To me it doesn't seem like the rocket science you're making it out to be. Most teams store data in non-silly ways that correspond to the common reality that th

To me it doesn't seem like the rocket science you're making it out to be. Most teams store data in non-silly ways that correspond to the common reality that the data represent. For example everybody knows what a date of birth is, and that it has a day, month and year. If the year is missing from the source data, you set it null in your intermediary data model. If it's required in the destination data... basic solution would be choose a default and notify the user; deluxe solution would be to give them some choices up front what to do about it (since you'll already know about the mismatch based on knowing the source & destination providers). Max number of phone numbers: if the source contains more than the destination's max, stop at the max (basic) or display a list and ask the user to eliminate some (deluxe).