A model is a description of a system (that is created to help understand the system)

• Physical Models:
  • Paper, clay, plastic, wood, metal, etc...
• Conceptual Models:
  • Mathematical, computational/numerical, diagrammatic/visual/graphical, textual, etc...

• Static:
  • Models of the aspects of the system that do not change (sometimes called structural)
• Dynamic:
  • Models of how the system changes over time (sometimes called behavioral)

• Some Observations:
  • Complex systems are hard to understand
  • Models can be used to make them easier to understand
• An Example:
  • You can probably build a doghouse without a model
  • A house would be very difficult to build without a model
  • A skyscraper would be impossible to build without a model

• A Common Problem:
  • Start with a doghouse
  • Keep adding on until you have a skyscraper
• What Models Provide:
  • An understanding of a system (as it is or should be)
  • A specification of a system
  • A template for construction
  • A record of the decisions that were made

• The same object/concept can be conceptualized at different levels of abstraction
• A system that is conceptualized at a particular level of abstraction can be modeled at different levels of abstraction

• Viewing a Car as a System:
  • Low Detail - A source of emissions
  • Medium Detail - A contributor to traffic congestion at an intersection
  • High Detail - A mechanical motive device
• Modeling a Car as a Source of Emissions
  • Low Detail - Relate the number of cars to total emissions
  • Medium Detail - Consider the number of miles and driven and the average drive cycle (e.g., EPA estimates)
  • High Detail - Consider car following behavior and engine performance