Debugging a mapping program

Hi Experts,

is it possible to analyze a specific UDF written in Graphical-Mapping program? like in abap we use F5,F6 and F7 for step by step analysis... (i.e what is the input entering into perticular field and at each step we can see what the value that is getting populated into each field)????

What is the difference between setting different trace levels in message mapping (in the test tab)... please tell me the exact difference..._please don't give the normal definitions of using trace levels_...