Synchronous groupware depends on the assumption that people are fully connected to the others in the group, but there are many situations (network delay, network outage, or explicit departure) where users are disconnected for various periods. There is little research dealing with disconnection in synchronous groupware from a user and application perspective; as a result, most current groupware systems do not handle disconnection events well, and several user-level problems occur. To address this limitation, we developed the Disco framework, a model for handling several types of disconnection in synchronous groupware. The framework considers how disconnections are identified, what senders and receivers should do during an absence, and what should be done with accumulated data upon reconnection. We have implemented the framework in three applications that show the feasibility, generality, and functionality of our ideas. Our framework is the first to deal with a full range of disconnection issues for synchronous groupware, and shows how groupware can better support the realities of distributed collaboration.

This paper identifies a set of distribution architectures for the development of synchronous groupware and provides an analysis of their quality attributes. The architectures and their quality attributes provide insight on how to structure the implementation of synchronous groupware applications, providing developers with precise guidance on the trade-offs between various implementation techniques. In contrast to many proposed architectures for groupware, these architectures have been synthesized through analysis of successful groupware systems whose properties are well-understood

This paper presents visual constraint diagrams (VCD), an extension to UML (Unified Modeling Language) object diagrams for expressing constraints over object models. VCD allows designers to express well-formedness constraints that cannot be expressed using class diagrams alone; an example of such a constraint is that a linked list data structure cannot have any loops. VCD offers two advances over existing techniques: (1) they allow constraints to be expressed within the visual notation of UML, without resorting to complex textual notations such as OCL; and (2) VCD can be checked at runtime, increasing the value of design documents to developers. An editor and a checker for VCD have been implemented as part of the Rosetta software design tool.