Environmental Systems
Reading Prompt: Systems and models
Selected text book chapters will provide some comprehensive information on the properties of models and systems.
After completing this reading prompt you should be familiar with the following key terms and concepts:
Texts you need for this reading prompt:
After completing this reading prompt you should be familiar with the following key terms and concepts:
- system
- system boundaries
- system components
- system structure
- system purpose
- (dynamic) model
Texts you need for this reading prompt:
Systems
The first text of this reading prompt describes fundamental principles of systems. Some guiding questions while reading would be:
Once you have read the chapter, summarize the aspects that seem most important to you in some kind of bullet point list. Have a look on the thoughts on systems below afterwards and compare them to your notes.
- Why is it important that systems have a purpose?
- What is system structure and what are its consequences?
- What happens to a system in terms of integrity if components are excluded?
- How can one describe the full state of a system at any time?
Once you have read the chapter, summarize the aspects that seem most important to you in some kind of bullet point list. Have a look on the thoughts on systems below afterwards and compare them to your notes.
Some thoughts on systems
Since this might be the first text you have read in the field of system dynamics, here is a short summary of some important aspects taken from the book chapter:
- Systems serve a special purpose.
- Systems have specific components and a specific structure.
- The integrity of systems is destroyed if a single component is removed.
- System changes result from influences of the surroundings, from the internal system composition or from a combination of both.
- A system has a surrounding environment.
- The environment has an influence on the system and the system has an influence on the surrounding.
- By definition, no feedback is possible between a system and its surroundings.
- The boundary between a system and its surroundings marks the “line” where interactions between components within the system are greater than interactions between components of the system and counterparts outside the system.
- The current state of a system is defined in full and at any time by the state variables (also known as “levels” or “stocks”).
- System levels (or stocks) are independent of each other.
- The dimension of a system equals the number of system levels.
- The state of the system levels is not inevitably represented by the behavioral pattern of the system (i. e. a red warning light on the refrigerator does not tell me the exact temperature inside the fridge).
- The behavior of a system can be affected by (time-dependent) boundary conditions and (constant or time-dependent) system parameters.
- System changes result from influences of the surroundings, from the internal system composition or from a combination of both.
Models
The second text of this reading prompt will focus on models. Some guiding questions while reading would be:
Once you have read the chapter, summarize the aspects that seem most important to you in some kind of bullet point list. Have a look on the thoughts on models below afterwards and compare them to your notes.
- What is a model?
- What does define a model?
- How can one estimate a model's validity?
Once you have read the chapter, summarize the aspects that seem most important to you in some kind of bullet point list. Have a look on the thoughts on models below afterwards and compare them to your notes.
Some thoughts on models
As above, here is a short summary of some important aspects taken from the book chapter:
Not in the text above but following Imboden & Koch (2008), one can state that model parameters
- Models are simplified representation of a real world system.
- The purpose of a model is always related to a specific problem.
- The purpose of a model defines the validity of the model which is always restricted.
- The purpose of a model and the simulation options should fit the user requirements i. e. the specific problem of the user.
- A model must be valid for a certain purpose i. e. the model and the real system must show the same behavior for this purpose.
- The structure of a opaque-/glass-box model must be in accordance with the structure and interactions of the real system.
- The output of a model must be within a reasonable range of the corresponding empiric results.
- It is worth mentioning that the above characteristics apply for all models but that does not mean that there is only one type of model.
Not in the text above but following Imboden & Koch (2008), one can state that model parameters
- can be retrieved from iterative simulations, from real world measurements or experiments,
- are independent of other system variables and can be constant or time-variant.