An application like Cyberguide can take advantage of user mobility by adapting behavior based on knowledge of the user's current location. This location can refer to the position and orientation of a single person, many people, or even of the application itself. Location is a simple example of context, that is, information about the environment associated with an application. Context-aware computing involves application development that allows for collection of context and dynamic program behavior dictated by knowledge of this environment. Researchers are increasing our ability to sense the environment and to process speech and video and turn those signals into information that expresses some understanding of a real-life situation. In addition to dealing with raw context information such as position, a context-aware application is able to assign meaning to the events in the outside world and use that information effectively.
Context-awareness is not unique to ubiquitous computing. For example, explicit user models used to predict the level of user expertise or mechanisms to provide context-sensitive help are good examples used in many desktop systems. With increased user mobility, and with increased sensing and signal processing capabilities, there is a wider variety of context available to tailor program behavior. Moreover, context-awareness is a critical feature for a ubiquitous computing system because important context changes are more frequent. In a ubiquitous computing environment it is likely that the physical interfaces will not be ``owned'' by any one user. When a user owns the interface --as is usually the case with personal digital assistant or a laptop computer-- over time this interface can be personalized to the user. Context can be useful in these situations, as has been demonstrated by location-aware computing applications. When the user does not own the interface, it is likely that the same physical interface will be used by many people. Any single user (or group of users) will prefer to have the interface personalized for the duration of the interaction. Context-awareness will allow for this rapid personalization of computing services.
The restricted context-awareness based on position was the focus of Cyberguide and many other research efforts have focussed on location-aware computing [25, 21, 26, 22]. In Classroom 2000, a different kind of context was necessary. We used information about the location of the electronic whiteboard and the schedule of classes to automatically predict what class was beginning and drastically streamline start-up activities. It was also important to determine focus of class discussion (Web page or electronic whiteboard slide) in order to decorate the timeline of the captured notes (shown in Figure 2) with the relevant item. In variations of the Zen* system that we have built to support informal and unscheduled meetings, we use a number of different sensing techniques to determine when a recorded session should begin and who is in attendance, all of which is contextual information.