We describe a large scale, low cost, project that has examined the way people develop their skill in using fundamental software tools. The study involved over two thousand users during a three-year period of use of the sam text editor. The work took place while the editor was being employed in normal day to day work - it was not a laboratory experiment. Our main contributions are first to demonstrate very long-term, low-cost monitoring with collections of simple analysis tools. Second, we have started to develop an understanding of how usability changes in the long term. Third, studies of usability often concentrate on assessment before a system is released for widespread use, whereas ours can help inform the long term design of new tools - a different dimension of usability. In addition we have mixed snap-shot studies with descriptions of long-term, gradual change. We can track the full development of the user, even though the quality of the data is lower than that normally ...

Remote access feels different from local access. The major issues are consistency (machines vary in GUIs, applications, and devices) and responsiveness (the user must wait for network and server delays). Protium attacks these by partitioning programs into local viewers that connect to remote services using application-specific protocols. Partitioning allows viewers to be customized to adapt to local features and limitations. Services are responsible for maintaining long-term state. Viewers manage the user interface and use state to reduce communication between viewer and service, reducing latency whenever possible. System infrastructure sits between the viewer and service, supporting replication, consistency, session management, and multiple simultaneous viewers. The prototype system includes an editor, a draw program, a PDF viewer, a map database, a music jukebox, and windowing system support. It runs on servers, workstations, PCs, and PDAs under Plan 9, Linux, and Windows

It is difficult to build user interfaces that must be distributed over a set of dynamic and heterogeneous I/O devices. This difficulty increases when we want to split, merge, replicate, and relocate the UI across a set of heterogeneous devices, without the application intervention. Furthermore, using generic tools, e.g. to search for UI compoments or to save/restore them, is usually not feasible. We follow a novel approach for building UIs that overcomes these problems: Using distributed file systems that export widgets to applications. In this paper we describe Omero, a UI server built along this line for the Plan B Operating System.

The continuing micro-miniaturization of components has moved high-powered, microprocessor-based machines from the desktop, to the laptop, to notebook-sized, and now to palmtop computers. These machines are distinguished in their hardware technology, but supporting software has not kept pace: the predominant operating system on such machines is MS-DOS, absent integrated support for distributed computing. With the LITTLE WORK project, I propose to close this gap in the information technology environment. The LITTLE WORK prototype will be a notebook computer well-endowed with memory and local disk. It will run the Mach operating system and an AFS cache manager, operating predominantly in a dataless mode. The network interface will be the serial port, attached to a fixed or cellular phone attached to a high-speed modem. To economize on limited network bandwidth and substantial cellular phone charges, AFS will be engineered to support compressed headers and to operate in a disconnected mode...

Commercial UNIX window systems are unsatisfactory. Because they are cumbersome and complicated, they are unsuitable companions for an operating system that is appreciated for its technical elegance. Their clumsy user interfaces clutter the view of the operating system. A good interface should clarify the view, not obscure it. Mux is one window system that is popular and therefore worth studying as an example of good design. (It is not commercially important because it runs only on obsolete hardware.) This paper uses mux as a case study to illustrate some principles that can help keep a user interface simple, comfortable, and unobtrusive. When designing their products, the purveyors of commercial window systems should keep these principles in mind. Introduction Mux is a window system with no icons, no help facility, no customizability, no noise, and only two menus (one with five entries, one with seven). The spareness of its user interface distinguishes it from commercial window system...

Garbage collection algorithms rely on invariants to permit the identification of pointers and to correctly locate accessible objects. These invariants translate into constraints on object layouts and programming conventions governing pointer use. There are recent variations of collectors in which the invariants are relaxed. Typically, rules governing pointer use are relaxed, and a ‘conservative ’ collection algorithm that treats all potential pointers as valid is used. Such pointers are ‘ambiguous ’ because integers and other data can masquerade as pointers. Ambiguous pointers cannot be modified and hence the objects they reference cannot be moved. Consequently, conservative collectors are based on mark-andsweep algorithms. Copying algorithms, while more efficient, have not been used because they move objects and adjust pointers. This paper describes a variation of a copying garbage collector that can be used in the presence of ambiguous references. The algorithm constrains the layout and placement of objects, but not the location of referencing pointers. It simply avoids copying objects that are referenced directly by ambiguous pointers, reclaiming their storage on a subsequent collection when they are no longer ambiguously referenced. An implementation written in the ANSI C programming language is given.

This paper addresses the problems and opportunities for continuous learning in the workplace. The domain is text processing where the primary means of long term development is based on user initiative: exploring, reading manuals and learning from other users. The study is large scale: it ran for three years and involved a total of over two thousand users. A smaller group of users is examined in detail. It demonstrates that significant learning occurs over the very long term. We identify the importance of the problem of scale. The gross profile suggests that most learning occurs very early and that is the main feature. However, the detailed profile shows important variations over the full three years. For long term learning in the workplace, users have to be empowered to draw on the resources around them at times that suit themselves. Essential to the provision of suitable resources is a clear understanding of the long term process of learning in the workplace. It is this basis that our work provides. CR categories and subject descriptors:

Introduction Ded is a text display editor designed by computer scientists. The design is characterised by simplicity and adherence to user interface principles. This has led to a good design but with contentious features. This chapter highlights the conflict between principles and features, particularly in the social context in which ded was designed. The primary intent of this chapter is to present the context and design decisions lying behind a particular interactive system. Neither the design itself nor its description here has been directly influenced by the book's framework; it seems more honest that way. However, the following salient points may be noted: . Science is considered as a form of explicit, public knowledge. The public (i.e., user) accessibility of explanation of ded was a criterion of satisfactory design. As designers we also explained ded to ourselves by way of principles; thus, the role of principles was paramount, as we hope will be made clear in this chapter.

The data structure used ot maintain the sequence of characters is an important part of a text editor. This paper investigates and evaluates the range of possible data structures for text sequences. The ADT interface to the text sequence component of a text editor is examined. Six common sequence data structures (array, gap, list, line pointers, fixed size buffers and piece tables) are examined and then a general model of sequence data structures that encompasses all six structures is presented. The piece table method is explained in detail and its advantages are presented. The design space of sequence data structures is examined and several variations on the ones listed above are presented. These sequence data structures are compared experimentally and evaluated based on a number of criteria. The experimental comparison is done by implementing each data structure in an editing simulator and testing it using a synthetic load of many thousands of edits. We also report on experiments on t...

We describe the use of database dependency theory for investigating software designs. Dependency theory captures some of the essential constraints implicit in a system, and focuses attention on its update properties. The fundamental choice between redundancy and normalization is directly related to the issue of reuse. We show how dependency theory can be applied to the design of text editors and spreadsheet systems, and discuss