Data Transform:This rule can be created on the Data model category these are Used to 

1. To confirm one form of Data to another Form
2. To assign Default Values to the properties 
3. to copy one page to another page 
4. the default Data transform in PrPc in "pyDefault" and this can be called Under tab of process flow.

How to open the Data transform in Pega  in this follows.right click on Class Group after in this below