Definition

What is a Model?

A model is a representation of structure in a physical system and/or its properties. It describes (or specifies) four types of structure, each with internal and external components:

• systemic structure specifies
  • composition (internal parts of the system)
  • environment (external agents linked to the system)
  • connections (external and internal causal links)
• geometric structure specifies
  • position with respect to a reference frame (external geometry)
  • configuration (geometric relations among the parts)
• temporal structure specifies change in state variables (system properties)
  • descriptive models represent change by explicit functions of time
  • causal models specify change by differential equations with interaction laws
• interaction structure specifies interaction laws expressing interactions among causal links, usually as function of state variables