Hi Nik,
You'll need at least two columns, one that contains the attribute values and another that contains the crosswalk value. You can then define the source system for this data in the mapping section of the dataloader tool.
When loading dummy data, I use this formula in google sheets to generate a simulated UUID that I use as a crosswalk value.
= DEC2HEX(RANDBETWEEN(0, 4294967295), 8) & "-" &
DEC2HEX(RANDBETWEEN(0, 65535), 4) & "-" &
DEC2HEX(RANDBETWEEN(0, 65535), 4) & "-" &
DEC2HEX(RANDBETWEEN(0, 65535), 4) & "-" &
DEC2HEX(RANDBETWEEN(0, 16777215), 6) &
DEC2HEX(RANDBETWEEN(0, 16777215), 6)
I hope this helps,
Roger
------------------------------
Roger Mukai
------------------------------