Real-time group editors allow a group of users to view and edit the same document at the same time from geographically dispersed sites connected by communication networks. Consistency maintenance is one of the most significant challenges in the design and implementation of these types of systems. Research on real-time group editors in the past decade has invented an innovative technique for consistency maintenance, called operational transformation. This paper presents an integrative review of the evolution of operational transformation techniques, with the goals of identifying the major issues, algorithms, achievements, and remaining challenges. In addition, this paper contributes a new optimized generic operational transformation control algorithm. Keywords Consistency maintenance, operational transformation, convergence, causality preservation, intention preservation, group editors, groupware, distributed computing. INTRODUCTION Real-time group editors allow a group of users to ...

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

The ability to undo operations is an indispensable feature of real-time group editors, but supporting group undo is a difficult problem. None of the existing solutions for group undo is able to support undoing any operation at any time with guaranteed success. In this paper, we contribute a novel group undo solution with such a capability. The basic idea is to interpret an undo command as a concurrent inverse operation by means of operational transformation, so that an operation is always undoable regardless of its undo context. By separating undo policy from undo mechanism, multiple undo modes, such as single-step undo, chronological undo, and selective undo, can be supported in the same collaborative editing session. In addition, solutions to known undo puzzles are also provided. A web-based group text editor using the proposed undo solution has been implemented and is accessible at: http://reduce.qpsf.edu.au.

Abstract not found

The Distributed Operation Transform (dOPT), proposed by Ellis and Gibbs, is used to define concurrently updatable shared objects. Ellis and Gibbs give the operation transforms that define a simple shared text editor supporting single character insertions and deletions on a linear buffer. We report here on the construction of operation transforms for a more sophisticated groupware application: a shared spreadsheet. We identify a set of abstract operations that characterize the operations on a spreadsheet. Using Cormack's Calculus for Concurrent Update, which extends and corrects dOPT, we give the transforms on these operations necessary to define a shared spreadsheet. We use the transforms to build a shared version of sc, the Unix spreadsheet due to Gosling. KEYWORDS Groupware, Operation Transforms, Distributed Spreadsheets INTRODUCTION We are concerned with asynchronous distributed groupware, in which any copy of a replicated object can be updated at any time, and each update is the...

Publish-subscribe messaging middleware typically offers limited and low-level options for quality of service, such as best-effort delivery versus reliable delivery, or ordered versus unordered. We propose a new, high-level approach to specifying quality of service, in which the consumer specifies an event stream interpretation function that maps an event stream into a state that represents the consumer's semantics of the stream. Under this approach, the system may deliver either the subscribed event stream, or any alternative stream whose image under the interpretation function yields the same state. Event stream interpretation gives consumers the ability to more accurately specify the tolerable distortions of perfect message delivery, and gives middleware implementations the exibility to use more ecient protocols for message delivery and failure recovery while preserving application safety.

In this paper we extend operational transformation to support synchronous collaborative editing of documents written in dialects of SGML (Standard General Markup Language) such as XML and HTML, based on SGML’s abstract data model, the grove. We argue that concurrent updates to a shared grove must be transformed before being applied to each replica to ensure consistency. We express grove operations as property changes on positionally-addressed nodes, define a set of transformation functions, and show how to apply an existing generic operational transformation algorithm to achieve this. This result makes synchronous group editing applicable to the modern Web.

Abstract — In collaborative editing, consistency maintenance of the copies of shared data is a critical issue. In the last decade, Operational Transformation (OT) approach revealed as a suitable mechanism for maintaining consistency. Unfortunately, none of the published propositions relying on this approach are able to satisfy the mandatory correctness properties T P1 and T P2 defined in the Ressel’s framework. This paper addresses this correctness issue by proposing a new way to model shared state by retaining tombstones when elements are removed. An instantiation of the proposed model for a linear data structure and the related transformation functions are provided. I.

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...

Abstract. Research in collaborative editing tends to have been undertaken in isolation rather than as part of a general information or application infrastructure. Our goal is to develop a universal information platform that can support collaboration in a range of application domains. Since not all user groups have the same conventions and not all tasks have the same requirements, this implies that it should be possible to customize the collaborative editor at the level of both communities and individual tasks. One of the keys to customization is to use a structured rather than linear representation of documents that can be applied to both textual and graphical editors. In this paper, we propose the treeOPT (tree OPerational Transformation) algorithm that, relying on a tree representation of documents, applies the operational transformation mechanism recursively over the different document levels. Applications using this algorithm achieve better efficiency, the possibility of working at different granularity levels and improvements in the semantic consistency.