Physical Constraints

Definition

A physical constraint is a constraint that specifies a physical property of the application domain that cannot be violated.

Objectives

The typical objectives of a physical constraint are to:

• Ensure that the application or component conforms to all relevant:
  • Laws of Nature (e.g., laws of physics, chemistry).
  • Feasibility constraints due to physical reality of the application domain.

Examples

The following are typical examples of physical constraints:

• Laws of Nature:
  • “The speed of radio transmission is the speed of light (i.e., 300,000 km/sec).” (spacecraft control application)
  • “The temperature of the coolant cannot be less than absolute zero (i.e., -273° Celsius).” (superconducting partical accelerator management application)
• Feasibility:
  • “Delivery trucks can only move along along existing roadways.” (delivery application)
  • “Elevators cannot move between elevator shafts.” (elevator control application)
  • “Elevators cannot move from one floor to another floor without passing through all intermediate floors.”

Guidelines

The following guidelines have been found to be useful when producing physical constraints:

• Physical constraints are not required properties (i.e., requirements) desired by customer or user representatives.
• Physical constraints are natural properties that the application domain possesses regardless of the behavior of the application or component.
• Developers must use and respect the physical constraints of the application domain.
• Physical constraints are typically important in process control applications involving sensors and actuators.