The proliferation of wireless networks, hand-held PCs, touch panels, large flat displays, sensors, and embedded devices is transforming traditional habitats and living spaces into ubiquitous computing environments, or active spaces. We envision a middleware software infrastructure that abstracts the heterogeneity of these environments and transforms them into programmable environments. This middleware infrastructure provides support to manage the resources contained in an active space (low-level functionality), support to develop applications (application-level functionality), and support to define interaction rules among applications (active space-level functionality).

In this paper, we present a mechanism called "application bridge" that implements active space-level functionality. Application bridges provide a simple, yet effective, mechanism to define dynamic application composition interaction rules that confer the active space a specific behavior based on a number of parameters, including context, application status, and user actions.