When you add a reusable transformation to a mapping, you add an instance of the transformation. The definition of the transformation still exists outside the mapping, while an instance of the transformation appears within the mapping.

Since the instance of a reusable transformation is a pointer to that transformation, when you change the transformation in the Transformation Developer, its instances reflect these changes. Instead of updating the same transformation in every mapping that uses it, you can update the reusable transformation once, and all instances of the transformation inherit the change. Note that instances do not inherit changes to property settings, only modifications to ports, expressions, and the name of the transformation.