Constraint Models are a method of programming in which two or more values are bound together in a manner so that a change in one value is automatically relected by a corresponding change in the others. Such models are common in certain types of mathematical and scientific modelling, and are a key feature of the SpreadsheetModel.

A classic example of a simple constraint is the automatic conversion between two different units of measurement, e.g., degrees Fahrenheit and degrees Celsius. If the values are modelled as a constraint, then setting the value of one of the two - say, setting the Celsius value to 100 degrees - would AutoMagically cause the Fahrenheit value to be reset to 212 degrees, while changing the value of Fahrenheit to 98.6 degrees would cause the Celsius value to be reset to 37.0 degrees.
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ProgrammingParadigm