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C00002 00002	∂09-Jan-81  1503	BRoberts at BBNG (Bruce Roberts) 	Abstract for Computer Fair
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∂09-Jan-81  1503	BRoberts at BBNG (Bruce Roberts) 	Abstract for Computer Fair
Date:  9 Jan 1981 1802-EST
From: BRoberts at BBNG (Bruce Roberts)
Subject: Abstract for Computer Fair
To: jra at SU-AI
cc: stevens at BBNG, BRoberts at BBNG

As part of the STEAMER project, we have built a color graphics
interface to a large mathematical model of a ship's steam plant.  With
it, one can watch any of several dynamic views of steam plant
operation and control the steam plant by adjusting valves and flipping
switches on the screen.  The entire system is written in Maclisp and
runs on a Decsystem-20 with an AED 512 color graphics processor for
output and an Elographics touch panel for input.

A schematic view of the steam plant or one of its subsystems is
constructed out of a library of "icons", graphical objects that
contain all information necessary to draw and manipulate the object.
There are icons for various kinds of pumps, turbines, pipes, valves,
gages, motors, and other paraphernalia that compose a steam plant.
The multiplicity of objects, related in their functional
characteristics but differing in details of representation, was
brought under control by organizing them in a class hierarchy.  By
thus compartmentalizing the knowledge about graphical objects, we find
that new objects are easy to add, that it is easy to substitute
different objects in a scene without disrupting the overall layout,
and that we have reduced to a minimum the amount of knowledge other
parts of the system need to have about the particulars of the
graphical interface in order to communicate through it.

Icons vary not only in their appearance, but in how they indicate
state.  Many components of a steam plant are just "on" or "off"; an
icon might depict this by blinking, by its choice of color, or by the
position of some indicator within it.  Continuous variables in the
steam plant simulation can be shown as the level of a column, the
needle on a dial, the value of a digital readout, or the blink rate of
an object.  

An icon can be used for input by supplying it with a method to
interpret a touch at some point within its boundaries.  A simple
on/off icon might return the state opposite what it is currently
indicating; an continuous icon indicator can return the value it would
show at the point being touched.

The communication between the math model and the display is mediated
by another class of computational object we are calling "taps".  Taps
map from variables to an icon and back.  They are necessary because
there is not a one-to-one relationship between the abstract entities
computed in the model and their visual counterparts.  For example, the
notion of a component being "on" may be a complex function of many
variables in the simulation.  Taps translate between the language of
the simulation (in this case, the values of particular Lisp atoms) and
the language of the display icons.

We will show a video tape of an interaction with the STEAMER system,
and of a graphics editor helping to construct schematic views of steam
plants.  We will discuss the organization of our object-based display
system and the extreme advantages of adopting the object-oriented
paradigm for graphic systems, advantages multiplied by imbedding it in
a superior interactive language.  We will touch on our plans to
develop STEAMER into an intelligent tutor in complex thermodynamic
systems.
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