Ubiquitous Computing advocates the construction of massively distributed systems that help transform physical spaces into computationally active and intelligent environments. The design of systems and applications in these environments needs to take account of heterogeneous devices, mobile users and rapidly changing contexts. Most importantly, agents in ubiquitous and mobile environments need to be context-aware so that they can adapt themselves to different situations. In this paper, we argue that ubiquitous computing environments must provide middleware support for context-awareness. We also propose a middleware that facilitates the development of context-aware agents. The middleware allows agents to acquire contextual information easily, reason about it using different logics and then adapt themselves to changing contexts. Another key issue in these environments is allowing autonomous, heterogeneous agents to have a common semantic understanding of contextual information. Our middleware tackles this problem by using ontologies to define different types of contextual information. This middleware is part of Gaia, our infrastructure for enabling Smart Spaces.
