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Title: Toward a convergence of systems and software engineering
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Title: Toward a convergence of systems and software engineering
Series Title: Department of Computer and Information Science and Engineering Technical Reports
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Language: English
Creator: Fishwick, Paul A.
Publisher: Department of Computer and Information Science and Engineering, University of Florida
Place of Publication: Gainesville, Fla.
Copyright Date: 1996
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Toward a Convergence of Systems and Software Engineering

Paul A. Fi-h', -i.
Computer & Information Science and Engineering Department
University of Florida


Recent trends in software engineering, especially within the object-oriented community, re-
flect a clear trend toward systems engineering methods. Object oriented designs, meant for
programming design, often take on the distinct appearance of system models of physical
networks and devices. It is not immediately apparent how the areas of "iii.i,,i lin,. and
pi' i.-i iii iii" 1 relate to one another, and why the convergence is taking place. To explore
the convergence in depth, we discuss common concepts between models and programs, and
discuss future trends in computer science which are forging a steady convergence between
models and programs. Ti, convergence is spawned by increased emphasis on object ori-
ented design, distributed systems, complex systems, new forms of analog computation, and
abstraction methodology. We close with a discussion of '.1 OOSE, which provides a compre-
hensive modeling environment for both programmers and modelers.

1 Introduction

Scientists and engineers use mathematical models frequently to avoid having to revisit the
drawing board whenever new designs are planned or a physical device is to be constructed.
.Ildels are patterns of behavior and structure in physical systems. By creating a model of
a system, a scientist is able economically record and abstract the behavior and geometry of
a physical system at various abstraction levels. While the use of modeling has been utilized
in software [42, 9, 13] and systems engineering [49], modeling requires a stronger base in
software engineering. Our purpose is to relate the use of model to program and to justify
the need for increased attention to modeling in software systems. We achieve this goal by
discussing the relationship between models and programs. Ti, effort of tying models and
programs closer together has been studied by a number of researchers. In the simulation
community, :'..ii Balci and Overstreet [35, 5, 39] have focused their modeling studies in
the bridge area of software engineering and simulation modeling. Oren [38], Zeigler [57, 58],
Cellier [12] and Fi-hli- i 1: [16] espouse modeling methods and formalisms which can be cross-
referenced in either simulation or computer science-based systems. Let's consider a simple
dynamic model where Fig. 1 illustrates a manufacturing floor where parts are provided to
a spiral accumulator and then fed through two workstation cells which machine parts by
performing lathe and drill operations. T111 raw stock arrives from the left via a central
conveyor. This type of application involves discrete parts flowing through a network of
resources which proceed when constraints are met. This -il-.-. --. the use of a Petri net to
model the system in Fig. 2.
T111 first figure is a conceptual model and the second is a dynamic model. Fig. 1 can be
considered a model which is non-executable, but descriptive of the overall topology of the
physical setup. T111 second model is executable and employs one of many possible dynamic

Cell 2


A Accumulator
R Robot
L =Lathe
D Drill

Figure 1: .1 illl ilii gl line with two robots and two machines.

AGV Running

Figure 2: Petri net for manufacturing line.

Cell 1

model types. We can see the potential use of these models in the construction of large
software and system parts. For instance, if we are constructing software to manage and
control the physical manufacturing devices, each of which will also have embedded digital
circuits, there is a need to abstract the system into a model to better understand the relation
between flowing parts and the reactive mechanical pieces.
.ddels can be constructed as visual or textual artifacts. Sample model types include
finite state and event automata, Petri nets, logic/production-rule systems, functional block
models, equation sets and spatial models [19]. ThI model serves as a mental device for
reasoning about the system without necessarily performing all experiments on the full system.
1, recover the model is generally cheaper to construct and maintain and serves as a pattern
used for archiving and disseminating system knowledge.
Given the importance of modeling, we find similar approaches in use throughout computer
science-especially within software engineering. Th, I is a convergence within software and
system engineering due to the strong ties between programming and modeling. By exploring
the nature of this convergence, we will strengthen the idea that system modeling is a useful
enterprise for software engineers and that software engineering trends-particularly in object
oriented design-are beneficial to system engineers. We limit our discussion of models to
dynamic models even though the use of geometric models' plays an equally critical role in
systems design. Tih design of models involving time (i.e., dynamic models) forms the basis
of the study of computer simulation. It is in the field of computer simulation that many of
the converging properties of systems and software engineering are found.
Our presentation will be as follows. First, we will discuss the positive impact of object
oriented design on program development and discuss limitations of object oriented design and
where improvements can be made. Subsequently, we explore the interrelationship of modeling
and programming. We attempt to answer the question of "How is a model different from a
program?" We proceed to a new model taxonomy for systems design and engineering using
several principles of computer programming languages. '.IOOSE ('.lii! iinl dealing Object
Oriented Simulation Environment) reflects our prototype implementation of the available
modeling types. We close the article with recommendations on how computer scientists can
play a more significant role in the design and representation of models.

2 Object Oriented Design

In object oriented (00) design, there is a natural focus on the classification of objects. Ob-
jects are created as instances of classes, classes are joined together in a tree-like fashion to
form class hierarchies, and classes are subsequently endowed with attributes and methods.
TIl, implementation of Simula[7] (an early simulation language which is still thriving, espe-
cially in Europe) is considered the first language which fully exploited the benefits of 00
programming. Benefits, often touted in 00 circles, include code reuse through inheritance
and polymorphism; however, the most important aspect of 00 design and implementation
is that 00 design embodies a fundamental principle: think in terms of the real world appli-
cation first: physical objects, attributes and methods. Thi,, is, if we are building a system
1Geometric modeling approaches find coverage in areas such as computer graphics, computer aided design
and computational geometry.

involving air traffic control, then we should build our program using physical objects: air-
craft, control tower, computer consoles. It could be argued that, while a focus on real world
objects is perfect for simulation applications, software applications present a different story.
However, given this issue, consider a sample of recent literature on software design using 00
principles [8, 10, 47, 51, 52]. This 00 emphasis is on models of physical systems such as
AT'. I machines and air conditioning control, and elicits the following question: "Are software
engineers doing system engineering?" Tli, 00 designs described are of physical systems. To
more fully appreciate why software engineering is orienting itself more toward modeling, we
need to define some terms:

Software Engineering: the process of creating software and specifications from concept
to executable software (in the form of a program), and continuing to analysis and
maintenance of the software.

Systems Engineering: the process of creating models and specifications for physical

Dynamic Model: a structure which serves to abstract the behavior of a physical system.

Geometric Model: a structure which serves to abstract the geometric configuration of
a physical system.

Program: an implemented algorithm which executes on a computer of some sort (analog
or digital).

Computer: a physical device capable of taking a program and executing it to produce
output. In our terminology,' iill ii, i is a very general concept and could refer to
the Babbage differential analyzer, a computer created from tinkertoys [14] or a modern
digital computer.

Sometimes, the terms i ,ili!" and "pi ,l .I,1" are used interchangeably. In a formal
sense, models and programs can be interpreted as equivalent, but the terms are quite over-
loaded and so we will need to examine them more carefully. To better explore the reasons
why there is a trend in integrating modeling, software and systems engineering, we need to
dig a little deeper in the following sections.

3 Model + Computability = Program: From Models to Programs

Computer programs are models which exhibit a high level of computability and control. This
statement requires some discussion and justification since the reader may ask "What physical
process, if anything, is the average computer program modeling?" Programs that execute
on computers model the physical attributes and devices of which computer is constructed.
For instance, when a digital electronic computer is used to execute a program which sorts
database records using an index field, this program causes transistors to switch and media
to become magnetized or scanned. This complicated sequence of physical transformations
represents the system hardware being modeled. Ti,1 main reason why we might not think of
the sorting program as a model of electromagnetic behavior is that we have so much control

over the system that we have essentially forgotten the physical substrate completely. Ti1
physical processes occurring while the program is executing have been "abstracted away."
For all we care, the underlying machine could be made up microscopic animals. As long
as we get consistent and timely output from the program, we will be satisfied that our
programming time is wisely spent.
We begin to think of programs as models when the level of control is relaxed and there
are uncertain elements injected into the physical system. Consider three scenarios in Fig. 3.
Ti, -, scenarios are based on ii liI! ml-" which are provided to illustrate the previous
point about models and programs. Fig. 3(a) displays the current state of a small ant colony.
Ti, ants may be foraging for food among obstacles or using a pheromone trail laid down by
ants who have located the food. We can build a model for this physical system using several
methods. One approach would be to assign individual behaviors to each ant, allowing the
ant to turn and move according to sampled random distributions. Ants move around or over
obstacles they find in their way. This physical system might not make a good computer on
which to run a program since (1) the dynamics of the ant colony does not exhibit Turing
equivalence [31], but more generally, (2) we are not in sufficient control of the ants. When we
say i ill rol," we are referring to a combination of the system property controllability [27]
and the concept effective procedure [2] which embody what we normally think of with a
modern pi 1.- 1111 "
Suppose now, that we change the ants so that they always move in a two-dimensional,
random fashion (random walk) and that we now have the ability to move or stop an an ant
at our discretion. Fig. 3(b) displays this situation after we originally cluster the ants in a
solid circle and then let them walk for a given time. We have removed the obstacles for a
more controllable situation and to achieve some level of regularity. TIl, ants now perform a
useful calculation called diffusion. Using the ants in this way, we may now model heat flow
on a two-dimensional metallic plate with an initial circular boundary heat source. This is a
tremendous capability, computationally, since many thermodynamic calculations may take
place with the ability to model a wide variety of physical phenomena, including diffusion-
limited ;.-.-.-i -.iii and reaction-diffusion properties. We are now in more control of the
ants than before with the scenario in Fig. 3(a), and we have created another model this
time, not of the ant behavior alone, but of the behavior of heat flow. At this point, we
could certainly claim that we are "pros_,iiiiI iii,; instead of just "iii,,li li,;" because of the
regularity associated with the ant behavior. Fig. 3(c) displays a situation where we are in
even further control of the ant motion. Ants are in one of two possible states: up or down.
Ants now occupy grid points and can be moved from one point to another arbitrarily through
an electrical signal issued to the ant via grid voltages. This final ant scenario provides a
cellular automaton (CA)-type of capability. Ti, ants are in one of two states: up (1) or
down (0), so we achieve a binary encoding. A partially bounded 2D CA can be shown to
have Turing equivalence since it can be divided into a finite number of 1D CAs [53], thereby
making the ants as computationally powerful as the modern general purpose computer. With
this new level of control and computability, we can program the ants to behave as we prefer.
T111 movement from Fig. 3(a) to Fig. 3(c) can be seen in either direction: gradually gaining
ant control or losing control. Ashby [3] refers to the loss or gain in regulation (control) of a
system as a change in requisite variety. Although this discussion provides us with one way of
better relating models with programs, we should note that programming has branched out

(c) Ant computer with
(a) Ants in a natural (b) Ants performing random Turn equivalence
environment walk (distributed control) (global control)
(no controls)

Figure 3: Ant models and programs

to the point where programs created using adaptive complex system models, such as genetic
programs and neural network programs, have blurred the distinction further between model
and program. With a more de-centralized type of control, we could program ants to achieve
key p1i" ,l .iii iii" results through mutation, gene selection and fitness functions. However,
we still would need to be able to exert control on individual ant behaviors even if the collective
orchestration of ant behavior is not performed. Analog computation enjoys a much richer
history than digital computing and also serves to make the idea of model and program
one and the same. Electronic analog computers [4] were constructed to solve differential
equations much like Babbage's engine was built to solve polynomials through differencing.
Tih programs for these computers are models in every sense since the program was built
to model physical phenomena. Recent work in analog computing falls into the category of
analog VLSI computation [33] where programs are constructed to manipulate the parameters
for neural networks, which perform a useful function, such as emulating biological sensors,
when executed. '. i ly other analog computations are possible [14] including those associated
with DNA-based computing [1].

4 Program + Metaphor = Model: From Programs to Models

Now, that we can claim that any program is a model of the underlying physical structure
of the computer, let's consider the conversion of algorithms or programs to models through
the liberal use of metaphor. Programs which code models of systems do not really require
a metaphor because they already have a direct connection to the real world. For instance,
if I write an event scheduling program which codes the actions of a program to simulate
a line forming at a grocery store cashier counter, then my program is a model. ThI.ii is,
it is something that requires interpretation or compilation and is subsequently executed.
However, if we have a program which sorts N numbers, how can this be considered a model2?
'.ily sorting and searching operations have analogs in the physical world. For instance, if
our sorting program does MergeSort then, our program can be seen as a model for customers
21-_. I,.i- for the moment, the general method pointed out in the previous section, where we were
modeling the '1,! -1 i1 computer elements.


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6 6 Q ~ ;f~ ~ 9;1~ ~

who are in two queues originally, but are then told they must form a single line due to
a malfunctioning cashier's machine. Plates stored in cafeteria spring-loaded compartments
are metaphorical equivalents of stack-based program and data structures. :' -inl 1i 1-. other
instances exist where-if we take a program and apply metaphor-we change the meaning
of the program to be one involving real world semantics.

5 Reasons for the Model = Program Convergence

Programs and models were not always distant cousins; they grew up together. Prior to the
advent of digital computers, most computers were modulated (controlled) by programs which
we think of as models today. Ti, electronic analog computer contained patch panel pro-
grams which we classify as constraint models in the form of differential equations. Programs
were constructed physically by patching together processing elements via coated wires on
perforated boards. Areas such as automata theory and cybernetics [3] paid special attention
to the relations of model to program. Today, a program is generally considered to be a tool
with a certain degree of freedom. CI ~i.l-l;y's hierarchy of language complexity-which can
be shown equivalent to levels of computational complexity-provides us with the power we
normally associate with programs. Generally, a modern program is considered to have the
power and expression of a Turing machine.
We have discussed how models and programs are very much like each other, sometimes
after the application of attributes such as control, computability and metaphor. But why
should the modeling4programming connection arise at this particular point in the history
of computer science? One reason is that we are becoming more liberal about how we define
-pi "'.;! ii' Also, the concepts of programs and hardware are merging. Some of the areas
accelerating this convergence of i.i I,, 1 as pi, ., i." are:

Modern Al',j Computation: Computation started originally on analog computers
and then later proceeded to digital computers. What was wrong with the programs
on the analog computers? One problem was (and still is) that fairly large scale analog
components have varying operating regions which affect the computation, say, of a
differential equation, even though the actual computation may be blindingly fast. TI1,
old patch panel method of programming has given way to better user interfaces with
computers which have higher degrees of reliability. Ti, analog VLSI approaches now
being used [33] are more reliable than the operational amplifiers used on the original
analog systems.

Distributed Computation: With a mainframe system, a program runs on a single central
processing unit (CPU). Now that systems are becoming increasingly distributed, we
are finding that computing elements are literally in every physical system, including car
engines, traffic lights, keyless entry systems, and even doors. "'- r.oponte, in his recent
book [36], expounds upon this trend from a computer-human interface perspective.
Distributed hardware implies that software must be distributed as well. As the single
program (once run on a single CPU) is gradually divided into its disparate elements,
each associated with a physical device, the programs take on the appearance of physical
models of the distributed system.

Emergent Programs: Ti, idea of evolving a program to solve a particular problem
is quite different from the usual software engineering approach of doing requirements
analysis and then writing a specification. Programs can be looked at like models with
embedded control so that if we want to build a program to solve problem X, we use
an optimization approach (in conjunction with genetic algorithms [22, 29] or neural
networks) to "evolx the program. Tli, program becomes a model of biologically
evolutionary behavior. Tli, work in artificial life [30] capitalizes on these modeling

6 Computer Scientists as Model Builders

Tli, overlaps between modeling and programming -ilu..-f that computer scientists take
a pro-active role in learning and applying the technique of modeling. An 00 taxonomy
containing only one kind of dynamic model (finite state machine) is limited, and so this will
require expansion to include several types of models (see Sec. 8), many of which include both
discrete as well as continuous system properties. Here is a list of -i-L-.. -1i 1 key focus areas
to facilitate a concentration in model building:

1. Software/Systems Engineering: Tli, convergence of models with programs means that
there is a corresponding convergence between software and systems engineering prin-
ciples. Hardware and software are integral system components and both need to be
modeled under a unified theme of system modeling. Tli, common formal base of all
systems is systems theory [6, 40], which leads to systems science [21] and engineer-
ing [49].

2. Object-Oriented Design: Ti, 00 philosophy promotes a clean interface between real
world objects and computer programs, and this is one of the key reasons why the 00
paradigm is successful. One thing we need to stress: perform an object oriented design
before thinking of implementation issues such as what particular language features
are to be exploited. Sometimes, the teaching of C++, for instance, is thought of
as equivalent to object oriented design. Instead, we need to teach design first, and
program later. One of the best ways to do this is to encourage the liberal use of
modeling. By constructing models before looking at code properties, we develop the
right skills to model.

3. Curriculum Development: With an increasing use of computers by scientists and engi-
neers, other disciplines will look toward computer scientists for help in modeling as well
as assessing algorithmic needs such as reducing computational complexity and achiev-
ing parallelism. Tli, computer science curricula need updating to include a heavy
dose of modeling. Computer science curricula tend to stress discrete systems over
continuous ones to the point of ignoring real world phenomena. Courses should put
more stress on modeling, computer simulation and systems theory (a unified view of
systems). Ti, use of interdisciplinary approaches in solving systems problems should
be highly encouraged. A healthy trend toward this interdisciplinary view is taken in
computational science and engineering (CSE) [45]. '.ideling should be introduced in
core computer science classes.

7 Abstraction

'.idels come in all flavors, and most model types are adept at describing system dynamics
at some specific abstraction level. Differential equations would normally be used to model
low level physical phenomena, and would probably be the lowest level of abstraction for
most systems. Fiii;l state automata, on the other hand, would be used to represent higher
levels. Abstraction is used in programs as well with regard to data and program abstraction.
1, -reover, the topic of code translation can also be seen in light of abstraction levels. For
programs, we might build a compiler which translates C source into assembly language
instructions. For models, we may have a Petri net which translates into equation sets. Thl
ant system in Fig. 3 serves as a springboard for example translations involving programs and
models: (1) physical ants modeling diffusion; (2) a digital computer interpreting a computer
program which simulates virtual ants where the ants model diffusion; or (3) A C program
translated into assembly code which is executed on an ant computer. TI, 1 are an endless
number of transitive couplings in which models and programs are interweaved to form chains
of translation or abstraction. Abstract models usually take less time to execute than more
detailed models and they present a different kind of information. All physical phenomena
are models of themselves and all dynamics of those phenomena are simulations to the limit
of the actual system. It is not practical to use an actual system to simulate itself since we
do not reduce cost, whether cost is measured in monetary units or time. However, seeing
modeling in this light permits us to see how abstraction operates over multiple scales. Thl
parallels between modeling and programming abstractions leads to other questions such
as one involving input and output. A program can be input to another program, which
operates upon it and produces a program as output. This procedure is common to compilers
and interpreters but what about in modeling? Normally, models associate signals with both
input and output, but these signals are just attributes of physical objects (in the 00 sense)
which are being transported. Consider a machine which takes two pieces of plastic and a
spring and then assembles these objects into an assembled output object. Each physical
object has different dynamics. Thlii- models can take models as input and produce models
as output. Even when the dynamics of an object do not change, as when a customer object
passes through a cashier resource, objects and their encapsulated models are accepted as
input and sent along to the output.

8 Modeling

Programs and models have historical differences in that programs have tended to be non-
visual in nature. Ti, 1 are counter-examples to this trend, such as the work in visual
programming languages and recent 00 program visualizations [23, 13], but overall the field
of modeling has always focused heavily on visual formalisms. To a great extent, the topology
in models correlate to the distinct geometric structures in natural and artificial systems: we
construct icons where we see physical pieces in the real-world system. Just as the discipline of
software engineering has emerged to address this question for software, in general, modelers
also have a need to explore similar issues: how do we engineer models? While there are
many modeling techniques for systems and simulation, we are often in a quandary as to
which model technique to use, and under what conditions we should use it. Our approach

Pictorial Text Function Variable Space Entity

State Event Equational Graph

Figure 4: Taxonomy for modeling.

is depicted in Fig. 4. This taxonomy of modeling requires some justification before we
describe the model types. Ti, taxonomy was created by considering a large number of
existing modeling methods in science and engineering. Through induction and clustering,
we proceeded to form categories. Conceptual modeling has its roots in object oriented
design, artificial intelligence and data base management systems. Declarative, functional
and constraint modeling methods are very similar to formal programming language types
which have the same names (i.e., declarative semantics, functional languages, constraint
logic languages). Tli, spatial modeling type was gleaned mostly from physics, and the
multimodeling type was designed to include those hierarchical models found most often in
digital circuit design and in combined discrete-continuous simulation models.
We will briefly discuss the model types in Fig. 4. A more complete written treatment
is provided in [19]. Ti, 1 are five basic model types, and one complex model type which
includes abstraction levels, each composed of one of the basic types. Conceptual models
represent the first phase in any modeling endeavor. All static and dynamic knowledge about
the physical system must be encoded in some form which allows specification of interaction
without necessarily specifying the dynamics in quantitative terms. Semantic networks [56]
present one way of encoding conceptual semantics; however, we have chosen object-oriented
design networks [10, 47] which have more formal treatment. Tli, ultimate conceptual model
is one based on database technology, such as an object-oriented database, capturing all facets
of the physical system.
Declarative models permit dynamics to be encoded as state-to-state or event-to-event
transitions. Ti, idea behind declarative modeling is to focus on the structure of state
(or event) from one time period to the next, while de-emphasizing functions or constraints
which define the transition. '. Idels such as finite state automata [25], .i l;.,v models, event
graphs [50] and temporal logic models [34] fall into the declarative category. Declarative
models are state-based (FSAs), event-based (event graphs) or a hybrid (Petri nets [41]).
Functional models represent a directional flow of signal (discrete or continuous) among

transfer functions (boxes). When the system is seen as a set of boxes communicating with
messages or signals, the functional paradigm takes hold. A ,lii flow model" is a functional
model. Tih use of functional models is found in control engineering [37, 15] (with continuous
signals) as well as queuing networks for computer system model design [32]. Some functional
systems focus not so much on the functions, but more on the variables. Such models include
signal flow graphs, compartmental models [26], and Systems Dynamics [46].
TIi 1, are two types of constraint models: equational and graph-based. Constraint models
are models where a balance (or constraint) is at the heart of the model design. In such a
case, an equation is often the best characterization of the model since a directional approach
such as functional modeling is insufficient. Equational systems include difference models,
ordinary differential equations, and delay differential equations. Graphical models such as
bond graphs [11, 28] and electrical network graphs [44] are also constraint based.
If a system is spatially decomposed as for cellular automata [55, 54, 24], Ising systems,
PDE-based solutions or finite element models, then the system is being modeled using a
spatial modeling technique. Spatial models are used to model systems in great detail, where
individual pieces of physical phenomena are modeled by discretizing the geometry of the
system. Spatial models are I it;i -I .,I or -1.i' -based." Entity-based spatial models
focus on a fixed space where the entity dynamics are given whereas space-based focus on
how the space changes by convolving a template over the space at each time step. PDEs
are space-based where the template defines the integration method. L-Systems [43] are
entity-based since the dynamics are based on how the organism grows over a fixed space.
Large scale models [48] are built from one or more abstraction levels, each level being
designed using one of the aforementioned primitive model types. Til, lowest level of ab-
straction for a system will probably use a spatial model whereas the highest level may use a
declarative finite state machine. Intermediate levels will often use functional and constraint
techniques. '. ,dels which are composed of other models are termed multimodels [20, 16, 18].
By utilizing abstraction levels, we can switch levels during the simulation and use the ab-
straction most appropriate at that given time. This approach gives us multiple levels of
explanation and is computationally more efficient than simulating the system at one level.

9 MOOSE Implementation

We are developing a li!ll ii dealing Object Oriented Simulation Environment ('. OOSE) to
allow users to construct models interactively using many abstraction levels. Th, I are three
levels to .iOOSE: (1) Graphical User Interface (GUI); (2) Blocks Language; and the (3) Sim-
Pack simulation toolkit. Tii, GUI is developed using Tk/Tcl and serves to interface with the
user via three windows: experiment,modeling,scenario. It is possible to construct multimod-
els interactively. Thi models allow a heterogeneous model construction capability. TIl,
Blocks language is used as an intermediate .i--i i:,l!; i,..i o" and SimPack [17] serves
as the base simulation library toolkit which executes all Blocks models. SimPack currently
has over 180 users worldwide and is documented in http://www.cis.uf
under "SimPack Simulation Toolkit." Other simulation information on '.iOOSE is located
at this URL as well. Til, current status of the '-.OOSE project is that all three major com-
ponents are working for single-level functional block models. We are currently implementing
the multimodeling capability.

10 Summary

Programming will be aided by model-based approaches, such as dynamic modeling, to help
software engineers construct large systems. We have examined the converging fields of mod-
eling and programming to illustrate the need for more attention to this growing area of
intersection. Software and systems engineers will work closely together using the same mod-
eling techniques, but perhaps at different abstraction levels. All levels are connected together
to form a multi-level large-scale model (a multimodel). In this synergistic systems view of
the world, models can be abstracted and refined to the limit where they are equivalent to
programs. This convergence has been accelerated by several factors including distributed
computation and real-time systems, object-oriented design methodology, complex system
modeling, evolutionary computing and abstraction methodology. Since modeling-during
the next century-will likely take up a significant percentage of all computer time, computer
science curricula must respond to the challenge by instrumenting courses in modeling and
systems study. As a stepping stone toward the objective of using a multimodeling construc-
tion tool, we have begun development on the '.IOOSE system.


I would like to acknowledge the following funding sources which have contributed towards our
study of modeling and implementation of the .1 OOSE system: (1) Rome Laboratory, Griffiss
Air Force Base, '.. York under contract F30602-95-C-0267 and grant F30602-95-1-0031;
(2) Department of the Interior under grant 14-45-0009-1544-154 and the (3) i:'N.,, i n, 1I Science
Foundation Engineering Research Center (ERC) in Particle Science and Technology at the
University of Florida (with Industrial Partners of the ERC) under grant EEC-94-02989.


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General Terms: Design, '.Iodeling, System
Additional Key Words and Phrases: Abstraction, Computation

About the Author:
PAUL A. FISHWICK is an associate professor in the Department of Computer and
Information Science and Engineering at the University of Florida. He received the B.S.
in '.1i11 11 iii from the Pennsylvania State University, ':.1 in Applied Science from the
College of William and l ry, and Ph.D. in Computer and Information Science from the Uni-
versity of Pennsylvania in 1986. He also has six years of industrial/government production
and research experience working at I,'' -lport :'I -, Shipbuilding and Dry Dock Co. (doing
CAD/CA '. 1 parts definition research) and at NASA Langley Research Center (studying engi-
neering data base models for structural engineering). His research interests are in computer
simulation modeling and analysis methods for complex systems. Dr. Fi-li" i 1: created the
comp.simulation newsgroup (Simulation Digest) in 1987 and moderated the group until
December 1993. He is a senior member of the IEEE and the Society for Computer Sim-
ulation. Dr. Fi-hl'i 1 was chairman of the IEEE Computer Society technical committee
on simulation (TCSIM) for two years (1988-1990) and he is on the editorial boards of sev-
eral journals including the ACM Transactions on Modeling and Computer Simulation, IEEE
Transactions on Systems, Man and Cybernetics, Tl,, Transactions of the Society for Com-
puter Simulation, International Journal of Computer Simulation, and the Journal of Systems

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