1) They started with AVS and realized soon that this is not sufficient
for their enormous datasets.
2) Next, they developed something called Tioga which had some VRish elements
and allowed to navigate though n-dimensional datasets by defining
suitable subspaces, cuts etc. It was dataflow as AVS but modules were
more robust and finer grain. In particular, they provided dataflow
interface to Postgres procedures, i.e. support for 'database navigation'.
(Postgres is public precursor of Ingres from UCB and part of Sequoia 2000).
They used Postgres coupled with GRASS (Army/public GIS system).
I'm not sure if Tioga was finished/released.
Tioga papers were on Berkeley ftp.
3) At Supercomputing'93, I have seen a VRish demo by someone related to
Sequoia. It was running on Kubota, using CyberGlove and shutter glasses.
Demo allowed to navigate though a 3D vector field with elements marked
as arrows. Graphics was rather simple. I'm not sure if this was Tioga
demo. My impression was that this was a simple hack, without any fancies
in the backend.
4) Apparently, they made some progress since this time as per WEBster
entry and your pointer. Big River sounds to me as a Tioga follow-on
(btw, Tioga is a name of Yosemite valley or passage).
AVL and IVS must be newer/recently developed systems.