The growth of the Internet and the availability of powerful computers and hi- speed networks as low-cost commodity components are changing the way we do computing. These new technologies have enabled the clustering of a wide variety of geographically distributed resources, such as supercomputers, storage systems, data sources, and special devices and services, which can then be used as a uni?ed resource. Furthermore, they have enabled seamless access to and interaction among these distributed resources, services, applications, and data. The new paradigm that has evolved is popularly termed...