260 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
THOUGHT CRITERIA FOR USE OF SYSTEM DYNAMICS
Jiang Yong Ning
Institute of Electronics Industry
ABSTRACT
The purpose of this paper is to explore the thought cr-
iterie of modelling in system dynamics.
Thought criteria of system dynamics has appeared as a dy-
namic theory in the field of economics. This field has three
_ Characteristics: nowlinear fluctuation, time delay and qual-
itative transformation. These characteristics constitute the
basis of model building in system dynamics.
The concept of thought criteria is based on the process
ef cognition: Study of subject--Modelling--Understanding of
object. It is closely associated in series with interactive
elements of the system. The modelling has been inspected in
practice as a transitional link between subject and object so
that. modelling has turned into a cognitive and analytical
method: and@will be used, first, to carry out simulated tests
ot the prototype and thus deepen our comprehension of it;
secondly, to compare the specific properties of theoretical
‘and experimental systems with those of the real system, and
by means of the result from these comparisons, to improve a
causal relation loop; and thirdly, to. show a tendency to pass
from qualitative analysis to quantitative analysis, thus
leading to the combined assessment of the system. The rules
of the combined of the application of the system model are
identification, interchangeability, controllability and
aveéilability.
4, ENPRQDUCTION
System dynamics as a total system mathodology has been
received a great deal of attention in both the hard and soc-
ial sciences. System dynamics studies the laws of dynamic :
behavior of information-feedback systems. It uses computer
simulation to provide«some understanding and improve the ways
in which complex systems of human activity may be improved.
Modern natural science.came into being only after the
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emergence of experimental science. Now system dynamics has
constructed a bridge between the natural and the social sc-
iences.
The computer simulation method has played a relatively
important role in both sciences, and pushes forward a strong
knowledge flow between them. This has two results, one being
the use of achievements in natural scientific research to
overcome complex problems in national economy; the other is
the use of natural sciences to fulfill socio-economic demands.
Thought criteria of system ‘dynamics has appeared as a
dynamic theory in the field of economics. In the past three
decades the great successes achieved by system dynamics have
transformed social system model building into a scientific
means of understanding society clearly.
2, THE UNITY OF SYSTEM IN SYSTEM DYNAMICS MODEL
The degree of similarity between 2 model and its protot-
ype isinever complete. As model testing is carried on by the
system dynamics method, modelling in form is a concentrated
expression of the subjective, but in content, it is an obj-
ective law of activities of the objective, characteristics,
unity and coherence as well as relative reflection of the
true situation in the decision process.
Within our cognizance of the system elements, the unity
of system in system dynamics may be expressed in four aspects:
1). The studied system is an amalgamation of multiple
factors which condition each other. Its elements are in a
controllable position.
2). The characteristics of the relation between the var-
ious elements gives rise to the characteristics of the system
as a whole,
3). The factors which control the element's characteris-
tic also effect the behavior of a system.
4). The relation of each element in a system structure
is pluralistic, and causes the different kinds of system fun-
ection.
In the case of system unity, system dynamics models mir-
cor a dynamic trend in economic field. This field has three
tharacteristics: nonlinear fluctuation, time delay and
ba
262 THE 1987 INTERNATIONAL CONFERENCE OF THE SYSTEM DYNAMICS SOCITY. CHINA
qualitative transformation. These characteristics constitute
the basiés of model building in system dynami¢s as follows:
Field Characteristics Expressible Principle
1). Nonlinear fluctuation Behavior of a system
2). Time delay Dynamic input/output flow
= 5 diagram .
3). Qualitative transformation Cause-and-effect infor-
mation-feedback loop
As an organic whole this model testing includes obser-
vition, analysis and synthesis, induction and deduction, and
draws a correct conclusion from objective facts. Therefore,
system dynamics as a total system methodology has two parts,
program and analysis. The causal relation and interaction of
elements in practice are systematized by program; the analy-
sis is calculated in mathematical program by computer. Mean-
while they are judged by man's understanding.
System dynamics over many years has been applied to.a
wide-variety of situations with modern scientific theories in
practice suchas:
For System. Means and Ways
Deseription of system Quantification and Graphics
structure ‘
Feedback of information Cybernetics. and Information
flow theory
Construction of model- Mathematical statistics and
ling Analogy ;
Analysis of system behav- View the situation as a whole
ior . with Competition theory and
Decision science
3. STUDY OF SUBJECT__MODELLING__UNDSRSTANDING OF OBJECT
Modelling is an abstract means of studying objects. For
this step, knowledge and-social practice are not a goal in
themselves, but a means of reaching the stage of simplified
cognition and shortening the information flow process obtain-
ed from ‘social prototypes.
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This type of modelling simulates the properties of real
objects. The conception of thought criteria of system dy-
namics is based on the process of cognition: study of sub-
ject--modelling--understanding of object.
The control relation are present in the various natural
objects, such as in the technical organization, biological
system and social action. There are many factors, some of
which can be controlled, but some of which can't, so we need
to study specific types of relations. The object of study is
not merely certain, concrete elements, but a whole system.
While we probe the unity of complex society, the reflec-
tion of a direct judgment through the senses is not the ess-
ence of an object, but the characteristics of what is obser-
ved or indirectly perceived from objects. It arises from the
process: of recognition: Image--Problem--Idea, This idea exp-
resses the synthesis of the actions of society. This synth-
esis in turn dynamically affects the model.
Now we have:the means to handle complex problems by sy-
nthetic methods. A given factor existing ‘in one area of a
model may affect other areas. The factors and actions may
result in instability. System dynamics has been carefully
thought out to handle unstable situations, and it has relat-
ed the subject ( such as social individual, social group,
social levels ) and the object ( such as natural, social, and
industrial systems ) to each other in modelling, and reached
the goal of regulation and control of their interaction.
Modelling has been inspected in practice as-a transition-
al link between subject and object so that modelling has tur-
ned into a cognitive and analytical method and will be used,
first, to carry out simulated tests of the prototype and thus
deep our comprehension of it; secondly, to compare the spec-
ific propertiés of theoretical and experimental systems with
real systems, and by means of the result from these compar~
isons to improve a causal relation loop; and thirdly, to show
a tendency to pass from qualitative analysis to quantitative
analysis, thus leading to the combined assessment of the sy-
stem.
The qualitative analysis of system dynamics is that it
identifies the caugal relations in a structure of system, the
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positive roles among elements and the kinds of information
flow in input/output relations; and describes their cyclical
behavior, delay interaction and model validity; and delimits
the boundaries of the system, the frontiers of the closed
loop and causal-loops diagram; and recommends. the changes of
control policies.
The quantitative analysis of system dynamics is that-it
examines the selected structure of system, the results of the
_ decision process and the benefits of optimum control; and
provides policy choice for economic growth.
4, EWALUATION OF SYSTEM MODEL
Flow diagrams are essential to design the final quantif-
ied simulation model.
The rules of the combined assessment of the application
of the system model are identification, interchangeability,
controllability and availability.
It is considered that the evaluation of the system model
is very important. System model draws a clear distinction
between characteristics of each part in the system and makes
also clear the interaction of parameter changes thus provid-
ing level control with material flow.
5. CONCLUSION
The Thought Criteria for use of system dynamics is very
important, we can use it to acquire a better understanding
for building model of system dynamics.
REFERENCES
Forrester,J.¥. 1961, Industrial Dynamics (MIT PRESS)
Forrester,J.#. 1968, Principles of Systems (WIT PRESS)
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