Group Title: Department of Computer and Information Science and Engineering Technical Reports
Title: A Hybrid visual environment for models and objects
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Title: A Hybrid visual environment for models and objects
Series Title: Department of Computer and Information Science and Engineering Technical Reports
Physical Description: Book
Language: English
Creator: Fishwick, Paul A.
Publisher: Department of Computer and Information Science and Engineering, University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: July 13, 1999
Copyright Date: 1999
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Volume ID: VID00001
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A Hybrid Visual Environment for Models and Objects

Paul A. Fishwick

Department of Computer & Information Science & Engineering
University of Florida
Gainesville, Florida 32611, U.S.A.

July 13, 1999


Models and objects that are modeled are usually kept
in different places when we consider most modern
simulation software packages. Software that permits
the user to view 3D objects may also permit a view-
ing of the dynamic models for the objects, but these
views are usually separate. The object can be ro-
tated, translated and navigated while the model is
represented in a 2D fashion using text or 2D iconic
graphics. We present an approached based on the
Virtual Reality Modeling Language (VRML), where
the object and model reside in the same space. A
browsing capability is built to allow the user to search
for models l.III' objects. Aside from the vi-
sual benefits derived from this integrated approach,
this methodology also suggests that models are re-
ally not very different from objects. Any object can
serve to model another object and when these objects
are made I, friendly," it becomes feasible to use
VRML to create distributed models whose compo-
nents can reside anywhere over the web.


One physical object captures some information about
another object. If we think about our plastic toys,
metal trains and even our sophisticated scale-based
engineering models, we see a common thread: to
build one object that says something about another
usually larger and more expensive-object. Let's call
these objects the source object and the target object.
Similar object definitions can be found in the litera-
ture of metaphors (Lakoff 1987) and semiotics (Noth
1990). The source object models the target, and so,
modeling represents a relation between objects. Of-
ten, the source object is termed the model of the tar-
get. We have been discussing scale models identified
by the source and target having roughly proportional
geometries. Scale-based models often suffer from the
problem where changing the scale of a thing affects

more than just the geometry. It also affects the fun-
damental laws applied at each scale. For example,
the hydrodynamics of the scaled ocean model may
be different than for the real ocean. Nevertheless, we
can attempt to adjust for the scaling problems and
proceed to understand the larger universe through a
smaller, more manipulable, version.
Later on in our education, we learned that mod-
eling has other many other forms. The mathematical
model represents variables and symbols that describe
or model an object. Learning may begin with alge-
braic equations such as d -= at2 + vot + do where d,
v and a represent distance, velocity and acceleration,
and where do and vo represent initial conditions (i.e.,
at time zero) for starting distance and initial veloc-
ity. These models are shown to be more elegantly
derived from Newton's laws, yielding ordinary differ-
ential equations of the form f ma. How do these
mathematical, equational models relate to the ones
we first learned as children?
To answer this question, let's first consider what
is being modeled. The equations capture attributes
of an object that is undergoing change in space (i.e.,
distance), velocity and acceleration. However, none
of the geometrical proportions of the target are cap-
tured in the source since the structure of the equa-
tions is invariant to the physical changes in the tar-
get. A ball can change shape during impact with the
ground, but the equations do not change their shape.
If a ball represents the target, where is the source?
The source is the medium in which the equations are
presented. This may, at first, seem odd but it really
is no different than the toy train model versus the
actual train. The paper, phosphor or blackboard
along with the medium for the drawing, excitation
or marking-has to exist if the equations are to ex-
ist. In a Platonic sense, we might like to think of
the equations as existing in a separate, virtual, non-
physical space. While one can argue their virtual
existence, this representation-less and non-physical
form is impractical. Without a physical represen-

station, the equation cannot be communicated from
one human to another. The fundamental purpose of
representation and modeling is communication. Ver-
bal representations (differential air pressure) are as
physical as those involving printing or the exciting of
a phosphor via an electron beam.


Since 1989 at the University of Florida, we have
constructed a number of modeling and simulation
packages documented in (Fishwick 1992; Cubert
and Fishwick 1998) In late 1998, we started de-
signing Rube, named in dedication to Rube Gold-
berg (Marzio 1973), who produced many fanciful car-
toon machines, all of which can be considered mod-
els of behavior. The procedure for creating models
is defined as follows. Step 1: The user begins with
an object that is to be modeled. For JPL, this can
be the Cassini spacecraft with all of its main sys-
tems: propulsion, guidance, science instrumentation,
power, and telecommunication. If the object is part
of a larger scenario, this scenario can be defined as the
top-most root object; Step 2: scene and interactions
are sketched in a story board fashion, as if creating a
movie or animation. A scene is where all objects, in-
cluding those modeling others, are defined within the
VRML file. VRML stands for Virtual Reality Mod-
eling Language (Carey and Bell 1997), which repre-
sents the standard 3D language for the web. The
Rube model browser is made available so that users
can "fly though" an object to view its models with-
out necessarily cluttering the scene with all objects.
However, having some subset of the total set of mod-
els surfaced within a scene is also convenient for aes-
thetic reasons. The modeler may choose to build sev-
eral scenes with models surfaced, or choose to view
objects only through the model browser that hides all
models as fields of VRML object nodes; Step 3: The
shape and structure of all Cassini components are
modeled in any modeling package that has an export
facility to VRML. Most packages, such as Kinetix
3DStudioMax and Autodesk AutoCAD have this ca-
pability. Moreover, packages such as CosmoWorlds
and VRCreator can be used to directly create and
debug VRML content; Step 4: VRML PROTO (i.e.,
prototype) nodes are created for each object and
component. This step allows one to create seman-
tic attachments so that we can define one object to
be a behavioral model of another (using a behav-
ior field) or to say that the Titan probe is part of
the spacecraft (using a contains field), but a sibling
of the orbiter. Without prototypes, the VRML file
structure lacks semantic relations and one relies on

simple grouping nodes, which are not sufficient for
clearly defining how objects relate to one another;
Step 5: Models are created for Cassini. While mul-
tiple types of models exist, we have focused on dy-
namic models of components, and the expression of
these components in 3D. Even textually-based mod-
els that must be visualized as mathematical expres-
sions can be expressed using the VRML text node.
Models are objects in the scene that are no differ-
ent structurally from pieces of Cassini-they have
shape and structure. The only difference is that when
an object is "modeling" another, one interprets the
object's structure in a particular way, using a dy-
namic model template for guidance; Step 6: Sev-
eral dynamic model templates exist. For Newell's
Teapot (in Sec. 3), we used three: FBM, f.. I EQN.
These acronyms are defined as follows: F''. =I Fi-
nite State Machine; FBM Functional Block Model;
EQN Equation Set. Equations can be algebraic,
ordinary differential, or partial differential; Step 7:
The creative modeling act is to choose a dynamic
model template for some behavior for Cassini and
then to pick objects that will convey the meaning
of the template within the scenario. This part is a
highly artistic enterprise since literally any object can
be used. In VRML, one instantiates an object as a
model by defining it: DEF Parthenon-Complex FSM
{...}. In other words, a collection of Parthenon-
type rooms are interconnected in such a way that each
Parthenon-Room maps to a state of the f '-. I Portals
from one room to another become transitions, and
state-to-state transitions become avatar movements
navigating the complex; Step 8: There are three dis-
tinct types of roles played modelers in Rube. At the
lowest level, there is the person creating the model
templates (1'- <'.. IFBM,EQN,PETRI-NET). Each dy-
namic model template reflects an underlying system-
theoretic model (Fishwick 1995). At the mid-level,
the person uses an existing model template to create
a metaphor. A Parthenon-Complex as described be-
fore is an example of an architectural metaphor. At
the highest level, a person is given a set of metaphors
and can choose objects from the web to create a
model. These levels allow modelers to work at the
levels where they are comfortable. Reusability is cre-
ated since one focuses on the level of interest; Step
9: The simulation proceeds by the modeler creating
threads of control that pass events from one VRML
node to another. This can be done in one of two ways:
1) using VRML Routes, or 2) using exposed fields
that are accessed from other nodes. Method 1 is fa-
miliar to VRML authors and also has the advantage
that routes that extend from one model component
to an adjacent component (i.e., from one state to an-
other or from one function to another) have a topolog-

ical counterpart to the way we visualize information
and control flow. The route defines the topology and
data flow semantics for the simulation. Method 2 is
similar to what we find in traditional object-oriented
programming languages where information from one
object is made available to another through an assign-
ment statement that references outside objects and
classes. In method 1, a thread that begins at the root
node proceeds downward through each object that is
role-playing the behavior of another. The routing
thread activates Java or Javascript Script nodes that
are embedded in the structures that act as models or
model components for the behaviors; Step 10: Pre-
and Post-processing is performed on the VRML file
to check it for proper syntax and to aid the modeler.
Pre-processing tools include wrappers (that create a
single VRML file from several), decimators (that re-
duce the polygon count in a VRML file), and VRML
parsers. The model browser mentioned earlier is a
post-production tool, allowing the user to browse all
physical objects to locate objects that model them.
In the near future, we will extend the parser used
by the browser to help semi-automate the building of
script nodes.
Rube treats all models in the same way. For a
clarification of this remark, consider the traditional
use of the word I;..... liI," as used in everyday
terms. A model is something that contains attributes
of a target object, which it is modeling. Whereas,
equation and 2D graph-based models could be viewed
as being fundamentally different from a commonsense
model, Rube views them in exactly the same context:
everything is an object with physical extent and mod-
eling is a relation among objects. This unification is
theoretically pleasing since it unifies what it means
to "model" regardless of model type.


In the early days of computer graphics (c. 1974-75),
Martin Newell rendered a unique set of Bezier surface
spline patches for an ordinary teapot, which currently
resides in the Computer Museum in Boston. The
teapot was modeled by Jim Blinn and then rendered
by Martin Newell and Ed Catmull at the University
of Utah in 1974. While at this late date, the teapot
may seem quaint, it has been used over the years as
an icon of sorts, and more importantly as a bench-
mark for all variety of new techniques in rendering
and modeling in computer graphics. The Teapot was
recently an official emblem of the 25th anniversary
of the AC: I Special Interest Interest Group on Com-
puter Graphics (SIGGRAPH).

One of our goals for Rube was to recognize that
the Teapot could be used to generate another poten-
tial benchmark-one that captured the entire teapot,
its contents and its models. The default teapot has no
behavior and has no contents; it is an elegant piece of
geometry but it requires more if we are to construct
a fully digital teapot that captures a more complete
set of knowledge. In its current state, the teapot is
analogous to a building facade on a Hollywood film
studio backlot; it has the shape but the whole entity
is missing. In VRML, using the methodology previ-
ously defined, we built TeaWorld in Fig. 1. We have
added extra props so that the teapot can be visual-
ized, along with its behavioral model, in a reasonable
contextual setting. The world is rendered in Fig. 1
using a web browser. World is the top-most root of
the scene graph. It contains a Clock, BoilingSystem,
and other objects such as the desk, chairs, floor and
walls. The key fields in Fig. 2 are VRML nodes of the
relevant field so that the contains field is refers to mul-
tiple nodes for its value. This is accomplished using
the VRML MFNode type. The hierarchical VRML
scene graph for Fig. 1 is illustrated in Fig. 2. The

Wo Id

Clock Boiling System Furniture Floor Walls
---4,a~j5 ----

Pipiline Knob Water Thermometer

MYc nel achine2 MMchine3

Tar k1 Tar k3 Pipel ipe3

T nk2 -- - Plpe2 'APlpe4
b 4
Cllck_- Boardl Board3
L - - A
--- ---PBoard2

Figure 2: VRML Scene Graph for the Teapot and its

scene contains walls, a desk, chair and a floor for
context. On the desk to the left is the teapot which
is filled with water. The knob controlling whether
the teapot heating element (not modeled) is on or

Figure 1: Office scene with Newell Teapot, dynamic model and props.

off is located in front of the teapot. To the right of
the teapot, there is a pipeline with three machines,
each of which appears in Fig. 1 as a semi-transparent
cube. Each of these machines reflects the functional
behavior of its encapsulating object: Machinel for
Knob, Machine2 for Water and Machine3 for Ther-
mometer. The Thermometer is a digital one that is
positioned in Machine3, and is initialized to an arbi-
trary ambient temperature of 0 C. Inside Machine2,
we find a more detailed description of the behavior
of the water as it changes its temperature as a re-
sult of the knob turning. The plant inside Machine2
consists of Tankl, Tank2, Tank3, and four pipes that
move information from one tank to the next. Inside
of each tank, we find a blackboard on which is drawn
a differential equation that defines the change in wa-
ter temperature for that particular state. The fol-
lowing modeling relationships are used: Pipeline is a
Functional Block Model (FBM), with three functions
(i.e., machines); Machine is a function (i.e., semi-
transparent cube) within an FBM; Plant is a Finite
State Machine (I1 I) inside of Machine 2; Tank is a
state within a F "'. I and represented by a red sphere;
Pipe is a transition within aF '-,. I and represented by
a green pipe with a conical point denoting direction
of control flow; and Board is a differential equation,
represented as white text. The following metaphors
are defined in this example. The three cubes repre-
sent a sequence of machines that create a pipeline.
One could have easily chosen a factory floor sequence
of numerically controlled machines from the web and
then used this in TeaWorld to capture the informa-

tion flow. Inside the second machine, we find a plant,
not unlike a petroleum plant with tanks and pipes.
The Pipeline and its components represent phys-
ical objects that can be acquired from the web.
For our example, we show simple objects but they
have been given meaningful real-world application-
oriented names to enforce the view that one ob-
ject models another and that we can use the web
for searching and using objects for radically differ-
ent purposes than their proposed original function.
The overriding concern with this exercise is to per-
mit the modeler the freedom to choose any object
to model any behavior. The challenge is to choose a
set of objects that provide metaphors that are mean-
ingful to the modeler. In many cases, it is essen-
tial that more than one individual understand the
metaphorical mappings and so consensus must be
reached during the process. Such consensus occurs
routinely in science and in modeling when new mod-
eling paradigms evolve. The purpose of Rube is not to
dictate one model type over another, but to allow the
modelers freedom in creating their own model types.
In this sense, Rube can be considered a meta-level
modeling methodology.
The simulation of the VRML scene shown in
Fig. 2 proceeds using the dashed line thread that be-
gins with the Clock. The clock has an internal time
sensor that controls the VRML time. The thread cor-
responds closely with the routing structure built for
this model. It starts at Clock and proceeds downward
through all behavioral models. Within each behav-

ioral model, routes exist to match the topology of
the model. Therefore, Machinel sends information
to Machine, which accesses a lower level of abstrac-
tion and sends its output to Machine3, completing
the semantics for the FBM. The '-I. I level contains
routes from each state to its outgoing transitions.
Fig. 3 shows a closeup view of the pipeline, that
represents the dynamics of the water, beginning with
the effect of the turning of the knob and ending with
the thermometer that reads the water temperature.
Figs. 4,5 and 6 show the pipeline during simu-

Figure 6: Cooling state.

Figure 3: Pipeline closeup.

Figure 4: Cold state.

Figure 5: Heating state.

nation when the knob is turned on and off at ran-
dom times by the user. The default state is the cold
state. When the knob is turned to the on position,
the system moves into the heating state. When the
knob is turned again back to an off position, the
system moves into the cooling state and will stay
there until the water reaches ambient room temper-

Figure 7: Outside the Heating phase.

ature at which time the system (through an internal
state transition) returns to the cold state. Temper-
ature change is indicated by the color of Water and
Machine, in addition to the reading on the Ther-
mometer inside of Machine3. The material prop-
erties of Machinel change depending on the state
of the knob. When turned off, Machinel is semi-
transparent. When turned on, it turns opaque. Inside
Machine, the current state of the water is reflected
by the level of intensity of each Plant. The current
state has an increased intensity, resulting in a bright
red sphere.
The dynamics of temperature is indicated at two
levels. At the highest level of the plant, we have a
three state f '.. I Within each state, we have a differ-
ential equation. The equation is based on Newton's
Law of Cooling and results in a first order exponen-
tial decay and rise that responds to the control input
from the knob. The visual display of temperature
change confirms this underlying dynamics since the
user finds the temperature changing ever more slowly
when heating to 100C or cooling back to the ambient
temperature. Fig. 7 displays a closeup of the heat-
ing phase from the outside, and Fig. 8 is a view from
inside the red sphere modeling the phase.
Given the Newell Teapot scene, there are some
key issues which we should ask ourselves: Is it a vi-
sualization? The work in Rube provides visualiza-

Figure 8: Inside the Heating phase.

tion, but models such as Cassini and Newell's Teapot
demonstrate active modeling environments whose ex-
istence serves an engineering purpose and not only
a post-project visualization purpose for outside vis-
itors. This sort of modeling environment is needed
from the very start of a mission-as an integral piece
of the puzzle known as model design; Is it economi-
cal? Is this a lot of work just to create an f '-'. I Why
go through the bother of creating the Parthenon, the
complex and the avatar? All of these items are reused
and so can be easily grabbed from the web. The
concept of reuse is paramount to the Rube approach
where the metaphor can be freely chosen and imple-
mented. Without the web, Rube would not be possi-
ble. 3D object placement can be just as economical
as 2D object placement, but object repositories are
required not only for Cassini and Titan, but also for
objects that serve to model the dynamic attributes
of other objects (i.e., the Parthenon). Another eco-
nomical aspect centers on the issue of computational
speed for these models. Would creating a simula-
tion in a more typical computer language would be
more efficient? The structure of objects and their
models within a VRML scene can be translated or
compiled into native machine code as easily as source
code; the 3D model structure becomes the -.....
code;" What is the advantage? If we consider psy-
chological factors, the 3D metaphor has significant
advantages. First, 3D spatially-specific areas serve
to improve our memory of the models (i.e., mnemon-
ics). Second, graphical user interfaces (GUIs) have
shown that a human's interaction with the computer
is dramatically improved when the right metaphors
are made available. Rube provides the environment
for building metaphors. One should always be wary
of mixed metaphors. We leave the ultimate decision
to the user group as to which metaphors are effec-
tive. A Darwinian-style of evolution will likely de-
termine which metaphors are useful and which are
not. Aesthetics plays an important role here as well.
If a modeler uses aesthetically appealing models and

metaphors, the modeler will enjoy the work. It is a
misconception to imagine that only the general pop-
ulous will benefit from fully interactive 3D models.
The engineers and scientist need this sort of immer-
sion as well so that they can understand better what
they are doing, and so that collaboration is made
possible; Is this art or science? The role of the Fine
Arts in science needs strengthening. With fully im-
mersive models, we find that we are in need of work-
ers with hybrid engineering/art backgrounds. It is
no longer sufficient to always think "in the abstract"
about modeling. Effective modeling requires mean-
ingful human interaction with 3D objects. So far,
the thin veneer of a scale model has made its way
into our engineering practices, but when the skin
is peeled back, we find highly abstract codes and
text. If the internals are to be made comprehensi-
ble (by anyone, most importantly the engineer), they
must be surfaced into 3D using the powerful capabil-
ities of metaphors (Lakoff and Johnson 1980; Lakoff
1987). This doesn't mean that we will not have a
low level code-base. Two-dimensional metaphors and
code constructs can be mixed within the 3D worlds,
just as we find them in our everyday environments
with the embedding of signs. At the University of
Florida, we have started a Digital Arts and Sciences
Program with the aim to produce engineers with a
more integrated background. This background will
help in the production of new workers with creative
modeling backgrounds.


It is sometimes difficult to differentiate models used
for the creation of pieces of art from those used with
scientific purposes in mind. Models used for science
are predicated on the notion that the modeling re-
lation is unambiguously specified and made openly
available to other scientists. Modeling communi-
ties generally form and evolve while stressing their
metaphors. In a very general sense, natural languages
have a similar evolution. The purpose of art, on
the other hand, is to permit some ambiguity with
the hopes of causing the viewer or listener to reflect
upon the modeled world. Some of the components
in worlds such as Fig. 1 could be considered non-
essential modeling elements that serve to confuse the
scientist. However, these elements may contribute to
a more pleasing immersive environment. Should they
be removed or should we add additional elements to
please the eye of the beholder? In Rube, we have the
freedom to go in both directions, and it isn't clear
which inclusions or eliminations are appropriate since
it is entirely up to the modeler or a larger modeling

community. One can build an entirely two dimen-
sional world on a blackboard using box and text ob-
jects, although this would not be in the spirit of cre-
ating immersive worlds that allow perusal of objects
and their models.
It may be that a select number of modelers may
find the TeaWorld room exciting and pleasing, and so
is this pleasure counterproductive to the scientist or
should the scientist be concerned only with the bare
essentials necessary for unambiguous representation
and communication? Visual models do not repre-
sent syntactic sugar (a term common in the Com-
puter Science community). Instead, these models
and their metaphors are essential for human under-
standing and comprehension. If this comprehension
is complemented with a feeling of excitement about
modeling, this can only be for the better. Taken to
the extreme, a purely artistic piece may be one that
is so couched in metaphor that the roles played by
objects isn't clear. We can, therefore, imagine a kind
of continuum from a completely unambiguous repre-
sentation and one where the roles are not published.
Between these two extremes, there is a lot of breath-
ing space. Science can be seen as a form of consen-
sual art where everyone tells each other what one
object means. Agreement ensues within a commu-
nity and then there is a mass convergence towards
one metaphor in favor of another.
We are not proposing a modification to the
VRML standard although we have found that poor
authoring support currently exists in VRML editors
for PROTO node creation and editing. We are sug-
gesting a different and more more general mindset
for VMRL-that it be used not only for representing
the shape of objects, but all modeling information
about objects. VRML should be about the complete
digital object representation and not only the repre-
sentation of geometry with low-level script behaviors
to support animation. Fortunately, VRML contains
an adequate number of features that makes this new
mindset possible even though it may not be practiced
on a wide scale. While a VRML file serves as the dig-
ital object, a model compiler is also required for the
proper interpretation of VRML objects as models.


There is no unified modeling methodology, nor should
there be one. Instead, modelers should be free to
use and construct their own worlds that have spe-
cial meaning to an individual or group. With Rube,
we hope to foster that creativity without limiting a
user to one or more specific metaphors. Rube has a

strong tie to the World Wide Web (WWW). The web
has introduced a remarkable transformation in every
area of business, industry, science and engineering.
It offers a way of sharing and presenting multimedia
information to a world-wide set of interactive partic-
ipants. Therefore any technology tied to the web's
development is likely to change modeling and sim-
ulation. The tremendous interest in Java for doing
simulation has taken a firm hold within the simula-
tion field. Apart from being a good programming
language, its future is intrinsically bound to the cod-
ing and interaction within a browser. VRML, and its
X3D successor, represent the future of 3D immersive
environments on the web. We feel that by building a
modeling environment in VRML and by couching this
environment within standard VRML content, that
we will create a "trojan horse" for simulation mod-
eling that allows modelers to create, share and reuse
VRML files.
Our modeling approach takes a substantial de-
parture from existing approaches in that the mod-
eling environment and the object environment are
merged seamlessly into a single environment. There
isn't a difference between a circle and a house, or a
sphere and a teapot. Furthermore, objects can take
on any role, liberating the modeler to choose what-
ever metaphor that can be agreed upon by a certain
community. There is no single syntax or structure
for modeling. Modeling is both an art and a science;
the realization that all objects can play roles takes
us back to childhood. We are building Rube in the
hope that by making all objects virtual that we can
return to free-form modeling of every kind. Modeling
in 3D can be cumbersome and can take considerable
patience due to the inherent user-interface problems
when working in 3D using a 2D screen interface. A
short term solution to this problem is to develop a
model package that is geared specifically to using one
or more metaphors, making the insertion of, say, the
Parthenon complex rooms a drag and drop operation.
Currently, a general purpose modeling package must
be used carefully position all objects in their respec-
tive locations. A longer term solution can be found
in the community of virtual interfaces. A good im-
mersive interface will make 3D object positioning and
connections a much easier task than it is today.
We will continue our research by adding to Rube
and extending it to be robust. In particular, we
plan on looking more closely into the problem of tak-
ing legacy code and making it available within the
VRML model. This is probably best accomplished
through TCP/IP and a network approach where the
Java/Javascript communicates to the legacy code as
a separate entity. We plan on extending the VRML

parser, currently used to create the model browser,
so that it can parse a 3D scene and generate the
Java required for the VRML file to execute its simula-
tion. Presently, the user must create all Script nodes.
The model browser will be extended to permit vari-
ous modes of locating models within objects. A "fly
through" mode will take a VRML file, with all object
and model prototypes, and place the models physi-
cally inside each object that it references. This new
generated VRML file is then browsed in the usual
fashion. Multiple scenes can be automatically gener-


I would like to thank the students on the Rube
Project: Robert Cubert, Andrew Reddish, and John
Hopkins. I would like to thank the following agencies
that have contributed towards our study of model-
ing and simulation: (1) Jet Propulsion Laboratory
under contract 961427 An Assessment and Design
Recommendation for Object-Oriented Physical Sys-
tem Modeling at JPL (John Peterson, Stephen Wall
and Bill McLaughlin); (2) Rome Laboratory, Griffiss
Air Force Base under contract F30602-98-C-0269 A
Web-Based Model Repository for Reusing and Shar-
ing Physical Object Components (Al Sisti and Steve
Farr); and (3) Department of the Interior under grant
14-45-0009-1544-154 Modeling Approaches & Empir-
ical Studies Supporting ATLSS for the Everglades
(Don DeAngelis and Ronnie Best). We are grateful
for their continued financial support.


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PAUL FISHWICK is Professor of Computer and
Information Science and Engineering at the Univer-
sity of Florida. He received the PhD in Computer and
Information Science from the University of Pennsyl-
vania in 1986. His research interests are in computer
simulation, modeling, and animation, and he is a Fel-
low of the Society for Computer Simulation (SCS).
Dr. Fishwick will serve as General Chair for WSCOO
in Orlando, Florida. He has authored one textbook,
co-edited three books and published over 100 techni-
cal papers.

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