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

With the advent of high-speed networks, it is possible to build multimedia distributed applications that involve a geographically dispersed group of users. Development of such applications requires support for coordination and temporal synchronization of traffic over related streams. For instance, one must consider the problem of coordination in a multipoint communication where more than one sender may transmit data at the same time. Also, a multimedia application may need to synchronize traffic over multiple connections, each carrying traffic from a different medium. When a participant scrolls through an image browser (or a shared editor window) and says, "look at the middle of the display", the statement should be heard at the same time (or just after) the scrolling is completed. Such temporal relationships must be captured in the delivery of traffic over related flows. Existing transport and/or session layer protocols do not explicitly include communication abstractions t...

Current CSCW applications support one or more modes of cooperative work. The selection of and transition between these modes is usually placed on the users. We built the SEPIA cooperative hypermedia authoring environment supporting a complete set of situations arising during collaborative work and the smooth transitions between them. While early use of the system shows the benefits of supporting smooth transitions between different collaborative modes, it also reveals some deficits regarding parallel work, management of alternative documents, or reuse of document parts. We propose to integrate version support to overcome these limitations. This leads to a versioned data management and an extended user-interface enabling concurrent users to select a certain state of their work, to be aware of related changes, and to cooperate with others either asynchronously or synchronously.

DUPLEX is a distributed collaborative editor for users connected through the Internet. Large scale implies heterogeneity, unpredictable communication delays, and failures, and leads to inefficient implementations of techniques traditionally used for collaborative editing in local area networks. To cope with these unfavorable conditions, DUPLEX proposes a model based on splitting the document into independent parts, maintained individually and replicated by a kernel. Users act on document parts and interact with co-authors using a local environment providing a safe store and recovery mechanisms against failures or divergence with co-authors. Communication is reduced to a minimum, allowing disconnected operation. Atomicity, concurrency, and replica control are confined to a manageable small context. KEYWORDS: Collaborative editing, distributed groupware, large scale networks, concurrency control INTRODUCTION The past ten years have seen the number of interconnected computers and networ...

A great interest has developed in recent years in building tools that allow people to collaborate on work without the need for physical proximity. One such class of tools, group editors, allows collaborators to view and edit a shared document simultaneously from their workstations. Building group editors, however, requires solving non-trivial problems such as providing adequate response time for edit operations and yet ensuring consistency with concurrent updates, and providing adequate per-user undo facilities. We have implemented a toolkit, called DistEdit, for building new interactive group editors and for converting existing single-user editors into group editors with minimal changes to their code. The toolkit allows different users to use their favorite editors (e.g., Xedit, Gnu Emacs) to edit a shared file and observe each others ' changes as they occur. The toolkit provides fine-grain concurrency control, fault-tolerance, synchronization of views, and support for per-user undo. ...

Although talking is an integral part of collaboration, there has been little computer support for acqmrmg and accessing the contents of conversations. Our approach has focused on ubzquztous a udLo, or the unobtrusive capture of speech interactions in everyday work environments. Speech recognition technology cannot yet transcribe fluent conversational speech, so the words them-selves are not available for organizing the captured interactions. Instead, the structure of an interaction M derived from acoustical information inherent in the stored speech and augmented by user interaction during or after capture. This article describes apphcations for capturing and structuring audio from office discussions and telephone calls, and mechanisms for later retrieval of these stored interactions. An Important aspect of retrieval is choosing an appropriate visual representation, and this article describes the evolution of a family of representations across a range of applications. Finally, this work is placed within the broader context of desktop audio, mobde audio applications, and social implications.

We believe that virtual simulation of physical environments is an insufficient basis for building collaborative support systems. In response, we present a locales framework which frames collaboration as the interaction of individuals within social worlds regardless of whether that interaction is physical or virtual. The overview describes the five aspects of the framework: locale foundations, where locales are the basic structures providing the affordances for the work of social worlds; mutuality in interaction, including presence and awareness issues; individual views of multiple locales of interest, defined by the individual's participation in multiple social worlds; interaction trajectories, capturing the temporal dimensions of interaction; and civic structures, which embed locales and the collaborative work of groups in the larger public sphere. 1. Introduction Computer scientists in the Computer Supported Cooperative Work (CSCW) field are concerned with building systems to suppor...

The design of Computer-Supported Cooperative Work (CSCW) systems involves a variety of disciplinary approaches, drawing as much on sociological and psychological perspectives on group and individual activity as on technical approaches to designing distributed systems. Traditionally, these have been applied independently---the technical approaches focussing on design criteria and implementation strategies, the social approaches focussing on the analysis of working activity with or without technological support. However, the disciplines are more strongly related than this suggests. Technical strategies---such as the mechanisms for data replication, distribution and coordination---have a significant impact on the forms of interaction in which users can engage, and therefore on how their work proceeds. Consequently, the findings of sociological and psychological investigations of collaborative working have direct impact for how we go about designing collaborative systems. I...

this paper, we describe a paradigm and its associated collaboration artifact to allow flexible support for asynchronous collaboration. Under this paradigm, a user session with an application's user interface is encapsulated into a data artifact, referred to as a session object. Users collaborate by annotating, by modifying, and by a back-and-forth exchange of these session objects. Each session object is composed of several data streams that encapsulate audio annotations and user interactions with the application. The replay of a session object is accomplished by dispatching these data streams to the application for re-execution. Re-execution of these streams is kept synchronized to maintain faithfulness to the original recording. The basic mechanisms allow a participant who misses a session with an application to catch up on the activities that occurred during the session. This paper presents the paradigm, its applications, its design, and our preliminary experience with its use. Introduction

Real-time cooperative editing systems allow multiple users to view and edit the same document at the same time from multiple sites connected by a communication network. Consistency maintenance is one of the most significant challenges in designing and implementing real-time cooperative editing systems. In this paper, three inconsistency problems -- divergence, causality-violation, and intention-violation -- in real-time cooperative editing systems are first identified. Then, a novel consistency model, with properties of convergence, causality-preservation, and intention-preservation, is proposed as a framework for solving these problems. Moreover, an integrated set of schemes and algorithms, which support the proposed consistency model, are defined and discussed in detail. A software simulation system has been built to verify the correctness of the proposed approach. We conclude by summarizing the main results and contributions of this work and listing the major current and future work...