You can define transformation references, such as schema or mapplet references, by selecting a schema or mapplet to serve as a reference. Some Data Processor transformations require a hierarchical schema to define the input or output hierarchy for relevant components in the transformation. To use the schema in the transformation, you define a schema reference for the transformation. You can also use a specialized action named the RunMapplet action to call a mapplet from a Data Processor transformation. To call a mapplet, you must first define a mapplet reference for the transformation.