Custom

Select a Transformation Type of Custom only if you need a custom program AND it performs operations on data in such a way that it is not possible to track all data items in the source model that contributed to each data item in the target model.

Otherwise, even if you use a custom program, select the type of transformation it actually performs: join, union, pivot, or unpivot. The system then generates the code required for data lineage tracing. See How the system tracks data lineage.