The second and third authors are currently completing their dissertations
under the supervision of the first author. Our research along the lines
discussed in this paper, including development of the multi-interface
POLYGLOT architecture and environment by the first and second authors,
and of the multi-modal POLYMESTRA architecture and environment by
the first and third authors, has been supported, in part, by the National
Science Foundation under contracts IRI-9213823 and CCR-9527151.