Flexible support for synchronous collaboration with selective window sharing and stateful group communication services.

The ability to share synchronized views of interactions with an application is critical to supporting synchronous collaboration. This thesis presents a flexible synchronous collaboration paradigm, called selective window sharing, in which the sharing of user/application interactions occurs at the window level within a multi-user, multi-window application. Selective window sharing facilitates on-demand sharing of application state and allows private workspace within a shared application. The paradigm is incorporated into a toolkit for building synchronous collaborative applications, called DistView. DistView defines an object-oriented application model that adapts the well-known Model-View-Controller (MVC) programming paradigm. In order to provide low response times for shared windows, DistView uses a selective, object-level replication scheme that allows the widgets and data objects associated with shared windows to be dynamically exported and imported. Providing low response times is critical in supporting the fluid interactions among participants in interactive collaborative environments, especially over a wide area network. Replicating shared windows also increases flexibility in screen real-estate management; for example, users can place, move, and/or iconize shared windows independently of their co-workers. The DistView toolkit works in conjunction with Corona, a communication subsystem that provides stateful group communication services for DistView-based applications. Corona's services are stateful in that Corona can manage shared application objects. Corona's shared object management is message-based and independent of application semantics. Corona also provides state synchronization and group membership notification services, to which clients can selectively subscribe. The initial versions of DistView and Corona are implemented in Java and have been successfully tested and used for supporting team science over a wide-area network in the Upper Atmospheric Research Collaboratory (UARC) project. This thesis provides a detailed discussion of the design of DistView and Corona and describes its usage in the UARC project.Ph.D.Applied SciencesComputer scienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131787/2/9929952.pd

DistView: support for building efficient collaborative applications using replicated objects

The ability to share synchronized views of interactions with an application is critical to supporting synchronous collaboration. This paper suggests a simple synchronous collaboration paradigm in which the sharing of the views of user/application interactions occurs at the window level within a multi-user, multi-window application. The paradigm is incorporated in a toolkit, DistView, that allows some of the application windows to be shared at a fine-level of granularity, while still allowing other application windows to be private. The toolkit is intended for supporting synchronous collaboration over wide-area networks. To keep bandwidth requirements and interactive response time low in such networks, DistView uses an object-level replication scheme, in which the application and interface objects that need to be shared among users are replicated. We discuss the design of DistVlew and present our preliminary experience with a prototype version of the system

Tolerating Client and Communication Failures in Distributed Groupware Systems

If a groupware system is to be effectively used, especially over a wide-are network such as the Internet, where the quality of networking and computing resources are unpredictable, it should allow clients to tolerate client, link, and server failures. In particular, clients should be able to join groups and transfer groups' current state in the presence of most client and link failures. In order to reduce usage overhead, disconnected clients should also be able to rejoin groups without having to restart from scratch. Furthermore, lock management and group membership should tolerate transient failures in the system. In this paper, we introduce the notion of stateful group communication, which frees clients of administrative management of shared application state and allows fault-tolerant group join, state transfer, and rejoin. Stateful group communication is incorporated in Corona, a general-purpose, group communication service provider. In order to allow groups to tolerate transient failures, Corona also provides locks with grace period and group membership notification services that are based on client connection status. In this paper, we present and discuss Corona's fault-tolerant services

Providing Flexible Services for Managing Shared State in Collaborative Systems

To effectively collaborate in Internet environments, it is critical to efficiently manage the shared state of collaboration. However, the management of shared state is highly situational; different collaboration semantics require different measures tailored to their specific needs. Hence, providing a general set of services that meet the management requirements of varying collaboration situations is challenging. In this paper, we discuss our approach to providing such services. The services are made flexible by allowing collaborators to choose appropriate services based on the needs of their collaboration tools and specific characteristics of their shared state. We present the shared state management services provided by our Corona server that embodies our approach and report experience with its use

Data Management Issues and Trade-Offs in CSCW Systems

Substantial interest has developed in recent years in building computer systems that support cooperative work among groups without the need for physical proximity. This paper examines some of the difficult data management issues in designing systems for computer-supported cooperative work (CSCW). Specifically, we consider an example CSCW system to support large-scale team science over the Internet, Collaboratory Builder's Environment; we discuss the issues of managing shared data in such systems, reducing information overload, and providing group awareness and access control. We discuss several promising approaches to these issues. We point out where a significant gap remains in addressing the requirements of such systems and where designers have to make design trade-offs that can be difficult to evaluate. Finally, we discuss several open issues for future work