Group editors allow a distributed group of users to collaboratively edit shared documents such as source code and web pages. As a well-accepted consistency control method in group editors, operational transformation (OT) is intuitively believed to be able to preserve operation intentions. However, intention preservation as a consistency constraint has not been rigorously formalized, making it difficult to design OT algorithms and prove their correctness. This work proposes a formalization of intention preservation and analyzes several OT-based approaches to achieving it.

Group editors allow a group of distributed human users to edit a shared multimedia document at the same time over a computer network. Consistency control in this environment must not only guarantee convergence of replicated data, but also attempt to preserve intentions of operations. Operational transformation (OT) is a well-established method for optimistic consistency control in this context and has drawn continuing research attention since 1989. However, counterexamples to previous works have often been identified despite the significant progress made on this topic over the past 15 years. This paper analyzes the root of correctness problems in OT and establishes a novel operational transformation framework for developing OT algorithms and proving their correctness.

Commutativity of operations is often exploited in concurrent systems to attain high levels of concurrency. A commutativity-based concurrency control method, called operational transformation (OT), has been actively researched in groupware over the past 15 years. However, much progress can still be made on more practicable approaches to developing and proving OT algorithms. Several constraints have been proposed previously but they are generally difficult to follow and verify in practice. This paper proposes an alternative approach to address this problem. A new consistency model is defined which greatly simplifies the design and proof of OT algorithms.

Operational transformation (OT) is a responsive and nonblocking concurrency control method widely-accepted in group editors. Correctness and performance are the basis of usefulness and usability of OT-based group editors. However, the correctness of previous OT algorithms depends on conditions that are very difficult to verify. In this paper we propose a novel landmark-based transformation (LBT) approach, its correctness no longer depending on those conditions and thus easy to prove. In addition, we give an example algorithm that significantly outperforms a state-of-the-art OT algorithm. This work reveals a more practical approach to developing OT algorithms.

Consistency maintenance is a critical and challenging issue in many interactive groupware applications that can be modeled as group editors. This paper addresses two open consistency problems: divergence and operation effects relation violation. While the former has been partly solved, the latter has never been addressed in any published work. We propose a novel approach to solving both problems in the same framework. Particularly it preserves the effects relation of concurrent operations so that convergence is achieved automatically. Our work provides a new perspective into group editors and operational transformation algorithms.

Real-time group editors allow distributed users to work on local replicas of a shared document simultaneously to achieve high responsiveness and free interaction. Operational transformation (OT) is the standard method for consistency maintenance in state-of-the-art group editors. It is potentially able to achieve content consistency (convergence) as well as intention consistency (so that the converged content is what the users intend), while traditional concurrency control methods such as locking and serialization often cannot. However, existing OT algorithms are often not able to really guarantee consistency due to important algorithmic flaws that have been there for fourteen years. We present a novel state difference based transformation (SDT) algorithm to solve the problem. Our result also reveals that the standard priority schemes to break ties in distributed systems should be used with more caution.

Multi-user applications generally lag behind in features or compatibility with single-user applications. As a result, users are often not motivated to abandon their favorite single-user applications for groupware features that are less frequently used. A well-accepted approach, collaboration transparency, is able to convert off-the-shelf single-user applications into groupware without modifying the source code. However, existing systems have been largely striving to develop generic application-sharing mechanisms and undesirably force users to share the same application in cooperative work. In this paper we analyze this problem and present a novel approach (called intelligent collaboration transparency) to addressing this problem. Our approach allows for heterogeneous application sharing by considering the particular semantics of the applications and the collaboration task in question.