The UNC Collaboratory project is concerned with both the process of collaboration and with computer systems to support that process. Here, we describe a component of the Artifact-Based Collaboration (ABC) system, called the Matrix, that provides an infrastructure in which existing single-user applications can be incorporated with few, if any, changes and used collaboratively. We take the position that what is needed is not new tools but better infrastructure for using familiar single-user tools collectively. The paper discusses the Matrix architecture, a Virtual Screen component, and generic functions that provide conferencing, hyperlinking, and recording of users' actions for all applications.

Shared window systems have become a popular vehicle for supporting distributed, synchronous collaboration. A t present they are diflcult to build and they support limited paradigms of multi-user interaction with shared applications. We believe this dificulty as largely due to the inverted nature of the client/server architecture of most distributed window systems. The architecture is inverted in the sense that the user is nearer the server than the client; this hampers attempts to share windows. By comparing the traditional client/server architecture of distributed j l e systems with the inverted architecture of distributed window systems we argue that it is possible to develop window systems where the user is nearer window system clients than servers, and that this architecture greatly facilitates the sharing of windows among users.

A large number of experimental (and a few commercial) distributed synchronous collaboration support systems have been developed to date for the UNIX 4 /X environment. These systems typically fall into one of two categories: toolkits for collaborative application development, and shared window systems. Collaboration toolkits usually focus on supporting the development of collaboration-aware applications, and shared window systems are typically in tended to make existing single-user (collaboration-unaware) applications available to multiple users concurrently. The two types of systems are usually developed and used independently; that is, integrated systems with the capabilities of both types of systems are rare.This field of research is now mature enough that we can identify the major components of such systems and the functions they typically provide. In this paper we analyze a typical partitioning of function among the usual set of components, and suggest changes that can be made to this partitioning to improve the characteristics of future collaborative support systems. In the process, we find that our re-distribution of function makes it easier to develop integrated systems supporting both collaboration-aware and collaboration-unaware applications.