This paper examines the usability of the hypertext navigation facilities provided by World Wide Web client applications. A notation is defined to represent the user's navigational acts and the resultant system states. The notation is used to report potential, or `theoretical,' problems in the models of navigation supported by three web client applications. A usability study confirms that these problems emerge in actual use, and demonstrates that incorrect user models of the clients' facilities are common. A usability analysis identifies inadequacies in the clients' interfaces. Motivated by the analysis of usability problems, we propose extensions to the design of WWW client applications. These proposals are demonstrated by our system WebNetwhich uses dynamic graphical overview diagrams to extend the navigational facilities of conventional World Wide Web client applications. Related work on graphical overview diagrams for web navigation is reviewed. 1 Introduction The small...

It is important to provide a recovery operation for applications with a graphical user interface. A restricted linear undo mechanism can conveniently be implemented using object-oriented techniques. Although linear undo provides an arbitrarily long history, it is not possible to undo isolated commands from the history without undoing all following commands. Various undo models have been proposed to overcome this limitation, but they all ignore the problem that in graphical user interfaces a previous user action might not have a sensible interpretation in another state. The selective undo mechanism introduced here can undo isolated commands by copying them into the current state if that is meaningful. Furthermore, the semantics of selective undo are argued to be more natural for the user because the mechanism only looks at the command to undo and the current state and does not depend on the history in between. The user interface for selective undo can also be implemented generically. S...

this paper, we propose a general framework for implementing undo in collaborative systems. The framework allows users to individually reverse their own changes, taking into account the possibility of conflicts between different users' operations that may prevent an undo. The proposed framework has been incorporated into DistEdit, a toolkit for building group text-editors. Based on our experience with DistEdit's undo facilities, we discuss several issues that need to be taken into account in using the framework, in order to ensure that a reasonable undo behavior is provided to users. We show that the framework is also applicable to single-user systems, since the operations to undo can be selected not just on the basis of who performed them, but by any appropriate criterion, such as the document region in which the operations occurred or the time interval in which the operations were carried out. Categories and Subject Descriptors: D.2.2 [Software Engineering]: Tools and Techniques -- User Interfaces; H.1.2 [Models and Principles]: User/Machine Systems -- Human Factors; H.2.2 [Database

The ability to undo operations is a standard feature in most single-user interactive applications. However, most current collaborative applications that allow several users to work simultaneously on a shared document lack undo capabilities; those which provide undo generally provide only a global undo, in which the last change made by anyone to a document is undone, rather than allowing users to individually reverse their own changes. In this paper, we propose a general framework for undoing actions in collaborative systems. The framework takes into account the possibility of conflicts between different users' actions that may prevent a normal undo. The framework also allows selection of actions to undo based on who performed them, where they occurred, or any other appropriate criterion. KEYWORDS Undo, collaboration, groupware, conflict analysis. 1 INTRODUCTION The ability to undo operations is a standard and useful feature in most interactive single-user applications. For instance...

Claims have been proposed as a means of expressing HCI knowledge that is associated with a specific artefact and usage context. Claims describe design trade-offs and record HCI knowledge related to a specific design, or artefact, as psychological design rationale. Claims are created in the task-artefact cycle of interactive design and evaluation. Usability evaluation establishes a claim for a specific usage context, but this can restrict subsequent reuse of claims related knowledge. To widen the scope of reuse the knowledge contained within claims and their associated artefacts has to be classified and generalized. To address this problem a schema and method for classifying claims is introduced. The schema elaborates the description of HCI knowledge in claims and enables reuse by describing the assumptions and dependencies upon which a claim rests. Methods for generalising claims and discovering new claims from existing claims and artefacts were investigated. A factoring method for evolving child claims from parent claims and their usage scenarios is described. This employs a walkthrough technique based on Norman’s model of action with questions directed at the contributions a claim makes to usability at different stages in interaction. Factoring promotes evolution of child claims that either address different aspects of task support in the same domain as the parent claim, or development of more general child claims for user interface design. The relationships between claims are represented in maps to illustrate histories of task-artefact investigation that lead to claims evolution either via the factoring process or by empirical investigation. The schema and method for claims evolution are illustrated by case studies of claims development in tutoring systems and claims for functional requirements for specification reuse support tools. The paper concludes with a discussion of the contribution that reusable claims can make as a repository of HCI knowledge. 1 1.

Computer systems which can automatically alter aspects of their functionality or interface to suit the needs of individuals or groups of users have appeared over the years in a variety of guises. Most recently attention has focused on intelligent interface agents which are seen as specialised, knowledge-based systems acting on behalf of the user in some aspect of the interaction. Similar requirements for automatic adaptation have been noted in intelligent tutoring systems, natural language systems and intelligent interfaces. This paper brings together the research which has emanated from a number of backgrounds and provides a unifying perspective on adaptive systems in general. We present an architecture for adaptive systems and a methodology for their development. The paper also describes software support for producing adaptive systems and offers some experimental evidence to justify both the desirability and feasibility of exploiting an adaptive system approach to human-computer interaction.

Current practice in Human Computer Interaction as encouraged by educational institutes, academic review processes, and institutions with usability groups advocate usability evaluation as a critical part of every design process. This is for good reason: usability evaluation has a significant role to play when conditions warrant it. Yet evaluation can be ineffective and even harmful if naively done ‘by rule ’ rather than ‘by thought’. If done during early stage design, it can mute creative ideas that do not conform to current interface norms. If done to test radical innovations, the many interface issues that would likely arise from an immature technology can quash what could have been an inspired vision. If done to validate an academic prototype, it may incorrectly suggest a design’s scientific worthiness rather than offer a meaningful critique of how it would be adopted and used in everyday practice. If done without regard to how cultures adopt technology over time, then today's reluctant reactions by users will forestall tomorrow's eager acceptance. The choice of evaluation methodology – if any – must arise from and be appropriate for the actual problem or research question under consideration. Author Keywords Usability testing, interface critiques, teaching usability.

Abstract. In the two decades hand-held calculators have been readily available there has been ample time to develop a usable design and to educate the consumer public into choosing quality devices. This article reviews a representative calculator that is ‘state of the art’ and shows it has an execrable design. The design is shown to be confusing and essentially non-mathematical. Substantial evidence is presented that illustrates the inadequate documentation, bad implementation, feature interaction, and feature incoherence. These problems are shown to be typical of calculators generally. Despite the domain (arithmetic) being welldefined, the design problems are profound, widespread, confusing—and needless. Worrying questions are begged: about design quality control, about consumer behaviour, and about the role of education—both at school level (training children to acquiesce to bad design) and at university level (training professionals to design unusable products). The article concludes with recommendations. “The problem of efficient and uniform notations is perhaps the most serious one facing the mathematical public. ” Florian Cajori [5]. “[...] contrivances adapted to peculiar purposes [...] and what is worse than all, a profusion of notations (when we regard the whole science) which threaten, if not duly corrected, to multiply our difficulties instead of promoting our progress. ” Charles Babbage, quoted in [5]. 1

The design of theorem provers, especially in the LCF-prover family, has strongly profited from functional programming. This paper attempts to develop a metaphor suited to visualize the LCF-style prover design, and a methodology for the implementation of graphical user interfaces for these provers and encapsulations of formal methods. In this problem domain, particular attention has to be paid to the need to construct a variety of objects, keep track of their interdependencies and provide support for their reconstruction as a consequence of changes. We present a prototypical implementation of a generic and open interface system architecture, and show how it can be instantiated to an interface for Isabelle, called IsaWin, as well as to a tailored tool for transformational program development, called TAS.

Reflecting the growing consensus that principles and methods for developing effective interfaces are beginning to mature, usability design guidelines have begun to proliferate. But current approaches to guidelines tend to either be technology-centric, focusing on platform-specific interface widgets, or abstract and general-purpose. At best, these general guidelines provide weak support that is insufficient to support developers faced with specific interface design problems targeted for specific user populations. If the potential of usability guidelines as an interface design technique is to be fully realized, they need to be augmented with context-specific guidelines and examples that synthesize isolated guidelines into domain-specific solutions to design problems. In this paper, we present a method in which software development organizations can develop and evolve domain-specific guidelines based on the kinds of applications they develop. The method facilitates the process of determin...