Scalar topology in the form of Morse theory has provided computational tools that analyze and visualize data from scientific and engineering tasks. Contracting isocontours to single points encapsulates variations in isocontour connectivity in the Reeb graph. For multivariate data, isocontours generalize to fibers-inverse images of points in the range, and this area is therefore known as fiber topology. However, fiber topology is less fully developed than Morse theory, and current efforts rely on manual visualizations. This paper presents how to accelerate and semi-automate this task through an interface for visualizing fiber singularities of multivariate functions R³ → R². This interface exploits existing conventions of fiber topology, but also introduces a 3D view based on the extension of Reeb graphs to Reeb spaces. Using the Joint Contour Net, a quantized approximation of the Reeb space, this accelerates topological visualization and permits online perturbation to reduce or remove degeneracies in functions under study. Validation of the interface is performed by assessing whether the interface supports the mathematical workflow both of experts and of less experienced mathematicians.

Contour Trees and Reeb Graphs are firmly embedded in scientific visualization for analysing univariate (scalar) fields. We generalize this analysis to multivariate fields with a data structure called the Joint Contour Net that quantizes the variation of multiple variables simultaneously. We report the first algorithm for constructing the Joint Contour Net, and demonstrate some of the properties that make it practically useful for visualisation, including accelerating computation by exploiting a relationship with rasterisation in the range of the function.

Contour trees and Reeb graphs are firmly embedded in scientific visualization for analysing univariate (scalar) fields. We generalize this analysis to multivariate fields with a data structure called the Joint Contour Net that quantizes the variation of multiple variables simultaneously. We report the first algorithm for constructing the Joint Contour Net and demonstrate that Contour Trees for individual variables can be extracted from the Joint Contour Net.

Profiling real-world Haskell programs is hard, as compiler optimizations make it tricky to establish causality between the source code and program behavior. In this paper we attack the root issue by performing a causality analysis of functional programs under optimization. We apply our findings to build a novel profiling infrastructure on top of the Glasgow Haskell Compiler, allowing for performance analysis even of aggressively optimized programs.

In nuclear science, density functional theory (DFT) is a powerful tool to model the complex interactions within the atomic nucleus, and is the primary theoretical approach used by physicists seeking a better understanding of fission. However DFT simulations result in complex multivariate datasets in which it is difficult to locate the crucial `scission' point at which one nucleus fragments into two, and to identify the precursors to scission. The Joint Contour Net (JCN) has recently been proposed as a new data structure for the topological analysis of multivariate scalar fields, analogous to the contour tree for univariate fields. This paper reports the analysis of DFT simulations using the JCN, the first application of the JCN technique to real data. It makes three contributions to visualization: (i) a set of practical methods for visualizing the JCN, (ii) new insight into the detection of nuclear scission, and (iii) an analysis of aesthetic criteria to drive further work on representing the JCN.

Service-oriented architectures are increasingly being used as the architectural style for creating large distributed computer applications. This paper examines the provision of visualization as a service that can be made available to application designers in order to combine with other services. We develop a three-layer architecture: a client layer which provides the user interface; a stateful Web service middleware layer which provides a published interface to the visualization system; and finally, a visualization component layer which provides the core functionality of visualization techniques. This separation of middleware from the visualization components is crucial: it allows us to exploit the strengths of Web service technologies in providing standardized access to the system, and in maintaining state information throughout a session, but also gives us the freedom to build our visualization layer in an efficient and flexible way without the constraints of Web service protocols. We describe the design of a visualization service based on this architecture, and illustrate one aspect of the work by re-visiting an early example of Web-based visualization.

The pipeline model in visualization has evolved from a conceptual model of data processing into a widely used architecture for implementing visualization systems. In the process, a number of capabilities have been introduced, including streaming of data in chunks, distributed pipelines, and demand-driven processing. Visualization systems have invariably built on stateful programming technologies, and these capabilities have had to be implemented explicitly within the lower layers of a complex hierarchy of services. The good news for developers is that applications built on top of this hierarchy can access these capabilities without concern for how they are implemented. The bad news is that by freezing capabilities into low-level services expressive power and flexibility is lost. In this paper we express visualization systems in a programming language that more naturally supports this kind of processing model. Lazy functional languages support fine-grained demand-driven processing, a natural form of streaming, and pipeline-like function composition for assembling applications. The technology thus appears well suited to visualization applications. Using surface extraction algorithms as illustrative examples, and the lazy functional language Haskell, we argue the benefits of clear and concise expression combined with fine-grained, demand-driven computation. Just as visualization provides insight into data, functional abstraction provides new insight into visualization.

The purpose of visualization is not just to depict data, but to gain or present insight into the domain represented in data. However in visualization systems, this link between features in the data and the meaning of those features is often missing or implicit. It is assumed that the user, through looking at the output, will close the loop between representation and insight. An alternative is to view visualization tools as interfaces between data and insight, and to enrich this interface with capabilities linked to users’ conceptual models of the data. Preliminary work has been carried out to develop such an interface as a modular component that can be installed in a pipelined architecture. This poster expands the motivation for this work, and describes the initial implementation carried out within the Visualization Toolkit (VTK).

Recent activity within the UK National e-Science Programme has identified a need to establish an ontology for visualization. Motivation for this includes defining web and grid services for visualization (the ‘semantic grid’), supporting collaborative work, curation, and underpinning visualization research and education. At a preliminary meeting, members of the UK visualization community identified a skeleton for the ontology. We have started to build on this by identifying how existing work might be related and utilized. We believe that the greatest challenge is reaching a consensus within the visualization community itself. This poster is intended as one step in this process, setting out the perceived needs for the ontology, and sketching initial directions. It is hoped that this will lead to debate, feedback and involvement across the community.

Abstract Previous studies at the intersection between rendering and psychology have concentrated on issues such as realismand acuity. Although such results have been useful in informing development of realistic rendering techniques,studies have shown that the interpretation of images is influenced by factors that have little to do with realism. Inthis paper, we summarize a series of experiments, the most recent of which are reported in a separate paper, thatinvestigate affective (emotive) qualities of images. These demonstrate significant effects that can be utilized withininteractive graphics, particularly via non‐photorealistic rendering (NPR). We explain how the interpretation ofthese results requires a high‐level model of cognitive information processing, and use such a model to account forrecent empirical results on rendering and judgement. Categories and Subject Descriptors (according to ACM CCS): I.3.m [Computer Graphics]: Miscellaneous

There are many toolkits and development environments that aid the process of constructing virtual environment applications. Many of these development environments encourage customising a virtual environment's design while rapid prototyping within the confines of a toolkit's capabilities. Thus the choice of the technology and its associated support has been made independent of the end‐use requirements of the final system. This can bias a virtual environment's design by implementation based constraints. We propose that an alternative approach is the consideration of virtual environment requirements in the context of an inspectable design model, to identify the requirements that a toolkit will need to support. In the context of an example, we present a selection of design requirements that we consider important for virtual environment design in general. We explore how these requirements might be mapped to different capabilities using Virtual Reality Modelling Language (VRML) as a concrete example of a platform technology.

Abstract. Much of the behaviour of an interactive system is determined by its user population. This paper describes how assumptions about the user can be brought into system models in order to reason about their behaviour. We describe a system model containing reasonable assumptions about the user as being ‘cognitively plausible’. Before asserting the plausibility of a model however we must first be able to make the assumptions made in that model inspectable. There is a tension between the inspectability of user assumptions and the tractability of models; inspectable models tend to not be very tractable and vice versa . We describe how we can get round this tension, by deriving tractable models from explicit user assumptions. The resulting models may not of themselves be very inspectable to human-factors workers, but the process by which they are derived is inspectable. Hence we claim that we can have both tractability and inspectability. We exemplify our claims using a simple cognitive model and ‘Meeting Maker’, an interactive electronic diary system.

A significant proportion of early HCI research was guided by one very clear vision: that the existing theory base in psychology and cognitive science could be developed to yield engineering tools for use in the interdisciplinary context of HCI design. While interface technologies and heuristic methods for behavioral evaluation have rapidly advanced in both capability and breadth of application, progress toward deeper theory has been modest, and some now believe it to be unnecessary. A case is presented for developing new forms of theory, based around generic “systems of interactors.” An overlapping, layered structure of macro- and microtheories could then serve an explanatory role, and could also bind together contributions from the different disciplines. Novel routes to formalizing and applying such theories provide a host of interesting and tractable problems for future basic research in HCI.

Much of the work concerned with virtual environments has addressed the development of new rendering technologies or interaction techniques. As the technology matures and becomes adopted in a wider range of applications, there is, however, a need to better understand how this technology can be accommodated in software engineering practice. A particular challenge presented by virtual environments is the complexity of the interaction that is supported, and sometimes necessary, for a particular task. Methods such as finite‐state automata which are used to represent and design dialogue components for more conventional interfaces, e.g. using direct manipulation within a desktop model, do not seem to capture adequately the style of interaction that is afforded by richer input devices and graphical models. In this paper, we suggest that virtual environments are, fundamentally, what are known as hybrid systems. Building on this insight, we demonstrate how techniques developed for modelling hybrid systems can be used to represent and understand virtual interaction in a way that can be used in the specification and design phases of software development, and which have the potential to support prototyping and analysis of virtual interfaces.

Abstract. Many of the reported experiences in the industrial use of formal methods concern the development of products or product families, where the utility of the method is linked to direct savings in development costs or improved assurance of quality. However, one other area in which formal description techniques make a valuable contribution is in the development and documentation of International Standards, where the cost of using formal methods can be paid off both through increased quality of products that implement a given standard, and through the improved inter-operability of different implementations that comes from having a precise definition of the expected behaviour of a conforming implementation. Standards development, however, has some significant differences from product development, and comes with specific needs and constraints that affect the use of formal description techniques. This paper describes the role that formal methods played in the development of a new standard for distributed multimedia presentation. It describes a number of issues that arose from this experience, and which have longer term importance for formal methods in standards, particularly given the changes that are taking place in the way that standards are developed.

Abstract. Software systems are not just mathematical structures. The majority are also cognitive artefacts that rely on the ability of their users to understand and interpret information provided via an interface, and to act on that information using actions provided by the system. The design of an interactive system must thus account for both the technical requirements of the given domain, and the cognitive abilities of the user. However, the disciplines involved (computer science and psychology) traditionally operate with quite different methods and techniques, making it difficult to integrate their respective insights into system design. This paper reports on work that is creating a framework for interaction that encompasses both the description of complex software systems and the cognitive resources needed to operate those systems. An interface for supporting gestural interaction is used to illustrate the approach. The paper concludes with an assessment of the prospects for this kind of integrative modeling and sets out key areas for future progress.

Abstract. There is considerable interest within the Human Computer Interaction (HCI) community in the use of media spaces to enhance awareness and interaction between workers in offices or other spatially distributed environments. In addition to the technical challenges of providing reliable and efficient audio-visual communication, there are important social questions, in particular how users are able to control access to their personal environments, and how to advise other users about their level of availability. Within AMODEUS-2 1 , an ESPRIT Basic Research Action concerned with the development, transfer and assessment of techniques for modelling human-computer interaction, a prototype media space has been analysed by various user and system oriented modelling techniques. This paper describes how formal specification can be used to express requirements on the interfaces needed to control access and availability in a media space. Beyond its obvious use in clarifying the subtle relationship between these concerns, the paper describes how the specification assists in assessing design options originating from other modelling disciplines.

msTRAcT Advmees in hardware, software, and coding stindards for digiti media have now made the defivery of mdtimedia ifiormation a sWdard component of many systems.Unfortunately, the pace of this technologiml development coupled Itith strong commercial competition between leadng vendors, has meant that fittle consensus hx emerged over the dwign of programming interfaces to Wow the creation, maniptiation, ~d presentation of such dab.PREMO &Resentition Environments for Mtitimedia Objeck) is a new MO S*dard, to be pub-~~bed in 1998, that defies a middeware frmework encompassing synchrotiation, the mnagement of distributed media resourcw, and the sdess integration of dab and processw from d~parate appti~tion areas.This paper @ves m ove~ew of the concepts under-l~ting PREMO and the approach by which the shndard ut~ies these concepts to addrws key mpeck of mtitirnedia systems design.1.1

Of the various programming paradigms in use today, object‐orientation is probably the most successful in terms of industrial take‐up and application, particularly in the field of multimedia. It is therefore unsurprising that this technology has been adopted by ISO/IEC JTC1/SC24 as the foundation for a forthcoming International Standard for Multimedia, called PREMO. Two important design aims of PREMO are that it be distributable, and that it provides a set of media‐related services that can be extended in a disciplined way to support the needs of future applications and problem domains. While key aspects of the object‐oriented paradigm provide a sound technical basis for achieving these aims, the need to balance extensibility and a high‐level programming interface against the realities of efficiency and ease of implementation in a distributed setting meant that the task of synthesising a Standard from existing practice was non‐trivial. Indeed, in order to meet the design aims of PREMO is was found necessary to augment the basic object infrastructure with facilities and ideas drawn from other programming paradigms, in particular concepts from constraint management and data flow. This paper describes the important trade‐offs that have affected the development of PREMO and explains how these are addressed through the use of specific programming paradigms.

User and system models typically are viewed as independent representations that provide complementary insights into aspects of human-computer interaction. Within system development, it is usual to see the 2 activities as separate, or at best loosely coupled, with either the design artifact or some third "mediatiag" expression providing the context in which the results of modelling can be related. This article proposes that formal system models can be combined directly with a representation of human cognition to yield an integrated view of human-system interaction: a syndetic model. Aspects of systems that affect usability then can be described and understood in terms of the conjoint behavior of user and computer. This article introduces and discusses, in syndetic terms, 2 scenarios with markedly different properties. We show how syndesis can provide a formal foundation for reasoning about interaction.

Certain design projects raise difficult user-interface problems that are not easily amenable to designers' intuition or rapid prototyping due to their novelty, conceptual complexity, and the difficulty of conducting appropriate user studies. Interpersonal access control in computer-mediated communication (CMC) systems is just such a problem. We describe a collection of systematic theory-based analyses of a system prototype that inherited its control mechanism from two preexisting systems. We demonstrate that the collective use of system and user modeling techniques provides insight into this complex design problem and enables us to examine the implications of design decisions for users and implementation. The analyses identify a number of weaknesses in the prototype and are used to propose ways of making substantive refinements to improve its simplicity and appropriateness for two tasks: altering one's accessibility and distinguishing between who can make what kinds of connections. We conclude with a discussion of some critical issues that are relevant for CMC systems, and reflect on the process of applying formal human-computer interaction (HCI) techniques in informal, exploratory design contexts.

The problem of developing software to meet precise specifications has lead to the development of mathematical notations for expressing and reasoning about the behaviour of a required or extant system. We describe a different use of formal models: as tools for gathering and consolidating requirements on interaction between engineered systems and their users. This change in focus reflects the growing use of sophisticated interactive technology in domains such as medicine, where human comfort or safety is an issue. Not only must software systems function correctly, but the demands that the interface places on users of those systems need to be understood. This problem cannot be addressed by formal models in isolation. Instead, we describe an approach that uses formal models of human information processing to augment models of system functions. As a result it becomes possible, at an early stage in system design, to consider the role of human cognition in the correct behaviour of the system.

Abstract Many of the reported developments in the design of virtual spaces or visualisation systems are based on improvements in technology, either physical devices or algorithms for achieving realistic renderings within real‐time constraints. While this experimental approach produces a wealth of empirical results, it operates largely without a sound underlying theory that can be used to design systems that will effectively support users in real‐world domains. One of the main problems is that these sophisticated technologies rely on, but rarely assess, the cognitive abilities of the user. This paper introduces a new approach to modelling human‐system interaction. A syndetic model combines a formal expression of system behaviour with an approximate representation of cognitive resources to allow reasoning about the flow and utilisation of information within the combined system. The power of the approach to provide insight into novel interaction techniques is illustrated by developing a syndetic model of a gesture‐driven user interface.

Abstract Many descriptions of multimedia programming systems are starting to appear in the literature, but little work has yet been done on how to formally specify and reason about such systems. This paper is a contribution on the use of formal description techniques for the specification of multimedia systems and explores a style in which the Object‐Z notation from the University of Queensland can be used to specify some of the properties and functionality of such systems. The work has been carried out with reference to the role of formal description techniques in the presentation of ISO/IEC International Standards and in particular to the Premo project in ISO/IEC JTCl/SC24.

Abstract The concept of an ‘interactor’ has been introduced by Faconti and Paterno' [6] as an abstraction of an entity in interactive graphics capable of both input and output. However the notion of interaction object need not be confined to graphics systems; it represents a useful structure for thinking and reasoning about the behaviour of interactive systems in general. As part of Esprit Basic Research Action 7040 (Amodeus‐2) we are using the concept of interactor, and existing work on state‐based processes and agents, to develop a model and theory of interactive systems. In this paper we describe two formal models for interaction objects and sketch how they can be used to build a small vocabulary of operators to support the rigorous specification of a graphics system. Our model differs from the approach of Faconti and Paterno' in that it abstracts away from any specific graphics framework and is thus suited to the level of abstraction demanded by formal approaches to system development.