Hi Arvind Kucheria,
If you have a rule the secondary data source and copy the resutls to the main data source. It shouldn#%92t be too hard to implement using rules and xpath. Of course, you could just do it in code too.
1. Main data source field is non repeating field
You need to write On After Change event for secondary data source fields. In this function you need to get the secondary value and set this value to main data source field. When ever second value comes then you need differentiate for those values, before set this second value you need to append some thing like that spaces are any special characters between them.
2. Main data source field is repeating field
If you have main data source is also repeating then you need to create empty node for every secondary data source value and set the value for it before appending this node to main data source.