Operation transformation based concurrency control in group editors

Collaborative editing systems (or group editors) allow a geographically dispersed group of human users to view and modify shared multimedia documents, such as research papers, design diagrams, web pages and source code together over a computer network. In addition to being useful tools, group editors are a classic research vehicle and model of interactive groupware applications, based on which a variety of social and technical issues have been investigated. Consistency maintenance as a fundamental problem in group editors has attracted constant research attention. Operational transformation (OT) is an optimistic consistency maintenance method that supports unconstrained collaboration among human users. Although significant progress has been achieved over the past decade, there is still a large space for improvement on the theoretical part of OT. In this dissertation, we are concerned with three problems: (1) How to evaluate the correctness of OT-based consistency maintenance protocols; (2) How to design and prove correct OT-based protocols; (3) What are the consistency correctness conditions for group editing systems in general. This dissertation addresses the above three problems and makes the following contributions: (1) propose a total order based framework including a new consistency model and the associated design methodology. This framework reduces the complexities of the OT design; (2) improve the total order based framework by introducing a natural order based framework. In contrast, this framework removes the requirement of defining a total order that is not necessary to the OT design; (3) establish a generic consistency model and propose the first set of practical design guidelines in OT based on this model

Data Consistency for P2P Collaborative Editing

http://portal.acm.org/Peer-to-peer (P2P) networks are very efficient for distributing content. We want to use this potential to allow not only distribution but collaborative editing of this content. Existing collaborative editing systems are centralised or depend on the number of sites. such systems cannot scale when deployed on P2P networks. In this paper, we propose a new model for building a collaborative editing system. This model is fully decentralised and does not depend on the number of sites

Rethinking Consistency Management in Real-time Collaborative Editing Systems

Networked computer systems offer much to support collaborative editing of shared documents among users. Increasing concurrent access to shared documents by allowing multiple users to contribute to and/or track changes to these shared documents is the goal of real-time collaborative editing systems (RTCES); yet concurrent access is either limited in existing systems that employ exclusive locking or concurrency control algorithms such as operational transformation (OT) may be employed to enable concurrent access. Unfortunately, such OT based schemes are costly with respect to communication and computation. Further, existing systems are often specialized in their functionality and require users to adopt new, unfamiliar software to enable collaboration. This research discusses our work in improving consistency management in RTCES. We have developed a set of deadlock-free multi-granular dynamic locking algorithms and data structures that maximize concurrent access to shared documents while minimizing communication cost. These algorithms provide a high level of service for concurrent access to the shared document and integrate merge-based or OT-based consistency maintenance policies locally among a subset of the users within a subsection of the document – thus reducing the communication costs in maintaining consistency. Additionally, we have developed client-server and P2P implementations of our hierarchical document management algorithms. Simulations results indicate that our approach achieves significant communication and computation cost savings. We have also developed a hierarchical reduction algorithm that can minimize the space required of RTCES, and this algorithm may be pipelined through our document tree. Further, we have developed an architecture that allows for a heterogeneous set of client editing software to connect with a heterogeneous set of server document repositories via Web services. This architecture supports our algorithms and does not require client or server technologies to be modified – thus it is able to accommodate existing, favored editing and repository tools. Finally, we have developed a prototype benchmark system of our architecture that is responsive to users’ actions and minimizes communication costs

The agent architecture InteRRaP : concept and application

One of the basic questions of research in Distributed Artificial Intelligence (DAI) is how agents have to be structured and organized, and what functionalities they need in order to be able to act and to interact in a dynamic environment. To cope with this question is the purpose of models and architectures for autonomous and intelligent agents. In the first part of this report, InteRRaP, an agent architecture for multi-agent systems is presented. The basic idea is to combine the use of patterns of behaviour with planning facilities in order to be able to exploit the advantages both of the reactive, behaviour-based and of the deliberate, plan-based paradigm. Patterns of behaviour allow an agent to react flexibly to changes in its environment. What is considered necessary for the performance of more sophisticated tasks is the ability of devising plans deliberately. A further important feature of the model is that it explicitly represents knowledge and strategies for cooperation. This makes it suitable for describing high-level interaction among autonomous agents. In the second part of the report, the loading-dock domain is presented, which has been the first application the InteRRaP agent model has been tested with. An automated loading-dock is described where the agent society consists of forklifts which have to load and unload trucks in a shared, dynamic environment