Many of the ideas in this paper have been developed and elaborated in collaboration with Stephanie Forrest; but for exigencies of time and deadlines she would have been a co-author. The ccr development group at UNM has included Adam Messinger, Brian Clark, Neal Fachan, Nathan Wallwork, Suresh Madhu, Peter Neuss, Steve Coltrin, and Jeff Moser. This work was supported in part by an NSF research infrastructure grant, award number CDA-95-03064, and in part by the DARPA Intelligent Collaboration and Visualization program, contract number N66001-96-C-8509.