My client, he doesn't know what "FTP" is, and does not know how to upload his revised version of the current Excel calculation sheet which he designed, and is core-business, and coupled to an application form. He knows the ins and outs about Excel, from formulas to shortcuts, and i'm a total novice when he's explaining stuff to me.

I'm interfacing with his Excel sheet through PHP, and he does not have to change the way he works, and I don't. I don't need to know all the ins-and outs, I just need to know which cell needs what data, and the cells that are calculated and need to extract data from.

I'm now building a management backend for him in Rails, and it will work the same way. Maybe later those Excel calculations will be ported to the database, but for now there is no reason to bother my client with learning a new interface and changing the way he works.