A Constraint Property is a property that specifies the constraints of other properties in its containing Block. Every Constraint Property has composite AggregationKind and is typed by a Constraint Block. Constraint Properties are displayed in the constraints compartment on a Block shape. 

The Constraint Property shape containing information of its name, type and expression.

 To empower the constraint expression to perform calculations, you have to specify what system parameters should be consumed as variables of that constraint. You can define the Constraint expression as: