this article, we examine today's ubiquitous systems, focusing on software infrastructure, and discuss the road that lies ahead

rwise similar cells. Columns correspond to the cells treated by different drug candidates, and rows correspond to gene activity expressed in the form of molecular concentrations. The darkness of the band at each row--column intersection indicates a specific gene's activity level under the drug candidate's influence. A technique called gel electrophoresis, in which researchers use an electric field to sort molecules by size, produces the readout. When genes produce different -sized RNA molecules, this technique can help discriminate between them. In the common biochemical procedure called polymerase chain reaction (PCR), genetic material (RNA, in this case) is amplified (repeatedly duplicated) so we can detect the molecules' presence by using the electrophoresis technique. Thus, the entire experiment consists of . Exposing cells to drug candidates . Destroying the cells and performing PCR on their molecular components . Applying electrophoresis . Taking an image of the gel to captu

This paper presents a general-purpose infrastructure for building and managing location-aware applications in ubiquitous computing settings. The goal of the infrastructure is to provide people, places, and objects with computational functionalities to support and annotate them. Using location-tracking systems the infrastructure can navigate Java-based mobile agents to stationary or mobile computers near the entities and places to which the agents are attached, even when the locations change. The infrastructure enables application-specific functionalities to be implemented within mobile agents instead of the infrastructure itself. It maintains the locations of people and objects, including computing devices, and allows mobile users to directly access their personalized services from stationary computing devices in the environment or from their portable computing devices. This paper presents the rationale, design, implementation, and applications for our prototype infrastructure.

The design constraints in ubiquitous computing (ubicomp) differ from those traditionally emphasized by the systems community: evolvability, long-term maintainability, and robustness to transient failures are essential, while scalability and performance are lesser concerns, due to the nature of ubicomp itself and the performance of today's commodity equipment. We show how these observations are reflected in the design of iROS, a ubicomp software framework in production use. In particular, we show that a centralized architecture directly enables the ubicomp programming abstractions needed while providing the best solution for evolvability and maintainability/deployability, and that we can achieve the required robustness through a fast-recovery strategy, which allows a simple centralized implementation of the architecture. Throughout, we achieve performance, scalability, and recovery behavior sufficient for typical operation.

A user-driven system, although technologically conservative, embraces a central goal of ubiquitous computing: to enhance the ability to perform domain tasks through fluid interaction with computational resources. Smart environments could soon replace the pen and paper commonly used in the laboratory setting.