We introduce XML (eXtensible Markup Language) as a simple, flexible, and powerful way for computers to exchange metadata and control information, not only with humans, but also with each other. We describe an existing system that delivers customized remote-sensing data products to web-connected clients, and what more is required to support supervised, on-demand processing of the data. We discuss how such an architecture can be used for these purposes, and how it may interoperate with existing parallel SAR processing architectures, or with a GIS application server. Applications of such a system include agriculture, ecology, geophysics, glaciology and hazard-monitoring. (C) 1999 Elsevier Science B.V. All rights reserved.