Hi Ruchi,
AFAIK - EDI does not have canonical data model. The structure is complex and it is hard to build canonical data model out of that. But if you observe the different version structure of same EDI type e.g. 850 V2, V3 or V4. The higher version is most of the time compatible with the lower version.
So if you create the mapping with V4 you can still derive some rule for lower version.
regards,
Harish