Of course, these wonderful applications depend not only on grid power, but also on data, and often on vast volumes of heterogeneous, distributed data, collected or generated by various groups, and stored in diverse systems. The data sources might be files, databases, or applications. For the promise of grid to be fulfilled, not only must we harness and visualizer multiple computing resources, but we must also abstract and hide the diversity and distribution of these various information sources to provide applications with a single, powerful virtual information store for their virtual computer.