Get the value of a particular field in a segment of an Idoc

Hi All,

I have a requirement where I need to write a report which will fetch the value of a particular field in a segment of an idoc.

I have the idoc number segment and field name as input parameters by which I can fetch Sdata from EDID4 but the confusion is how to find the exact field value from that Sdata. How to Map the SDATA to the segment structure.

Please advice...