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 three main problems: (1) the notion of context is still ill defined; (2) there is a lack of conceptual models and methods to help drive the design of context-aware applications; and (3) no tools are available to jump-start the development of context-aware applications. In this paper, we address these three 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 contextaware 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 contextaware 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.

ABSTRACT:We propose the CARE properties as a simple way of characterising and assessing aspects of multimodal interaction: the Complementarity, Assignment, Redundancy, and Equivalence that may occur between the interaction techniques available in a multimodal user interface. We provide a formal definition of these properties and use the notion of compatibility to show how the system CARE properties interact with user CARE-like properties in the design of a system. The discussion is illustrated with MATIS, a Multimodal Air Travel Information System.

In order for a smart environment to provide services to its occupants, it must be able to detect its current state or context and determine what actions to take based on the context. We discuss the requirements for dealing with context in a smart environment and present a software infrastructure solution we have designed and implemented to help application designers build intelligent services and applications more easily. We describe the benefits of our infrastructure through applications that we have built.

We describe the Conference Assistant, a prototype mobile, context-aware application that assists conference attendees. We discuss the strong relationship between context-awareness and wearable computing and apply this relationship in the Conference Assistant. The application uses a wide variety of context and enhances user interactions with both the environment and other users. We describe how the application is used and the context-aware architecture on which it is based.

We present a way of analyzing sensed context information formulated to help in the generation, documentation and assessment of the designs of context-aware applications. Starting with a model of sensed context that accounts for the particular characteristics of sensing, we develop a method for expressing requirements for sensed context information in terms of relevant quality attributes plus properties of the sensors that supply the information. We demonstrate on an example how this approach permits the systematic exploration of the design space of context sensing along dimensions pertinent to software development. Returning to our model of sensed context, we examine how it can be supported by a modular software architecture for context sensing that promotes separation between context sensing, user interaction, and application concerns.