Chengzheng Sun

Achieving convergence, causality preservation, and intention preservation in real-time cooperative editing systems

Real-time cooperative editing systems allow multiple users to view and edit the same text/graphic/image/multimedia document at the same time for multiple sites connected by communication networks. Consistency maintenance is one of the most significant challenges in designing and implementing real-time cooperative editing systems. In 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

Operational transformation in real-time group editors: issues, algorithms, and achievements

Rd-time group editors dow a group of users to view and edit, the same document at the same time horn geograpbicdy di.~ersed sites connected by communication networks. Consistency maintenance is one of the most si@cant &alwiges in the design and implementation of thwe types of systems. R=earch on rd-time group editors in the past decade has invented au inuolative tetique for consistency maintenance, ded operational transformation This paper presents an integrative review of the evolution of operational tra=formation techniques, with the go~ of identifying the major is-m~s, dgotiths, achievements, and remaining Mlenges. In addition, this paper contribut= a new optimized generic operational transformation control algorithm. Ke~vords Consistency maint enauce, operational transformation, convergence, CauS*ty pras~ation, intention pre~tion, group e&tors, groupware, distributed computing.

Transparent adaptation of single-user applications for multi-user real-time collaboration

Single-user interactive computer applications are pervasive in our daily lives and work. Leveraging single-user applications for supporting multi-user collaboration has the potential to significantly increase the availability and improve the usability of collaborative applications. In this article, we report an innovative Transparent Adaptation (TA) approach and associated supporting techniques that can be used to convert existing and new single-user applications into collaborative ones, without changing the source code of the original application. The cornerstone of the TA approach is the operational transformation (OT) technique and the method of adapting the single-user application programming interface to the data and operation models of OT. This approach and supporting techniques were developed and tested in the process of transparently converting two commercial off-the-shelf single-user applications (Microsoft Word and PowerPoint) into real-time collaborative applications, called CoWord and CoPowerPoint, respectively. CoWord and CoPowerPoint not only retain the functionalities and “look-and-feel” of their single-user counterparts, but also provide advanced multi-user collaboration capabilities for supporting multiple interaction paradigms, ranging from concurrent and free interaction to sequential and synchronized interaction, and for supporting detailed workspace awareness, including multi-user telepointers and radar views. The TA approach and generic collaboration engine software component developed from this work are potentially applicable and reusable in adapting a wide range of single-user applications.

Leveraging single-user applications for multi-user collaboration: the coword approach

Single-user interactive computer applications are pervasive in our daily lives and work. Leveraging single-user applications for multi-user collaboration has the potential to significantly increase the availability and improve the usability of collaborative applications. In this paper, we report an innovative transparent adaptation approach for this purpose. The basic idea is to adapt the single-user application programming interface to the data and operational models of the underlying collaboration supporting technique, namely Operational Transformation. Distinctive features of this approach include: (1) Application transparency: it does not require access to the source code of the single-user application; (2) Unconstrained collaboration: it supports concurrent and free interaction and collaboration among multiple users; and (3) Reusable collaborative software components: collaborative software components developed with this approach can be reused in adapting a wide range of single-user applications. This approach has been applied to transparently convert MS Word into a real-time collaborative word processor, called CoWord, which supports multiple users to view and edit any objects in the same Word document at the same time over the Internet. The generality of this approach has been tested by re-applying it to convert MS PowerPoint into CoPowerPoint.

Operational transformation for collaborative word processing

Operational Transformation (OT) is a technique originally invented for supporting consistency maintenance in collaborative text editors. Word processors have much richer data types and more comprehensive operations than plain text editors. Among others, the capability of updating attributes of any types of object is an essential feature of all word processors. In this paper, we report an extension of OT for supporting a generic Update operation, in addition to Insert and Delete operations, for collaborative word processing. We focus on technical issues and solutions involved in transforming Updates for both consistency maintenance and group undo. A novel technique, called Multi-Version Single-Display (MVSD), has been devised to resolve conflict between concurrent Updates, and integrated into the framework of OT. This work has been motivated by and conducted in the CoWord project, which aims to convert MS Word into a real-time collaborative word processor without changing its source code. This OT extension is relevant not only to word processors but also to a range of interactive applications that can be modelled as editors.

Generalizing operational transformation to the standard general markup language

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 SGMLs 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.

Flexible notification for collaborative systems

Notification is an essential feature in collaborative systems, which determines a systems capability and flexibility in supporting different kinds of collaborative work. In the past years, various notification strategies have been designed for different systems. However, the design of notification components has been ad hoc, and the techniques used for supporting notification have been application-dependent. In this paper, we contribute a flexible notification framework that can be used to describe and compare a range of notification strategies used in existing collaborative systems, and to guide the design of notification components for new collaborative systems. The framework has been applied to the design of a notification component for a group editor, which uses a single notification mechanism to support various notification policies for meeting both real-time and non-real-time collaboration needs. In addition, a new operational transformation control algorithm has been devised in combination with the notification component, which is significantly simpler and more efficient than existing algorithms.

Context-Based Operational Transformation in Distributed Collaborative Editing Systems

Operational Transformation (OT) is a consistency maintenance technique for collaborative editing systems-a special class of distributed applications for supporting human-computer-human interaction and collaboration over communication networks. The theory of causality has been the foundation of all prior OT systems, but it is inadequate to meet essential OT requirements in functionality and correctness. In this paper, we analyze the limitation of the causality theory, propose a novel theory of operation context as the new foundation for OT systems, and present a new OT algorithm-Context-based OT (COT)-which provides uniform and efficient solutions to both consistency maintenance and undo problems. The COT algorithm has been implemented and used for supporting a range of novel collaborative applications. The context theory and context vectors are potentially applicable to other distributed computing applications.

Undo any operation at any time in group editors

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 undopuzzles 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.

Real time cooperative editing on the Internet

New research and a prototype implementation solve some fundamental problems in distributed, real-time, cooperative editing in the Internet environment. The REDUCE systems strategies include a novel consistency model and responsiveness techniques that permit arbitrary order in executing independent operations.