Chapter1: Introduction to System Analysis

Question 1

What are the basic three properties an object must have to be a system by definition? Which additional properties do dynamic systems have?

Answer 1

• Identity: A system shows a specific behavior or has a certain purpose.
• Structure: It is a set of objects with cause-effect relationships.
• Consistency: There are elements or relationships we can‘t take away without destroying or changing the system‘s identity.
Besides, the structure of dynamic systems contains feedbacks.

Question 2

In general, understanding dynamic systems is not self-evident for humans. Where do the difficulties come from? Could it be a problem? Why or why not?

Answer 2

• Our brain is not an instrument for understanding the world per se, it‘s an organ that should guide us more or less safely through life.
• When our mind evolved, understanding feedbacks was simply not necessary for survival.
• is necessary, to understand „reality“ and to act goal-orientated.
• is not a natural way of thinking for us.
• Must be trained. Models can be highly valuable for that.

Question 3

Does VENSIM find exact analytical solutions or does it approximate by numerical methods? Why?

Answer 3

Simulations …aren‘t models, but the numerical integration of a simulation model (after defining initial conditions and parameter values). Numerical Integration: Approximative Method (Runge-Kutta, Euler…), not an exact solution.
Such a simple solution (for relevant systems) exists in exceptional cases only. Mostly, the exact solution is hard to find or even nonexistent.

Question 4

Should a model contain all details of the real world? Why or why not?

Answer 4

The Purpose of a Model… determines the kind of model and the model structure (system borders, temporal, spatial, physical resolution). Models which describe a system in an appropriate way for any purpose don‘t exist. Analogy: Different types of maps.

Question 5

Why is the use of software tools like Vensim? Do they solve resource management problems automatically? Why or why not?

Answer 5

They translate the mathematical model of a problem into computer codes. No, they don’t solve automatically further interpretation of the results is needed.

Question 6

What are a model’s classifications ?

Answer 6

• statistic vs mechanistic
• continuous vs discrete
• deternministic vs stochastic

Question 7

Why do we use models ?

Answer 7

• Structuring Knowledge Depicting the information that is considered relevant for a problem in a coherent way. Identifying inconsistencies and knowledge gaps!
• Generating Knowledge Analysing system properties, which can‘t be derived from
observations and experiments alone.
• Management Assessing the effects of manipulations in a system, that can‘t be
tried in the real system due to ethical, technical, financial, logistical reasons or due to high risks.
• Prognosis Estimate future system behaviour.

Question 8

Which of the following items are systems, which not? Why?
Cannon Ball:
Computer:
City:
heap of sand:

Answer 8

Cannon Ball:
Identity: yes, a cannon ball has a certain purpose
Structure: no, there are no cause-effect relationships within a cannon ball
Consistency: yes, we cannot take away anything without changing the cannon ball in something else
 A cannonball is not a system because of the lack of structure
Computer:
Identity: yes, a computer behaves specific and has a certain purpose
Structure: yes, set of objects, that have cause-effect relationships
Consistency: yes, the computer and its functionality will be changed as soon as something is taken away
 Yes, a computer is a system
City:
Identity: yes, a city has a specific behavior and a certain purpose
Structure: yes, a city has different objects with cause-effect relationships
Consistency: yes, if something is changed or taken away, the identity of a city is affected
 Yes, a city is a system
heap of sand:
Identity: yes a heap of sand can have a specific purpose
Structure: no, a heap of sand contains only sand without cause-effects
Consistency: no, one can change or take away some parts of it and it will stay a heap of sand.
 A heap of sand is no system.

Question 9

Explain the term ‘feedback’

Answer 9

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop.The system can then be said to feed back into itself.

Question 10

Systems Analysis-Flowchart ?

Answer 10

Question ->
System Borders, State ->
Variables->
Analyse->
Relationships->
Verbal, graph. Model->
Mathematical Model->
Parameter Values->
Simulation Modell->
Initial Values->
Simulation: Experiments->
Interpretation