We have developed a new model for coupling the user interfaces of a multiuser program. It is based on an interaction model and a user interface framework that allow users and programmers, respectively, to view applications as editors of data. It consists of a semantics model, a specification model, and an implementation model for coupling. The semantics model determines (1) which properties of interaction entities created for a user are shared with corresponding interaction entities created for other users and (2) when changes made by a user to a property of an interaction entity are communicated to other users sharing it. It divides the properties of an interaction entity into multiple coupling sets and allows users to share different coupling sets independently. It supports several criteria for choosing when a change made by a user to a shared property is communicated to other users. These criteria include how structurally complete the change is, how correct it is, and the time at which it was made. The specification model determines how users specify the desired semantics of coupling. It associates interaction entities with inheritable coupling attributes, allows multiple users to specify values of these attributes, and does a runtime matching of the coupling attributes specified by different users to derive the coupling among their user interfaces. The implementation model determines how multiuser programs implement user-customizable coupling. It divides the task of implementing the coupling between system-provided modules and application programs. The modules support automatically a predefine semantics and specification model that can be extended by the programs. We have implemented the coupling model as part of a system called Suite. This paper describes and motivates the model using the concrete example of Suite, discusses how aspects of it can be implemented in other systems, compares it with related work, discusses its shortcomings, and suggests directions for future work.

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We have developed a high-level and flexible framework for supporting the construction of multiuser interfaces. The framework is based on a generalized editing interaction model, which allows users to view programs as active data that can be concurrently edited by multiple users. It consists of several novel components including a refinement of both the Seeheim UIMS architecture and the distributed graphics architecture that explicitly addresses multiuser interaction; the abstractions of shared active variables and interaction variables, which allow users and applications to exchange information; a set of default collaboration rules designed to keep the collaboration-awareness low in multiuser programs; and a small but powerful set of primitives for overriding these rules. The framework allows users to be dynamically added and removed from a multiuser sesssion, different users to use different user interfaces to interact with an application, the modules interacting with a particular user to execute on the local workstation, and programmers to incrementally trade automation for flexibility. We have implemented the framework as part of a system called Suite . This paper motivates, describes, and illustrates the framework using the concrete example of Suite, discusses how it can be implemented in other kinds of systems, compares it with related work, discusses its shortcomings, and suggests directions for future work.

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We have designed a set of primitives for programming multi-user interfaces by extending a set of existing highlevel primitives for programming single-user interfaces.These primitives support both collaboration-transparent and collaboration-aware multi-user programs and allow existing single-user programs to be incrementally changed to corresponding multi-user programs, The collaborationaware primitives include primitives for tailoring the input and output to a user, authenticating users, executing code in a user's environment and querying and setting properties of it, and tailoring the user interface coupling.We have identified several application-independent user groups that arise in a collaborative setting and allow the original single-user calls to be targeted at these groups. In addition, we provide primitives for defining application-specific groups. Our preliminary experience with these primitives shows that they can be used to easily implement collaborative tasks of a wide range of applications including message systems, multi-user editors, computer conferencing systems, and coordination systems.In this paper, we motivate, describe, and illustrate these primitives, discuss how primitives similar to them can be offered by a variety of user interface tools, and point out future directions for work.