The hierarchy occurs in the following order:

Workflow parameters
    Mapping parameters
        Mapplet parameters
            Logical data objects
                Transformation/data object parameters

A parameter assigned to an object at a higher level in the hierarchy can replace parameters assigned to lower levels in the hierarchy. You can use the hierarchy to override parameters in the following ways:

Override parameters assigned to low-level objects in the hierarchy by assigning parameters to high-level objects in the hierarchy.
Bind low-level object parameters to high-level object parameters to use the default values of the high-level object parameters in the run-time mapping or workflow.

For example, you can add a reusable transformation to a mapping. To replace parameters in the reusable transformation, you can create mapping parameters to override the transformation parameters. Or, you can expose the transformation parameters as mapping parameters to bind the transformation parameters to mapping parameters. The transformation uses the default mapping parameter values at run time.