HUMAN-COMPUTER INTERACTION SECOND EDITION
Dix, Finlay, Abowd and Beale

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Chapter 13 Groupware 13.7.5 Graphical toolkits Page 501

More fundamentally, the functionality of toolkit widgets may be insufficient for groupware. This is particularly obvious for text areas. The toolkit often takes over a lot of the tedium of handling an editable text region: the user can type and delete, do cursor movement and even cut and paste, all without the application's intervention. However, the groupware developer may want to have multiple cursors, or to ensure that all the participants can see the same portion of a document. Unfortunately, even information such as what portion of the document is in view, or where a particular logical character is displayed on the screen is difficult to come by, as is control over a scrollbar if this is to be shared. One is often forced to design the application round the limited capabilities of the text widget, or to use bitmap operations to paint the text oneself.

Chapter 13 Groupware 13.7.5 Graphical toolkits Page 501

Despite the difficulties of toolkits, some have facilities which are a positive help. For example, the SunView toolkit and its X version, XView, are both notification based (see Chapter 10). As well as notifications of user events, they can be asked to tell you when a network channel is ready for reading or writing. Thus, the interface and the network can be programmed in a similar style.

Chapter 13 Groupware Workstation faults Page 503

More often, individual workstations, or the programs running on them, will crash. This is partly because there are more of them, and partly because their code is more complex. In particular, these programs are handling all the user's interactions and are built upon complex (and frequently flaky) graphical toolkits. Of course, one tries to program carefully and avoid these errors, but experience shows that they will continue to occur. The aim is to confine the fault to the particular user concerned and to recover from the fault as quickly as possible. When thinking about a client--server architecture, there are three 'R's for the server:

Chapter 13 Groupware 13.8 Summary Page 507

Groupware systems are more complex than single-user ones. We considered architectures for synchronous groupware, client--server and replicated, and for shared windowed systems. The choice of architecture combined with network delays influences the sort of feedback participants receive of their own actions. As important, it also influences the feedthrough they experience of other participants' actions. The widgets supplied by graphical toolkits are designed with single-user applications in mind, and so the groupware designer must either fit around these limitations or program group widgets from scratch. Finally, it is very important that groupware is robust. Problems are more likely to occur owing to the increased complexity, but are more damaging, because of the large number of people affected.

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