Chapter2: System Studies
2-2:: A Corporate
Model::
SHAPE
Figure: Major segment of a corporate
model.
SHAPE 
Figure: The environment segment.
2-4:: Production
Segment::
SHAPE
Figure: The production segment.
2-5:: Management
Segment::
SHAPE
Figure: The management segment.
2-6:: The Full Corporate
Model::
|
SHAPE
Figure: The full corporate model.
2-7:: Types of System
Study::
Question: What is System
Engineering? (’99)
(OR)
Question: Differentiate
between ‘System Analysis’ and ‘System Design;.
(OR)
Question: What type of
system study that can be performed to study a system? (’01)
Answer: Types of System Studies:
1. System Analysis
2. System Design
3. System Postulation
System Analysis: System analysis describes how an existing
system or a proposed system operates. The ideal situation would be that the
investigator is able to experiment with the system itself. But, actually he/she
construct a model of the system and investigate the behavior of the model. The
results obtained are interpreted in terms of system performance.
System Design: In system design studies, the object is
to produce a system that meets some specifications. Certain system parameters
or components can be selected or planned by the designer, and, conceptually, he
chooses a particular combination of components to construct a system. The
proposed system is modeled and its performance predicted from knowledge of the
model’s behavior. If the predicted performance compares favorably with the
desired performance the design is accepted. Otherwise, the system is redesigned
and the process repeated.
System Postulation: System postulation is characteristics of
the way models are employed in social, economic, political and medical studies,
where the behavior of the system is known but the processed that produce the
behavior are not. Hypotheses are made on a likely set of entities and
activities that can explain the behavior. The study compares the response of
the model based on these hypotheses with the known behavior. A reasonably good
match naturally leads to the assumption that the structure of the model bears a
resemblance to the actual system, and allows a system structure to be
postulated.
System Engineering: System engineering describe system
studies where a combination of analysis and design is aimed at understanding,
first, how an existing system works and then preparing system modification to
change the system behavior.
q Question:
Illustrate system analysis study with an example. Which types of systems need
system postulations to study the system? (’01)
Answer:
1st
part: (2-8, page-28-30, System analysis)
2nd
part: Sometimes social, economic, political and medical studies need system
postulation to study the system where the behavior of the system is known but
the processes that produce the behavior are not.
2-9:: Examples of System Design::(N.B. Please follow Book Page-(31-34)
Three computers are being considered as possible system
components: a slow, a medium, and a fast computer, which have instruction
execution rates of 25,000, 50,000, and 100,000 instructions a second. In
addition, four buffer sizes are being considered: there could be a one-, two-,
five- or ten-character buffer.
SHAPE
Figure: An input-output system.
There are M messages coming into the computer and kM replies
going out every second. This requires that Mm + kMr characters pass through the
buffer every second. Since the buffer holds b characters, there will be M(m +
kr)/b interruptions second. Adding together the instructions needed to process
messages, prepare replies, and service buffer interruptions, the number of
instructions to be executed every second, denoted by N, is given by,
If we denoted the number of instructions per second that the
computer can execute by s, the condition to be met for the computer to keep up
with the data flow is that 
To simplify the discussion, suppose the details of the message
traffic are specified with the following values:
M = 5 m = 15
K = 0.1 r = 50
Only the buffer size, b, and the computer speed, s, remain to
be selected. Putting the given values into the formula for N, the condition,
after simplification, can be written
2-10:: System
Postulation::
Example
of system postulation:
Here we illustrate the use of system postulation by looking at
a study designed to investigate the function of the liver in the human body.
When a chemical, thyroxine, is injected into the blood stream, it is carried to
the liver. The liver can change thyroxine into iodine which is absorbed into
the bile. But the conversion and absorption not occur instantaneously. Some of
the thyroxine reenters the blood stream to be re-circulated and returned to the
liver. By using radioactive isotopes, it is possible to measure the rate at
which thyroxine is removed from the blood stream, but the precise mechanism by
which it is transformed from the blood to the liver and then to the bile was
not known.
In the study, a mathematical model was constructed assuming
that the body can be represented as three compartments and that the rates at
which thyroxine is transferred between the compartments are proportional to the
concentration of thyroxine in the compartments. Following figure-1 illustrates
the model and shows the assumed transfer coefficients between compartments. The
compartments 1, 2 and 3 represent the blood vessels, the liver, and the bile,
respectively. The model leads to three simple differential equations which are
shown, together with their general solutions in figure-1.
SHAPE
Figure-1: Mathematical model of the
liver.
Figure-2 shows the result of comparing actual measurements
against the model predictions for one set of assumed values of the
coefficients.
Figure-2: Results from model of the
liver. (page- 36)
It can be seen that the match between the results of the
theoretical model and the experiment is close, which suggests that the
hypothesis on transfer rates is reasonably accurate and allows estimates of the
transfer coefficients to be made.
The above types of models are called compartment models. They
are used extensively in medical, biological and ecological studies.
Question: Illustrate system analysis study
with an example. Which types of systems need system postulations to study the
system? (’01)
Answer:
1st
part: (2-8, page-28-30, System analysis)
2nd
part: Sometimes social, economic, political and medical studies need system
postulation to study the system where the behavior of the system is known but
the processes that produce the behavior are not.
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