A Web-Based Collaborative Multimedia Presentation Document System

With the distributed and rapidly increasing volume of data and expeditious development of modern web browsers, web browsers have become a possible legitimate vehicle for remote interactive multimedia presentation and collaboration, especially for geographically dispersed teams. To our knowledge, although there are a large number of applications developed for these purposes, there are some drawbacks in prior work including the lack of interactive controls of presentation flows, general-purpose collaboration support on multimedia, and efficient and precise replay of presentations. To fill the research gaps in prior work, in this dissertation, we propose a web-based multimedia collaborative presentation document system, which models a presentation as media resources together with a stream of media events, attached to associated media objects. It represents presentation flows and collaboration actions in events, implements temporal and spatial scheduling on multimedia objects, and supports real-time interactive control of the predefined schedules. As all events are represented by simple messages with an object-prioritized approach, our platform can also support fine-grained precise replay of presentations. Hundreds of kilobytes could be enough to store the events in a collaborative presentation session for accurate replays, compared with hundreds of megabytes in screen recording tools with a pixel-based replay mechanism

Recent advances in petri nets and concurrency

CEUR Workshop Proceeding

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

Developing Collaborative XML Editing Systems

In many areas the eXtensible Mark-up Language (XML) is becoming the standard exchange and data format. More and more applications not only support XML as an exchange format but also use it as their data model or default file format for graphic, text and database (such as spreadsheet) applications. Computer Supported Cooperative Work is an interdisciplinary field of research dealing with group work, cooperation and their supporting information and communication technologies. One part of it is Real-Time Collaborative Editing, which investigates the design of systems which allow several persons to work simultaneously in real-time on the same document, without the risk of inconsistencies. Existing collaborative editing research applications specialize in one or at best, only a small number of document types; for example graphic, text or spreadsheet documents. This research investigates the development of a software framework which allows collaborative editing of any XML document type in real-time. This presents a more versatile solution to the problems of real-time collaborative editing. This research contributes a new software framework model which will assist software engineers in the development of new collaborative XML editing applications. The devised framework is flexible in the sense that it is easily adaptable to different workflow requirements covering concurrency control, awareness mechanisms and optional locking of document parts. Additionally this thesis contributes a new framework integration strategy that enables enhancements of existing single-user editing applications with real-time collaborative editing features without changing their source code

Practical Use of High-level Petri Nets

This booklet contains the proceedings of the Workshop on Practical Use of High-level Petri Nets, June 27, 2000. The workshop is part of the 21st International Conference on Application and Theory of Petri Nets organised by the CPN group at the Department of Computer Science, University of Aarhus, Denmark. The workshop papers are available in electronic form via the web pages: http://www.daimi.au.dk/pn2000/proceeding

A Systematic Approach to Constructing Incremental Topology Control Algorithms Using Graph Transformation

Communication networks form the backbone of our society. Topology control algorithms optimize the topology of such communication networks. Due to the importance of communication networks, a topology control algorithm should guarantee certain required consistency properties (e.g., connectivity of the topology), while achieving desired optimization properties (e.g., a bounded number of neighbors). Real-world topologies are dynamic (e.g., because nodes join, leave, or move within the network), which requires topology control algorithms to operate in an incremental way, i.e., based on the recently introduced modifications of a topology. Visual programming and specification languages are a proven means for specifying the structure as well as consistency and optimization properties of topologies. In this paper, we present a novel methodology, based on a visual graph transformation and graph constraint language, for developing incremental topology control algorithms that are guaranteed to fulfill a set of specified consistency and optimization constraints. More specifically, we model the possible modifications of a topology control algorithm and the environment using graph transformation rules, and we describe consistency and optimization properties using graph constraints. On this basis, we apply and extend a well-known constructive approach to derive refined graph transformation rules that preserve these graph constraints. We apply our methodology to re-engineer an established topology control algorithm, kTC, and evaluate it in a network simulation study to show the practical applicability of our approachComment: This document corresponds to the accepted manuscript of the referenced journal articl

Concurrency Control in Rule-Based Software Development Environments

This dissertation investigates the concurrency control problem in software development environments (SDEs). The problem arises when multiple developers perform activities that concurrently access the project's components, stored as database objects. The interleaved execution of the developers' activities leads to interference if they access overlapping sets of objects concurrently. An SDE can ensure that activities never interfere by modeling their execution in terms of atomic transactions and allowing only serializable schedules. This prevents cooperation, which requires some degree of interference between the activities of multiple developers. To allow cooperation, an SDE must be provided with semantic information about development activities. In rule-based SDEs, the necessary information is readily available in the set of rules that defines the process model of a project. The rules are loaded into the SDE, which provides process-specific assistance through a rule chaining engine. A single user command might lead the chaining engine to initiate a rule chain. The concurrency control problem in rule-based SDEs manifests itself in terms of interference between concurrent rule chains. We present a mechanism that extracts semantic information from the process model to solve the concurrency control problem without obstructing cooperation. The mechanism is composed of two modules: (1) a conflict detection module, which models activities as nested transactions and uses two-phase locking to detect interference; and (2) a conflict resolution module, which employs two protocols to resolve interference. The first protocol, seep, uses the process model to implement a priority-based scheme that aborts the "least important" of the interfering transactions. The second protocol, peep, overrides SCCP by consulting process-specific control rules, written by the project administration. Each control rule describes a specific interference and the actions that resolve it. We have implemented SCCP and parts ofPCCP in MARVEL, a multi-user rule-based SDE developed at Columbia

Concurrency Awareness in a P2P Wiki System

Currently, Wikis are the most popular form of collaborative editors. Recently, some researches have been done to shift from traditional centralized architecture to fully decentralized wikis relying on peer-to-peer networks. This architecture improves scalability and fault-tolerance, but subtly changes the behavior of wiki in case of concurrent changes. While traditional wikis ensure that all wiki pages have been reviewed by, at least, a human, some pages in P2P wiki systems can be the result of an automatic merge done by the system. This forces P2P wiki systems to integrate a concurrency awareness system to notify users about the status of wiki pages. The particular context of a P2P wiki system makes traditional awareness mechanisms inadequate. In this paper, we present a new concurrency awareness mechanism designed for P2P wiki systems