File Merging Problem

Hi,

I am Merging two files to one and sending to Receiver I am facing problems while Sender posting 4 files at a time how XI will take exact two files and merge?

Example:

their are 4 files in which abc_1.txt and abc_2.txt are one set and def_1.txt and def_2.txt are the other to merged .

If I post the above 4 files at a time then how can XI know to merge exact set of files to target?

Please Guid regarding this