Parametric 

Pro/ENGINEER Wildfire 3.0 models are driven using dimension values.  If a dimension of a feature is changed, that solid feature will update.  This change will then automatically propagate through the remaining features in the model, updating the entire part.

Parent/Child Relationships

Parent/Child relationships provide a powerful way to capture your "design intent" into a model.  Parent/Child relationships are naturally created between features during the modeling process.  When creating a feature, existing features that are referenced become parents to the new feature.  Also, if the parent features are updated, the child features will automatically update accordingly.

In the following figure, the PISTON model has a height of 18.5, with a hole dimensioned 8 from the top surface.  The height dimension is then modified to 24, and the model is Regenerated to update its features.  Notice that the parent/child relationship between the hole and the body of the model forces the hole to move upwards to maintain the 8 dimension.

Editing Height of the PISTON

This behavior (the hole referencing the top surface) is an example of the design intent that was built into this model.  Alternatively, the hole could have referenced the bottom surface, yielding a different effect when the model height is modified.