Computing devices and applications are now used beyond the desktop, in diverse environments, and this trend toward ubiquitous computing is accelerating. One challenge that remains in this emerging research field is the ability to enhance the behavior of any application by informing it of the context of its use. By context, we refer to any information that characterizes a situation related to the interaction between humans, applications, and the surrounding environment. Context-aware applications promise richer and easier interaction, but the current state of research in this field is still far removed from that vision. This is due to 3 main problems: (a) the notion of context is still ill defined, (b) there is a lack of conceptual models and methods to help drive the design of context-aware applications, and (c) no tools are available to jump-start the development of context-aware applications. In this anchor article, we address these 3 problems in turn. We first define context, identify categories of contextual information, and characterize context-aware application behavior. Though the full impact of context-aware computing requires understanding very subtle and high-level notions of context, we are focusing our efforts on the pieces of context that can be inferred automatically from sensors in a physical environment. We then present a conceptual framework that separates the acquisition and representation of context from the delivery and reaction to context by a context-aware application. We have built a toolkit, the Context Toolkit, that instantiates this conceptual framework and supports the rapid development of a rich space of context-aware applications. We illustrate the usefulness of the conceptual framework by describing a number of context-aware applications that have been prototyped using the Context Toolkit. We also demonstrate how such a framework can support the investigation of important research challenges in the area of context-aware computing.

Context-enabled applications are just emerging and promise richer interaction by taking environmental context into account. However, they are difficult to build due to their distributed nature and the use of unconventional sensors. The concepts of toolkits and widget libraries in graphical user interfaces has been tremendously successtil, allowing programmers to leverage off existing building blocks to build interactive systems more easily. We introduce the concept of context widgets that mediate between the environment and the application in the same way graphical widgets mediate between the user and the application. We illustrate the concept of context widgets with the beginnings of a widget library we have developed for sensing presence, identity and activity of people and things. We assess the success of our approach with two example context-enabled applications we have built and an existing application to which we have added context-sensing capabilities.

Claims are being made that videophone facilities on microcomputers allow transparent and effective use of shared work spaces by geographically separated colleagues. This can only be true if the video image helps the users understand each other's everyday speech. This study examines factors affecting the comprehension of deictic, gestural reference in videophone communication. Three camera positions were compared: the standard, 'face-to-face' view of the colleague, a 'reversed' view, and a rear three-quarters 'hind' view. Task conditions involved low referential ambiguity (where reference was verbally explicit as well as deictically indicated by gesture) and high referential ambiguity (deictic reference alone). The reference was either to an item in the workspace or a spatial relationship, and twodimensional and three-dimensional workspaces were compared. Results indicate that the standard face-to-face view found on many systems does not allow gestures made towards shared areas of the screen to be understood when the verbal information is ambiguous. In designing systems that encourage the use of normal patterns of speech, and hence the use of deictic reference, it is necessary to understand which cues are likely to resolve ambiguities, in which dimensions, and the extent to which the cues provided are likely to achieve that end.