IF theory.

Designers and researchers of human-computer interaction need tools that permit the rapid exploration and management of hypotheses about complex interactions of designs, task conditions, and user strategies. Dynamic programming is introduced as a such a tool for the analysis of information foraging technologies. The technique is illustrated in the context of the Scatter/Gather text clustering browser. Hypothetical improvements in browser speed and text clustering are examined in the context of variations in task deadlines and the quality of the document repository. A complex and non-intuitive set of tradeoffs emerge from even this simple space of factors, illustrating the general utility of the approach.

(First paragraph) The purpose of this workshop was to develop an appreciation and understanding of the METOC function for Naval Operations. Then, using a scenario-based group discussion method, develop recommendations to facilitate the METOC function.

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.

One of the most common modes of accessing information in the World Wide Web is surfing from one document to another along hyperlinks. Several large empirical studies have revealed common patterns of surfing behavior. A model that assumes that users make a sequence of decisions to proceed to another page, continuing as long as the value of the current page exceeds some threshold, yields the probability distribution for the number of pages that a user visits within a given Web site. This model was verified by comparing its predictions with detailed measurements of surfing patterns. The model also explains the observed Zipf-like distributions in page hits observed at Web sites.

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Information visualization encounters a wide variety of different date domains. The visualization community has developed representation methods and interactive techniques. As a community, we have realized that the requirements in each domain are often dramatically different. In order to easily apply existing methods, researchers have developed a semiology of graphic representation. We have extended this research into a framework that includes operators and interactions in visualization systems, such as a visualization spreadsheet. We discuss properties of this framework and use it to characterize operations spanning a variety of different visualization techniques. The framework developed in this paper enables a new way of exploring and evaluating the design space of visualization operators, and helps end-users in their analysis tasks.

Spreadsheets have proven highly successful for interacting with numerical data, such as applying algebraic operations, refining data propagation relationships, manipulating rows or columns, and exploring "what-if" scenarios. Spreadsheet techniques have recently been extended from numeric domains to other domains. Here we present a spreadsheet approach to displaying and exploring information visualizations, with large, abstract, multidimensional data sets that are visually represented in multiple ways. We illustrate how spreadsheet techniques provide a structured, intuitive, and powerful interface for investigating information visualizations. An earlier version of this article appeared in the proceedings of the 1997 Information Visualization Symposium. Here we refocus the discussion to illustrate principles that make the spreadsheet approach powerful. These principles show how we can perform many user tasks easily in the visualization spreadsheet that prove much more difficult using other approaches.

Several visualizations have emerged which attempt to visualize all or part of the World Wide Web. Those visualizations, however, fail to present the dynamically changing ecology of users and documents on the Web. We present new techniques for Web Ecology and Evolution Visualization (WEEV). Disk Trees represent a discrete time slice of the Web ecology. A collection of Disk Tress forms a Time Tube, representing the evolution of the Web over longer periods of time. These visualizations are intended to aid authors and webmasters with the production and organization of content, assist Web surfers making sense of information, and help researchers understand the Web.

The information presented in a document often consists of primary content as well as supporting material such as explanatory notes, detailed derivations, illustrations, and the like. We introduce a class of user interface techniques for fluid documents that supports the reader's shift to supporting material while maintaining the context of the primary material. Our approach initially minimizes the intrusion of supporting material by presenting it as a small visual cue near the annotated primary material. When the user expresses interest in the annotation, it expands smoothly to a readable size. At the same time, the primary material makes space for the expanded annotation. The expanded supporting material must be given space to occupy, and it must be made salient with respect to the surrounding primary material. These two aspects, space and salience, are subject to a negotiation between the primary and supporting material. This paper presents the components of our fluid document techniques and describes the negotiation architecture for ensuring that the presentations of both primary and supporting material are honored.

In information visualization, as the volume and complexity of the date increases, researchers require more powerful visualization tools that enable them to more effectively explore multidimensional datasets. In this paper, we discuss the general utility of a novel visualization spreadsheet framework. Just as a numerical spreadsheet enables exploration of numbers, a visualization spreadsheet enables exploration of visual forms of information. We show that the spreadsheet approach facilitates certain information visualization tasks that are more difficult using other approaches. Unlike traditional spreadsheets, which store only simple data elements and formulas in each cell, a visualization spreadsheet cell can hold an entire complex data set, selection criteria, viewing specifications, and other information needed for a full-fledged information visualization. Similarly, inter-cell operations are far more complex, stretching beyond simple arithmetic and string operations to encompass a range of domain-specific operators. We have built two prototype systems that illustrate some of these research issues. The underlying approach in our work allows domain experts to define new data types and data operations, and enables visualization experts to incorporate new visualizations, viewing parameters, and view operations.

The lineage of a datum records its processing history. Because such information can be used to trace the source of anomalies and errors in processed data sets, it is valuable to users for a variety of applications including investigation of anomalies and debugging. Traditional data lineage approaches rely on metadata. However, metadata does not scale well to fine-grained lineage, especially in large data sets. For example, it is not feasible to store all of the information necessary to trace from a specific floating point value in a processed data set to a particular satellite image pixel in a source data set. In this paper, we propose a novel method to support fine-grained data lineage. Rather than relying on metadata, our approach lazily computes lineage using a limited amount of information about the processing operators and the base data. We introduce the notions of weak inversion and verification. While our system does not perfectly invert the data, it uses weak inversion and verification to provide a number of guarantees about the lineage it generates. We propose a design for the implementation of weak inversion and verification in an object-relational database management system.

The WWW is currently the hottest test-bed for future interactive digital systems. While much is understood technically about how the WWW functions, substantially less is known about how this technology is used collectively and on an individual basis. This disparity of knowledge exists largely as a direct consequence of the decentralized nature of Web. Since each user of the Web is not uniquely identifiable across the system and the system employs various levels of caching, measurement of actual usage is problematic. This paper establishes terminology to frame the problem of reliably determining usage of WWW resources while reviewing current practice and their shortcomings. A review of the various metrics and analyses that can be performed to determine usage is then presented. This is followed by a discussion of the strengths and weaknesses of the hit-metering proposal [Mogul and Leach 1997] currently in consideration by the HTTP working group. Lastly, new proposals, based upon server-side sampling are introduced and assessed against the other proposal. It is argued that server-side sampling provides more reliable and useful usage data while requiring no change to the current HTTP protocol and enhancing user privacy.

In information visualization, as the volume and complexity of the data increases, researchers require more powerful visualization tools that allow them to more effectively explore multi-dimensional datasets. In this paper, we show a novel new visualization framework built upon the spreadsheet metaphor, where each cell can contain an entire dataset. Just as a numerical spreadsheet enables exploration of numbers, a visualization spreadsheet enables exploration of visualizations of data. Our prototype spreadsheet enabled users to compare visualizations in cells using the tabular layout. Users can use the spreadsheet to display, manipulate, and explore multiple visual representation techniques for their data. By applying different operations to the cells, we showed how visualization spreadsheets afford the construction of 'what-if' scenarios. The possible set of operations that users can apply consists of animation, filtering, and algebraic operators.

One of the fastest growing sources of information today is the World Wide Web (WWW), having grown from only fifty sources of information in January of 1993 to over a half million four years later. The exponential growth of information within the Web has created an overabundance of information and a poverty of human attention, with users citing the inability to navigate and find relevant information on the Web as one of the biggest problems facing the Web today. The primary goal of the research presented here is to put forth new techniques and models that can be used to help efficiently manage people's attentional processes when dealing with large, unstructured, heterogeneous information environments. The primary model is based upon the desirability of items on the Web. This research searches for lawful patterns of structure, content, and use. Methods are developed to exploit these patterns to organize and optimize users' information foraging and sensemaking activities. The enhancements rely on predicting, categorization and allocation of attention. Several methods are explored for inducing categorical structures for the WWW. Some of these enhancements involve clustering in a high-dimensional space of content, use, and structural features. Others derive from cocitation analysis methods used in the study of scientific communities. A user would also be aided by retrieval mechanisms that predicted and returned the most likely needed WWW pages, given that the user is attending to some given page(s). The approach of this research uses a spreading activation mechanism to predict the needed, relevant information, computed using past usage patterns, degree of shared content, and WWW hyperlink structure.

We present Information Foraging Theory as an approach to understanding how strategies and technologies for information seeking, gathering, and consumption are adapted to the flux of information in the cultural environment. The theory is developed within an evolutionary-ecological framework that includes analysis of adaptation, knowledge, and cognition. The theory is applied to field studies, controlled experiments, and technology design. We present the Information Diet Model and Information Patch Residence Time Model as optimization models of information foraging under some strong constraints. These are used to develop a specific production system model called ACT-IF that predicts the fine-grained information seeking and gathering behavior of participants using a sophisticated document browsing system. We also present the Overlapped Patch Foraging with Queueing Model to address situations in which information search and information handling may occur in parallel, the Extreme Variance Rule which deals with information foraging under deadlines and uncertainty, a general class of Dynamic Information Foraging Models, and the Hogg-Huberman Model of the phase space of cost functions for heuristic information search.

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We report on our examination of pages from the World Wide Web. We have analyzed data collected by the Inktomi Web crawler (this data currently comprises over 2.6 million HTML documents). We have examined many characteristics of these documents, including: document size; number and types of tags, attributes, file extensions, protocols, and ports; the number of in-links; and the ratio of document size to the number of tags and attributes. For a more limited set of documents, we have examined the following: the number and types of syntax errors and readability scores. These data have been aggregated to create a number of ranked lists, e.g., the ten most-used tags, the ten most common HTML errors.

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Vast amounts of attention and resources have recently been devoted toward the World Wide Web (WWW) [1], but relatively little research has been conducted examining Web usage and societal implications. With the goals of understanding the Web user population and promoting the Web as a viable surveying medium, the WWW User Surveys were initially conducted by Georgia Institute of Technology's Graphics, Visualization, and Usability center during January of 1994. Subsequent surveys have been administered approximately every six months thereafter. Each survey is conducted for one month using the limited interactivity of the Web, where users point and click on responses within their Web browsers and submit results to a centralized server for processing. The first survey [6] was administered during January 1994 and received over 1,500 responses, which was a considerable amount at that time. This response rate, along with tremendous positive feedback from the Web community, justified continuing the surveys. The second survey (October 1994) [7] employed an extended and refined question base, which included a set of questions developed by the University of Michigan's Hermes Team regarding consumer attitudes toward electronic commerce. The response rate continued to grow significantly, recording over 4,500 unique users. This tremendous growth has continued through the third and fourth surveys (April and October 1995) [4,5], with 13,000 and 23,300 users responding, respectively. Based upon current estimates, the last two surveys were completed by nearly one out of every thousand web users [2,3]. We expect this trend to continue for the fifth survey, the results of which will be available in mid-June 1996.

In its current implementation, the World-Wide Web lacks much of the explicit structure and strong typing found in many closed hypertext systems. While this property has directly fueled the explosive acceptance of the Web, it further complicates the already difficult problem of identifying usable structures and aggregates in large hypertext collections. These reduced structures, or localities, form the basis to simplifying visualizations of and navigation through complex hypertext systems. Much of the previous research into identifying aggregates utilize graph theoretic algorithms based upon structural topology, i.e., the linkages between items. Other research has focused on content analysis to form document collections. This paper presents our exploration into techniques that harness both the topology and textual similarity between items as well as integrate new analyses based upon actual usage of the Xerox's WWW space. Linear equations and spreading activation models are employed to arrange Web pages based upon functional categories, node types, and relevancy.

In its current implementation, the World Wide Web lacks much of the explicit structure and strong typing found in many closed hypertext systems. While this property probably relates to the explosive acceptance of the Web, it further complicates the already difficult problem of identifying usable structures and aggregates in large hypertext collections. These reduced structures, or localities, form the basis for simplifying visualizations of and navigation through complex hypertext systems. Much of the previous research into identifying aggregates utilize graph theoretic algorithms based upon structural typology, i.e. the linkage between items. Other research has focused on content analysis to form document collections. This paper presents our exploration into techniques that utilize both the topology and textual similarity between items as well as usage data collected by servers and page meta-information like title and size. Linear equations and spreading activation models are employed to arrange Web pages based upon functional categories, node types and relevancy.

Five years is not very long on most historical scales, but for the World Wide Web (WWW) it constitutes a lifetime. A question almost as old as the web itself is, "Who is using it, and for what?" One way to answer this question is to use paper surveys, telephone survey, or diaries which are some of the same methods used to measure the audiences of other one-way media such as television and radio. However, something interesting happened in early 1994: the implementation of HTML Forms turned the web into a two-way medium which made it possible to contact the audience directly. To test the viability of the web as a survey medium and collect preliminary data on the web population, the first GVU WWW User Survey was conducted in January 1994. Subsequent surveys have been conducted approximately every six months. The collection of responses from over 55,000 Web users over five surveys has given us a unique perspective on the advances in surveying technology and methodology and changes in the web population itself. In the following sections we discuss what we have learned in each of these areas.

Information visualization faces challenges presented by the need to represent abstract data and the relationships within the data. Previously, we presented a system for visualizing similarities between a single DNA sequence and a large database of other DNA sequences [6]. Similarity algorithms generate similarity information in textual reports that can be hundreds or thousands of pages long. Our original system visualized the most important variables from these reports. However, the biologists we work with found this system so useful they requested visual representations of other variables. We present an enhanced system for interactive exploration of this multivariate data. We identify a larger set of useful variables in the information space. The new system involves more variables, so it focuses on exploring subsets of the data. We present an interactive system allowing mapping of different variables to different axes, incorporating animation using a time-axis, and providing tools for viewing subsets of the data. Detail-on-demand is preserved by hyperlinks to the analysis reports. We present three case studies illustrating the use of these techniques. The combined technique of applying a time axis with a 3D scatter plot and query filters to visualization of biological sequenced similarity data is both powerful and novel.

The World-Wide Web has achieved global connectivity stimulating the transition of computers from knowledge processors to knowledge sources. But the Web and its client software are seriously deficient for supporting users' interactive use of this information. This paper presents two related designs with which to evolve the Web and its clients. The first is the WebBook, a 3D interactive book of HTML pages. The WebBook allows rapid interaction with objects at a higher level of aggregation than pages. The second is the Web Forager, an application that embeds the WebBook and other objects in a hierarchical 3D workspace. Both designs are intended as exercises to play off against analytical studies of information workspaces.

This paper reports on user experience with Tioga, a DBMS-centric visualization tool developed at Berkeley. Based on this experience, we have designed Tioga-2 as a direct manipulation system that is more powerful and much easier to program. A detailed design of the revised system is presented, together with an extensive example of its application.

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In "The Digital Library Project: The World of Knowbots" in Part 1, Robert Kahn and Vinton Cerf ask, "If a thousand books are combined on a single CD-ROM and the acquirer of the CD-ROM only intends to read one of them, what sort of royalty arrangement is appropriate to compensate the copyright owners? How would compensation be extended for cases in which electronic copies are provided to users?" Their questions show how, in 1988, issues about copyright protection and payment for using information arose in the context of early CD-ROM distribution. By 1994 copyright issues had not only not been settled, they were coming to a boil. Laura Fillmore's effort to build a successful publishing business on the Internet reveals the limitations of what was practical in May of 1994. Although digital works were being sold on the Internet, provisions for commerce were primitive. Furthermore, the ease of copying digital works had led many people to believe that digital information should be free. Fast access to the network had made trading programs or other data as easy as mixing songs on audio tape. In short, it had become much simpler for network users to infringe copyright than to uphold it. This is the context for the oft-quoted statement by John Perry Barlow of the Electronic Freedom Foundation, "Copyright is dead." Advocates of free information argue that because you don't lose the original when you make a copy of a digital work, there should be no charge for copying information. The conventional wisdom among publishers in late-1994, when this article was written, was that digital containers for software were inherently leaky vessels and that no viable solution would ever be found.

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Scatter/Gather is a cluster-based browsing technique for large text collections. Users are presented with automatically computed summaries of the contents of clusters of similar documents and provided with a method for navigating through these summaries at different levels of granularity. The aim of the technique is to communicate information about the topic structure of very large collections. We tested the effectiveness of Scatter/Gather as a simple pure document retrieval tool, and studied its effects on the incidental learning of topic structure. When compared to interactions involving simple keyword-based search, the results suggest that Scatter/Gather induces a more coherent conceptual image of a text collection, a richer vocabulary for constructing search queries, and communicates the distribution of relevant documents over clusters of documents in the collection.

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The Table Lens is a visualization for searching for patterns and outliers in multivariate datasets. It supports a lightweight form of exploratory data analysis (EDA) by integrating a familiar organization, the table, with graphical representations and a small set of direct manipulation operators. We examine the EDA process as a special case of a generic process, which we call sensemaking. Using a GOMS methodology, we characterize a few central EDA tasks and compare performance of the Table Lens and one of the best of the more traditional graphical tools for EDA i.e. Splus. This analysis reveals that Table Lens is more or less on par with the power of Splus, while requiring the use of fewer specialized graphical representations. It essentially combines the graphical power of Splus with the direct manipulation and generic properties of spreadsheets and relational database front ends. We also propose a number of design refinements that are suggested by our task characterizations and analyses.

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To facilitate users' ability to make sense of large collections of hypertext we present two new techniques for inducing clusters of related documents on the World Wide Web. Users' ability to find relevant information might also be enhanced by finding lawful properties of document behavior and use. We present models and analyses of document use and change for the World Wide Web.

An ecological-cognitive framework of analysis and a model-tracing architecture are presented and used in the analysis of data recorded from users browsing a large document collection. The users interacted with the Scatter/Gather browser, which clusters documents into groups of similar content and presents users with summaries of cluster content. Predictions made by a computational model of navigation and information foraging are matched against the observed activity.

Research on information visualization has reached the place where a number of successful point designs have been proposed and a number of techniques have been discovered. It is now appropriate to begin to describe and analyze portions of the design space so as to understand the differences among designs and to suggest new possibilities. This paper proposes an organization of the information visualization literature and illustrates it with a series of examples. The result is a framework for designing new visualizations and augmenting existing designs.

Clearly, the presentation method for information retrieved from the global information infrastructure (GII) makes a big difference to users. The NCSA Mosaic interface, for example, with its point-and-click multimedia page presentation, swelled popular interest in the World Wide Web. This experience suggests the possibility of increased usefulness if we apply visualization techniques to information retrieved from the GII. Note that, although the term "information visualization" is coming into use, the goal is really "information perceptualization." The latter implies a richer use of many senses, including sound and touch, to increase the rate at which people can assimilate and understand information. In discussing the visualization of retrieved information, it helps to consider four functional levels: (1) the infosphere, (2) the workspace, (3) sensemaking tools, and (4) the document. This simple classification lets us separate the functions served by the visualization from the techniques themselves, which can be applied across functional levels.

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(First paragraph): User interfaces, it has been said (Card, this volume), are an ineluctable part of interactive software systems. They are typically more than half the code, often far more. They typically cause more than half the problems, too - often far more. In short, they represent the sort of troublesome engineering problem that organizations would like to do something about.

This paper describes extensions to the Tioga flight-simulator browsing protocol presented by Stonebraker et al. (1993a). These extensions allow users to navigate a multidimensional data space using sophisticated zooming capabilities. This design also allows users to move easily between different multidimensional spaces. Tunneling between different data spaces is shown to be a substantial generalization of hyperlinks in a hypermedia system. Finally, our design provides for the coordination of multiple browsers. This preserves context and allows users to explore multiple paths simultaneously. In concert, these extensions incorporate the functionality of many information management paradigms as well as introducing new constructs. These powerful mechanisms for relating data provide users with great flexibility. For example, users can create magnifying glasses which show an enhanced view of the underlying data.

Buffering of intermediate results in dataflow diagrams can significantly reduce latency when a user browses these results or re-executes a diagram with slightly different inputs. We define the optimal buffer allocation problem of determining the buffer contents which minimize the average response time to such user requests. We show that this problem has several characteristics which render traditional latency reduction techniques ineffective. Since optimal buffer allocation is NP-hard, we propose heuristic methods for buffer management of intermediate results. We present a simulation of the behavior of these heuristics under a variety of conditions, varying graph structure and access pattern. We argue that history mechanisms which track user access patterns can be used to improve performance. We further show that graph structure and access pattern determine the factor of improvement which is possible. The performance enhancements we describe can be applied to minimize query response time in visual dataflow languages.

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Effective information access involves rich interactions between users and information residing in diverse locations. Users seek and retrieve information from the sources-for example, file servers, databases, and digital libraries and use various tools to browse manipulate, reuse, and generally process the information. We have developed a number of techniques that support various aspects of the process of user/information interaction. These techniques can be considered attempts to increase the bandwidth and quality of the interactions between users and information in an information workspace - an environment designed to support information work (see Figure 1).

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Information foraging theory is an approach to the analysis of human activities involving information access technologies. The theory derives from optimal foraging theory in biology and anthropology, which analyzes the adaptive value of food-foraging strategies. Information foraging theory analyzes trade-offs in the value of information gained against the costs of performing activity in human-computer interaction tasks. The theory is illustrated by application to information-seeking tasks involving a Scatter/Gather interface, which present users with a navigable, automatically computer overview of the contents of a document collection arranged as a cluster hierarchy.

This paper describes Butterfly, an Information Visualizer application for accessing DIALOG's Science Citation databases across the Internet. Network information often involves slow access that conflicts with the use of highly-interactive information visualization. Butterfly addresses this problem, integrating search, browsing, and access management via four techniques: 1) visualization supports the assimilation of retrieved information and integrates search and browsing activity, 2) automatically-created "link-generating" queries assemble bibliographic records that contain reference information into citation graphs, 3) asynchronous query processes explore the resulting graphs for the user, and 4) process controllers allow the user to manage these processes. We use our positive experience with the Butterfly implementation to propose a general information access approach, called Organic User Interfaces For Information Access, in which a virtual landscape grows under user control as information is accessed automatically.

A major effort in the Sequoia 2000 project was to build a very large database of earth science information. Without providing the means for scientists to efficiently and effectively locate required information and to browse its contents, however, this vast database would rapidly become unmanageable and eventually unusable. The Sequoia 2000 Electronic Repository addresses theses problems though indexing and retrieval software that is incorporated into the POSTGRES database management system. The Electronic Repository effort involved the design of probabilistic indexing and retrieval for text documents in POSTGRES, and the development of algorithms for automatic georeferencing of text documents and segmentation of full texts into topically coherent segments for improved retrieval. Various graphical interfaces support these retrieval features.

We present a new focus+context (fisheye) technique for visualizing and manipulating large hierarchies. Our technique assigns more display space to a portion of the hierarchy while still embedding it in the context of the entire hierarchy. The essence of this scheme is to lay out the hierarchy in a uniform way on a hyperbolic plane and map this plane onto a circular display region. This supports a smooth blending between focus and context, as well as continuous redirection of the focus. We have developed effective procedures for manipulating the focus using pointer clicks as well as interactive dragging, and for smoothly animating transitions across such manipulation. A laboratory experiment comparing the hyperbolic browser with a conventional hierarchy browser was conducted.

Biological sequence similarity analysis presents visualization challenges, primarily because of the massive amounts of discrete, multi-dimensional data. Genomic data generated by molecular biologists is analyzed by algorithms that search for similarity to known sequences in large genomic databases. The output from these algorithms can be several thousand pages of text, and is difficult to analyze because of its length and complexity. We developed and implemented a novel graphical representation for sequence similarity search results, which visually reveals features that are difficult to find in textual reports. The method opens new possibilities in the interpretation of this discrete, multi-dimensional data by enabling interactive investigation of the graphical representation.

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In [7] we proposed a visual programming system called Tioga. The Tioga system applies a boxes and arrows programming notation to allow nonexpert users to graphically construct database applications. Users connect database procedures using a dataflow model. Browsers are used to visualize the resulting data. This paper describes extensions to the Tioga Browser protocol. These extensions allow sophisticated, flight-simulator navigation through a multidimensional data space. This design also incorporates wormholes to allow tunneling between different multidimensional spaces. Wormholes are shown to be substantial generalizations of hyperlinks in a hypertext system. These powerful mechanisms for relating data provide users with great flexibility. For example, users can create magnifying glasses that provide an enhanced view of the underlying data.

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Although the document imaging industry has taken off in the last few years, document image filing for the individual information worker is still not widespread or effective. In this paper, we focus on building an electronic filing system for paper documents that supports the ad hoc, multifarious work of information workers. Motivated by interviews with researchers and a survey of descriptive studies of paper document filing, we have focussed on minimizing or delaying costs of document filing and supporting a rich variety of methods for accessing and using stored documents. We have implemented a prototype system called Protofoil for storing, retrieving, and manipulating paper documents as electronic images that integrates many user interface - paper and workstation - and information retrieval technologies. Protfoil has been tested through use in our laboratory, and has been deployed in a field study at a lawyer's office.

We present a new visualization, called the Table Lens, for visualizing and making sense of large tables. The visualization uses a focus+context (fisheye) technique that works effectively on tabular information because it allows display of crucial label information and multiple distal focal areas. In addition, a graphical mapping scheme for depicting table contents has been developed for the most widespread kind of tables, the cases-by -variables table. The Table Lens fuses symbolic and graphical representation into a single coherent view that can be fluidly adjusted by the user. This fusion and interactivity enables an extremely rich and natural style of direct manipulation exploratory data analysis.

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Increasing masses of information confronting a business or an individual have created a demand for information management applications. Time-based information, in particular, is an important part of many information access tasks. This paper explores how to use 3D graphics and interactive animation to design visualizers that improve access to large masses of time-based information. Two new visualizers have been developed for the Information Visualizer: 1) the Spiral Calendar was designed for rapid access to an individual's daily schedule, and 2) the Time Lattice was designed for analyzing the time relationships among the schedules of groups of people. The Spiral calendar embodies a new 3D graphics technique for integrating detail and context by placing objects in a 3D spiral. It demonstrates that advanced graphic techniques can enhance routine office information tasks. The Spiral Calendar development process involved three major phases: 1) progressive design based on our experience using advanced graphics for user interfaces, 2) an implementation/evaluation cycle based on a new method for characterizing information access from dynamic displays, and 3) reuse of the spiral technique for a decision support visualization where the spiral helps the user keep track of decisions while designing the layout of aircraft cockpit controls. The Time Lattice, on the other hand has only been informally evaluated. However, it illustrates how different tasks require different advanced graphics technology. In particular, the Time Lattice uses of 2D transparent shadows to provide interactive access to a complex 3D object. Our experience developing theses visualizations should prove useful to others developing user interface that use advanced graphics.

In this paper we present a method, the Cost-of-Knowledge Characteristic Function, for characterizing information access from dynamic displays. The paper works out this method for a simple, but important, class of dynamic displays called direct-walk interactive information visualizations, in which information is accessed through a sequence of mouse selections and key selections. The method is used to characterize a simple calendar task for an application of the Information Visualizer, to compute the changes in characterization as the result of possible program variants, and to conduct empirical comparison between different systems with the same function.

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Making sense of a body of data is a common activity in any kind of analysis. Sensemaking is the process of searching for a representation and encoding data in that representation to answer task-specific questions. Different operations during sensemaking require different cognitive and external resources. Representation are chosen and changed to reduce the cost of operations in an information processing task. The power of theses representational shifts is generally under-appreciated as is the relation between sensemaking and information retrieval. We analyze sensemaking tasks and develop a model of the cost structure of sensemaking. We discuss implications for the integrated design of user interfaces, representational tools, and information retrieval systems.

This paper describes a general visualization technique based on a common strategy for understanding paper documents when their structure is not known, which is to lay the pages of a document in a rectangular array on a large table where the overall structure and distinguishing features can be seen. Given such a presentation, the user wants to quickly view parts of the presentation in detail while remaining in context. A fisheye view or a magnifying lens might be used for this, but they fail to adequately show the global context. The Document Lens is a 3D visualization for large rectangular presentations that allows the user to quickly focus on a part of a presentation while continuously remaining in context. The user grabs a rectangular lens and pulls it around to focus on the desired area at the desired magnification. The presentation outside the lens is stretched to provide a continuous display of the global context. This stretching is efficiently implemented with affine transformations, allowing text documents to be viewed as a whole with an interactive visualization.

The goal of virtual reality systems is to place the user in a three-dimensional environment that can be directly manipulated. Ideally, users cease to think of themselves as interacting with a computer and interact instead with the 2D environment. The usual definition of VR involves full immersion. That is, users wear head-mounted stereo displays to provide full visual immersion and special gloves that allow six-degree-of-freedom input for directly manipulating the environment. An alternative form of VR is being explored in a number of research labs. Nonimmersive VR also places the user in a 3D environment that can be directly manipulated, but it does so with a conventional graphics workstation using a monitor, a keyboard, and a mouse. The scene is displayed with the same 3D depth cues used in immersive VR: perspective view, hidden-surface elimination, color texture, lighting, shading, and shadows. As in immersive VR, animation and simulation are interactively controlled in response to the user's direct manipulation. Much of the technology used to support immersive and nonimmersive VR is the same. They use the same 3D modeling and rendering and many of the same interaction techniques.

UI Innovations are often driven by a combination of technology advances and application demands. On the technology side, advances in interactive computer graphics hardware, coupled with low-cost mass storage, have created new possibilities for information retrieval systems in which UIs could play a more central role. On the application side, increasing masses of information confronting a business or an individual have created a demand for information management applications. In the 1980s, text-editing forced the shaping of the desktop metaphor and the now standard GUI paradigm. In the 1990s, it is likely that information access will be a primary force in shaping the successor to the desktop metaphor. This article presents an experimental system, the Information Visualizer (See Figure 1), which explores a UI paradigm that goes beyond the desktop metaphor to exploit the emerging generation of graphical personal computers and to support the emerging application demand to retrieve, store, manipulate, and understand large amounts of information. The basic problem is how to utilize advancing graphics technology to lower the cost of finding information and accessing it once found (the information's "cost structure").

Current information retrieval interfaces only address a small part of the reality of rich interactions amongst user, task and information sources. We view information gathering as an interactive, iterative activity involving multiple disparate information sources and embedded in the context of broader processes of information use. We have developed two key system components that enable information workspaces that adhere to this reformulation of information retrieval. The first is a design for a user/system interaction model for retrieval from multiple, disparate information sources. The second is a repository modeling system, called Repo, that represents meta-information about different information repositories in a manner that supports system operation as well as provides a direct information resource to the user. To test these ideas, we have utilized Repo and embodied the interaction model in the user interface of a system called Labrador.

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Since its invention millennia ago, paper has served as one of our primary communications media. Its inherent physical properties make it easy to use, transport, and store, and cheap to manufacture. Despite these advantages, paper remains a second class citizen in the electronic world. In this paper, we present a new technology for bridging the paper and electronic worlds. In the new technology, the user interface moves beyond the workstation and onto paper itself. We describe paper user interface technology and its implementation in a particular system called XAX.

(First paragraph of introduction): Over the last twenty years, computer science has developed rapidly as a discipline. As the content of computer science has continued to evolve and gain new substance, the curriculum of computer science has continually been revised to reflect the new content and deeper understandings of the nature of computers and information. This active reorganization is as would be expected for a new, vigorously developing discipline.

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Advances in computer technology have created new possibilities for information retrieval systems in which user interfaces could play a more central role. Our analysis of the problem suggests that what is needed from the user's point of view is not so much information retrieval itself, but rather, the amplification of information-based work processes. User interfaces enabled by this technology may be able to amplify work by modifying the cost structure of information used in work. As a consequence, we have attempted to go beyond the usual notion of an information retrieval systems to develop an "Information Workspace" that encompasses the cost structure of information from secondary storage to immediate use. As an implementation of the concept, we describe an experimental system, called the Information Visualizer, and its rationale. The system is based on the use of (1) 3D/Rooms for increasing the capacity of immediate storage available to the user, (2) an animated scheduler-based user interface interaction architecture, called the Cognitive Coprocessor, for coupling the user to information agents, and (3) information visualization for interacting with the information structure. The system and its rationale are described.

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The Information Grid (InfoGrid) is a framework for building information access applications that provides a user interface design and an interaction model. It focuses on retrieval of application objects as its top level mechanism for accessing user information, document, or services. We have embodied the InfoGrid design in an object-oriented application framework that supports rapid construction applications. This application framework has been used to build a number of applications, some that are classically characterized as information retrieval applications, others that are more typically viewed as personal work tools.

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One of the responsibilities of an intelligent interface is to design presentations of application information. An effective approach to this problem is to automatically search a space of possible designs. Since these design spaces are often large and complex, an important issue is how to control the search. This paper describes the search architecture used by the APT (A Presentation Tool) system for the automatic design of graphical presentations of relational information and discusses how it might be modified to handle more difficult design spaces.

The task of managing and accessing large information spaces is a problem in large scale cognition. Emerging technologies for 3D visualization and interactive animation offer potential solutions to this problem, especially when the structure of the information can be visualized. We describe one of these Information Visualization techniques, called the Cone Tree, which is used for visualizing hierarchical information structures. The hierarchy is presented in 3D to maximize effective use of available screen space and enable visualization of the whole structure. Interactive animation is used to shift some of the user's cognitive load to the human perceptual system.

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Tasks that involve large information spaces overwhelm workspaces that do not support efficient use of space and time. For example, case studies indicate that information often contains linear components, which can result in 2D layouts with wide, inefficient aspect rations. This paper describes a technique called Perspective Wall for visualizing linear information by smoothly integrating detailed and contextual views. It uses hardware support for 3D interactive animation to fold wide 2D layouts into intuitive 3D visualizations that have a center panel for detail and two perspective panels for context. The resulting visualization supports efficient use of space and time.

The market now contains a bewildering variety of input devices for communication from humans to computers. This paper discusses a means to systematize these devices through morphological design space analysis, in which different input device designs are taken as points in a parametrically described design space. The design space is characterized by finding methods to generate and test design points. In a previous paper, we discussed a method for generating the space of input device designs using primitive and compositional movement operators. This allowed us to propose a taxonomy of input devices. In this paper, we summarize the generation method and explore the use of device footprint and Fitts's law as a test. We then use calculations to reason about the design space. Calculations are used to show why the mouse is a more effective device than the headmouse and where in the design space there is likely to be a more effective device than the mouse.

This paper proposes a concept for the user interface of information retrieval system called an information workspace. The concept goes beyond the usual notion of an information retrieval system to encompass the cost structure of information from secondary storage to immediate use. As an implementation of the concept, the paper describes an experimental system, called the Information Visualizer, and its rationale. The system is based on (1) the use of 3D/Rooms for increasing the capacity of immediate storage available to the user, (2) the Cognitive Co-Processor scheduler-based user interface interaction architecture for coupling the user to information agent, and (3) the use of information visualization for interacting with information structure.

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A bewildering variety of devices for communication from humans to computers now exists on the market. In this article, we propose a descriptive framework for analyzing the design space of these input devices. We begin with Buxton's (1983) idea that input devices are transducers of physical properties in one, two, or three dimensions. Following Mackinlay's semantic analysis of the design space for graphical presentations, we extend this idea to more comprehensive descriptions of physical properties, space, and transducer mappings. In our reformulation, input devices are transducers of any combination of linear and rotary, absolute and relative, position and force, in any of the six spatial degrees of freedom. Simple input devices are described in terms of semantic mappings from the transducers of physical properties into the parameters of the applications. One of these mappings, the resolution function, allows us to describe the range of possibilities from continuous devices to discrete devices, including possibilities in between. Complex input controls are described in terms of hierarchical families of generic devices and in terms of composition operators on simpler devices. The description that emerges is used to produce a new taxonomy of input devices. The taxonomy is compared with previous taxonomies of Foley, Wallace, and Chan (1984) and of Buxton (1983) by reclassifying the devices previously analyzed by these authors. The descriptive techniques are further applied to the design of complex mouse-based virtual input controls for simulated three-dimensional (3D) egocentric motion. One result is the design of a new virtual egocentric motion control.

Computer graphics hardware supporting real-time interactive 3D animation has the potential to support effective user interfaces by enabling virtual 3D workspaces. However, this potential requires development of viewpoint movement techniques that support rapid and controlled movement through workspaces. Rapid movement through large distances avoids wasted work time; controlled movement near target objects allows the user to examine and interact with objects in the workspace. Current techniques for viewpoint movement typically use high velocities to cover distances rapidly, but high velocities are hard to control near objects. This paper describes a new technique for targeted viewpoint movement that solves this problem. The key idea is to have the user indicate a point of interest (target) on a 3D object and use the distance to this target to move the viewpoint logarithmically, by moving the same relative percentage of distance to the target on every animation cycle. The result is rapid motion over distances that slows as the viewpoint approaches the target object. The technique can be used with 2D and multidimensional input devices. We also extend the technologies to move objects in the workspace.

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A bewildering variety of devices for communication from humans to computers now exists on the market. In order to make sense of this variety, and to aid in the design of new input devices, we propose a framework for describing and analyzing input devices. Following Mackinlay's semantic analysis of the design space for graphical presentations, our goal is to provide tools for the generation and test of input device designs. The descriptive tools we have created allow us to describe the semantics of a device and measure its expressiveness. Using these tools, we have built a taxonomy of input devices that goes beyond earlier taxonomies of Buxton & Baecker and Foley, Wallace, & Chan. In this paper, we build on these descriptive tools, and proceed to the use of human performance theories and data for evaluation of the effectiveness of points in this design space. We focus on two figures of merit, footprint and bandwidth, to illustrate this evaluation. The result is the systematic integration of methods for both generating and testing the design space of input devices.

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The increasing availability of computers with high-quality graphics and fonts has created an opportunity and an obligation for user interface designers. The opportunity is that designers can use graphical techniques to design more effective user interfaces. The obligation is that they must become experts at the design of graphical user interfaces. Current user interface toolkits provide very little design assistance. This paper describes a theory that supports automatic design of graphical presentations of relational information and shows how to extend it to support theory-driven design of graphical users.

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An Interface is presented that is designed to help users switch among tasks on which they are concurrently working. Nine desirable properties for such an interface are derived. It is argued that a key constraint to building interfaces that support task switching is that low user-overhead switching among tasks required a large amount of display space, whereas actual display space is limited. A virtual workspace design is presented that greatly speeds the inevitable task-switching induced window faulting. The resulting interface is presented as a study in theory-based human-interface design. It is shown how in this case theory is important in inspiring a design, but design entailments outside the theory raise new issues that must be faced to make the design viable. These design experiences, in turn, help inspire new theory.

This paper presents the mail-order catalogue as a metaphor for the delivery of application software in an integrated work environment. It also describes, Catalogue, an adjunct to the Rooms multiple virtual workspace environment, which employs this metaphor. This mechanism can be used (1) to give users "instant starts" by letting the user's select a standard setup, (2) to allow users to assemble their own environment from standard components, (3) to parameterize a standard component, and (4) to load applications ready to run.

It can be argued that one of the chief impediments to progress in human engineering is the lack of a model of the human information-processor posed in such a way as to enable approximate engineering calculations to be made of human performance. The Model Human Processor is an attempt at such a model. The use of the model is illustrated through sample computations.

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The goal of the research described in this paper is to develop an application-independent presentation tool that automatically designs effective graphical presentations (such as bar charts, scatter plots, and connected graphs) of relational information. Two problems are raised by this goal: the codification of graphic design criteria in a form that can be used by the presentation tool, and the generation of a wide variation of designs so that the presentation tool can accommodate a wide variety of information. The approach described in this paper is based on the view that graphical presentations are sentences of graphical languages. The graphic design issues are codified as expressiveness and effectiveness criteria for graphical languages. Expressiveness criteria determine whether a graphical language can express the desired information. Effectiveness criteria determine whether a graphical language exploits the capabilities of the output medium and the human visual system. A wide variation of designs are systematically generated by using a "composition algebra" that composes a small set of primitive graphical languages. Artificial intelligence techniques are used to implement a prototype presentation tool called APT (A Presentation Tool), which is based on the composition algebra and the graphic design criteria.

A key constraint on the effectiveness of window-based human-computer interfaces is that the display screen is too small for many applications. This results in "window thrashing," in which the user must expend considerable effort to keep desired windows visible. Rooms is a window manager that overcomes small screen size by exploiting the statistics of window access, dividing the user's workspace into a suite of virtual workspaces with transitions among them. Mechanisms are described for solving the problems of navigation and simultaneous access to separated information that arise from multiple workspaces.

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Specialized languages are often more appropriate than general languages for expressing certain information. However, specialized languages must be chosen carefully because they do not allow all sets of facts to be stated. This paper considers the problems associated with choosing among specialized languages. Methods are presented for determining that a set of facts is expressible in a language, for identifying when additional facts are stated accidentally, and for choosing among languages that can express a set of facts. This research is being used to build a system that automatically chooses an appropriate graphical language to present a given set of facts.

Two experiments explored how users perform visual search to locate a target in a computer command menu. In Experiment 1, users searched for menu items while their eye movements were monitored. Visual search was well characterized by an unsystematic search model in which the user may search the same place more than once. This model predicted the distribution of search times, the lack of an item position effect, and the frequency of saccade directions. In Experiment 2, the unsystematic search model was used to describe the effects on search time of three menu-item arrangements and of practice. Initially, the arrangement of the menu, whether alphabetic, random, or categorical, influenced the time required by the search. But with practice, the user eventually learned the location of each item in the menu, rendering the arrangement of the menu unimportant.

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The use of text editors for writing original text has been little studied despite the importance of the task. A study conducted by Gould found that the composition rate of writers using a text editor was more than 50% slower than the same writers writing by hand. We show that the source of the slownenss is the design of the text editor and that using a display-oriented editor writers can write as fast and good typists faster than by hand. Like Gould, there was no quality difference based on the source of the letters and users of the text editor made many more modifications. Fewer than half of the modifications users made actually improved the text.

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