ing with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works, requires prior specific permission and/or a fee. Permissions may be requested from Publications Dept, ACM Inc., 1515 Broadway, New York, NY 10036 USA, fax 1 (212) 869-0481, or permissions@acm.org. ACM Transactions on Computer-Human Interactions, Vol.5, No.1, March 1998, Pages 63-108. 2 \Delta Chengzheng Sun, et al. 1. INTRODUCTION Cooperative editing systems are very useful groupware tools in the rapidly expanding areas of CSCW (Computer-Supported Cooperative Work) [Ellis et al. 1991], They can be used to allow physically dispersed people to edit a shared textual document [Ellis and Gibbs 1989

In real-time cooperative editing systems, independent operations on any part of the shared document may be generated from multiple cooperating sites. It is very important and technically challenging to ensure that the effect of executing an operation at remote sites, in the presence of concurrent execution of independent operations, achieves the same effect as executing this operation at the local site at the time of its generation, thus preserving its intention and maintaining system consistency. In this paper, we investigate the technical issues involved in preserving intentions of concurrent operations, explain the reasons why traditional serializationbased concurrency control strategies and existing operational transformation strategies failed to solve these problems, and propose a generic operation transformation scheme for intention preservation and consistency maintenance in real-time cooperative editing systems. The proposed scheme has been implemented in an Internetbased proto...

this paper has been partially supported by an NCGSS Grant from Griffith University and a Strategic Research Grant (Ref No:7000641) from City University of Hong Kong. Based on the REDUCE consistency model and concurrency control schemes, two Internet-based experimental REDUCE systems for both text and graphical editing have been developed using programming language Java. In this paper, we will discuss the generic parts of the REDUCE prototype systems, with focus on the system architecture and components (Section 2), and the distributed synchronization protocols among REDUCE components (Section 3). 2 SYSTEM ARCHITECTURE ANDCOMPONENTS

Abstract. We describe a new collaborative technology that bridges the gap between ad hoc collaboration in email and more formal collaboration in structured shared workspaces. Our approach is based on the notion of object-centric sharing, where users collaborate in a lightweight manner but aggregate and organize different types of shared artifacts into semi-structured activities with dynamic membership, hierarchical object relationships, as well as real-time and asynchronous collaboration. We present a working prototype that implements object-centric sharing on the basis of a replicated peer-to-peer architecture. In order to keep replicated data consistent in such a dynamic environment with blended synchronous and asynchronous collaboration, we designed appropriate consistency control algorithms, which we describe in detail. The performance of our approach is demonstrated by means of simulation results. Keywords: Object-centric sharing, replication, consistency control, peer-to-peer, activity-centric collaboration, synchronous and asynchronous collaboration. 1.

Research has focused significantly in enabling the Web (WWW) for Computer Supported Cooperative Work (CSCW). However, surfing, the most common use in the WEB, remains an individual, rather than group activity. Previous attempts to provide collaborative browsing capability constrain some users to the command of a selected user who controls the browsers of others. We adapt the technology of unconstrained distributed collaborative editors to develop unconstrained collaborative Web browsing. However, the effective collaboration is dependent on the awareness of context and group activity. We develop the history mechanisms for our solution to provide 4 types of awareness commonly discussed in the literature of CSCW. 1.

Real-time cooperative editing systems allows physically dispersed people to view and edit shared textual /graphical/multimedia documents at the same time. One of the most significant challenges in designing real-time cooperative editing systems is concurrency control under the constraints of a short response and notification time and unconstrained collaboration in distributed environments. This paper gives an overview of the major concurrency control issues in distributed real-time cooperative editing systems, and representative approaches to addressing them. Moreover, the concurrency control approach taken by our ongoing research project REDUCE (REal-time Distributed Unconstrained Cooperative Editing) is presented. Keywords: distributed computing, real-time cooperative editing, groupware, CSCW. 1 Introduction Real-time cooperative editing systems allows physically dispersed people to view and edit shared textual /graphical/multimedia documents at the same time [1, 8]. They are very ...

this article, a consistency model, with properties of convergence, causality preservation, and intention preservation, is proposed as a framework for consistency maintenance in real-time cooperative editing systems. Moreover, an integrated set of schemes and algorithms, which support the proposed consistency model, are devised and discussed in detail. In particular, we have contributed (1) a novel generic operation transformation control algorithm for achieving intention preservation in combination with schemes for achieving convergence and causality preservation and (2) a pair of reversible inclusion and exclusion transformation algorithms for stringwise operations for text editing. An Internet-based prototype system has been built to test the feasibility of the proposed schemes and algorithms