Value Mapping via UDF

Hi Gurus,

I have a standard mapping wit a udf which is calling value mapping in ID part i am not sure what inputs i need to pass to this UDF to get me the value .

XIVMService.executeMapping(src,dst,value);

now i have checked the SAP help and it tells src and dst are identifiers and value is the input .

So can somebody help me how what does the src and dst identifiers mean and how do i need to setup my value mapping in ID for this.

Thanks.

Kiran