Parametric models
Parametric models test whether you can capture engineering constraints and bind them to value properties so they can be evaluated. Expect questions on constraint blocks, constraint properties, parameters, binding connectors, and unit consistency.
Constraint blocks
A constraint block is a block with «constraint». Its parameters are properties of the block, and its body holds the equation, written in tool-specific text, OCL, or an expression language. Constraint blocks are definition elements: they are reusable and can be composed of nested constraints.
Constraint properties and binding
A constraint property is a usage of a constraint block inside another block or on a parametric diagram. Binding connectors join a parameter to a value property, or to another parameter, and assert equality. They are directionless: they do not carry data flow; the solver decides what to compute.
Value properties and units
Bind only to value properties typed by value types that carry dimension and unit. Mixing metres and feet, or kilograms and pounds, silently corrupts results; convert first or use the units library.
Trade studies
To compare alternatives, vary one or more value properties, re-evaluate the constraints, and compare the measures of effectiveness. The parametric model provides the computation; the trade study provides the decision framing.
Worked example
Constraint block OhmLaw has parameters V, I, R and body V = I * R. Inside block Circuit, constraint property ohm : OhmLaw is bound to value properties voltage, current and resistance. Supplying any two values lets a tool compute the third; inconsistent units produce a binding error rather than a number.
Traps
Confusing a parameter with a value property, drawing binding connectors with arrows and assuming data flow, confusing the constraint property with its defining constraint block, putting equations on a block definition diagram, and ignoring unit compatibility.