The first users of a new technology are often engineers and enthusiasts. The functionality and interface that they find acceptable may be very different than the requirements of a more mainstream audience. This poses challenges for usability engineers in both defining user groups and then evaluating a product against usability goals, when both users and goals are changing as the technology matures. Usability evaluation methods for collaborative applications must evolve and iterate at least as fast as the products themselves. This paper describes the changes in approach taken by usability engineers between Version 1 and Version 3 of the Microsoft NetMeeting product.

While a large fraction of application code is devoted to graphical user interface (GUI) functions, support for reuse in this domain has largely been confined to the creation of GUI toolkits ("widgets"). We present a novel architectural style directed at supporting larger grain reuse and flexible system composition. Moreover, the style supports design of distributed, concurrent applications. Asynchronous notification messages and asynchronous request messages are the sole basis for intercomponent communication. A key aspect of the style is that components are not built with any dependencies on what typically would be considered lower-level components, such as user interface toolkits. Indeed, all components are oblivious to the existence of any components to which notification messages are sent. While our focus has been on applications involving graphical user interfaces, the style has the potential for broader applicability. Several trial applications using the style are described.