than physical fidelity.” The Steamer graphical editor became the basis for the HITS system, which was expanded to include additional editors to support multimodal interfaces (graphical, natural language, gestural, and sketch-based) for what we termed high-functionality systems. HITS was built on an underlying knowledge base and provided a run-time environment to support multimodal interaction.

One deep idea in HITS was the
notion of creating a “tool chain”
to permit dynamic changes to be
made at multiple levels. This was
enabled by an integrated repre-
sentation of the interface and, in
fact, of the editors themselves, that
allowed modifications from low-lev-
el details to high-level, task-specific
characteristics. This multilevel
software development environment
was designed to encourage inter-
face evolution and integration of
multiple modalities. We thought it
was a fundamentally flawed notion
that interface design had to be
accomplished either at a low level
by skilled programmers or via high-
level tool kits that, while requiring
less programming expertise, highly
constrained the range of what could
be designed. We were convinced
that to fully exploit the expertise of
designers and encourage evolution
of an interface over time required a
tool chain that connected and inte-
grated the multiple levels of design
necessary to span the enormous
distance between the low-level bit-
shuffling of machines and the com-
plex situated tasks of users.