Browsing by Author "Li, Du"
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- Journal ArticleAn Admissibility-Based Operational Transformation Framework for Collaborative Editing Systems(Computer Supported Cooperative Work (CSCW): Vol. 19, No. 1, 40210) Li, Du; Li, RuiOperational transformation (OT) as a consistency control method has been well accepted in group editors. With OT, the users can edit any part of a shared document at any time and local responsiveness is not sensitive to communication latencies. However, established theoretical frameworks for developing OT algorithms either require transformation functions to work in all possible cases, which complicates the design of transformation functions, or include an under-formalized condition of intention preservation, which results in algorithms that cannot be formally proved and must be fixed over time to address newly discovered counterexamples. To address those limitations, this paper proposes an alternative framework, called admissibility-based transformation (ABT), that is theoretically based on formalized, provable correctness criteria and practically no longer requires transformation functions to work under all conditions. Compared to previous approaches, ABT simplifies the design and proofs of OT algorithms.
- Journal ArticleAn Approach to Ensuring Consistency in Peer-to-Peer Real-Time Group Editors(Computer Supported Cooperative Work (CSCW): Vol. 17, 2008) Li, Du; Li, RuiReal-time group editors allow distributed users to edit a shared document at the same time over a computer network. Operational transformation (OT) is a well accepted consistency control method in state-of-the-art group editors. Significant progress has been made in this field but there are still many open issues and research opportunities. In particular, established theoretic OT frameworks all require that OT algorithms be able to converge along arbitrary transformation paths. This property is desirable because group editors that implement such algorithms will not rely on a central component for achieving convergence. However, this has not been achieved in any published work to our knowledge. We analyze the root of this problem and propose a novel state difference based transformation (SDT) approach which ensures convergence in the presence of arbitrary transformation paths. Our approach is based on a novel consistency model that is more explicitly formulated than previously established models for proving correctness. SDT is the first and the only OT algorithm proved to converge in peer-to-peer group editors.
- Journal ArticleAn Operational Transformation Algorithm and Performance Evaluation(Computer Supported Cooperative Work (CSCW): Vol. 17, 39783) Li, Du; Li, RuiOperational transformation (OT) is an optimistic concurrency control method that has been well established in realtime group editors and has drawn significant research attention in the past decade. It is generally believed that the use of OT automatically achieves high local responsiveness in group editors. However, no performance study has been reported previously on OT algorithms to the best of our knowledge. This paper extends a recent OT algorithm and studies its performance. By theoretical analyses and performance experiments, this paper proves that the worst-case execution time of OT only appears in rare cases, and shows that local responsiveness of OT-based group editors in fact depends on a number of factors such as the size of the operation log. The paper also reveals that these two results have general implications on OT algorithms and hence the design of OT-based group editors must pay attention to performance issues.
- Text DocumentDemonstrational Customization of a Shared Whiteboard to Support User-Defined Semantic Relationships among Objects(Proceedings of the 2001 ACM International Conference on Supporting Group Work, 2001) Li, Du; Patrao, JasonAs a promising approach to end-user computing, programming by demonstration (PBD) techniques have been explored by many researchers in single-user applications. This paper investigates how PBD techniques can be used to support end-user customization of groupware tools. In collaborative applications, complex semantic relationships can emerge unanticipatedly among objects (participants, data artifacts, tools, devices, etc.) such as the hierarchical organization of participants, consistency maintenance among different views of the same data, and awareness control. It is important that end users are empowered to customize the groupware application to model and enforce such relationships. We present an active rule based approach to modeling user-defined semantic relationships in collaborative applications and explore a demonstrational approach for end-user customization of collaboration tools to support the definition of those relationships. The presented work is based on our work on a shared whiteboard tool, CAB or Collaborative Active whiteBoard. Our approach is being generalized to support end user defined object relationships in shared workspaces.
- Text DocumentA Landmark-Based Transformation Approach to Concurrency Control in Group Editors(Proceedings of the 2005 ACM International Conference on Supporting Group Work, 2005) Li, Rui; Li, DuOperational 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.