I was reading a post which implied that some files could be stored client-side to speed things up.

I assume this is with the seperation model... Could someone please describe how this would work if I made a solution with 3 files (Data, Logic, GUI)?

Would a user basically be able to store Logic and GUI on their system, and then upon opening these - somehow access the data file remotely through the host?

Would anything change if the host is off-site (WAN)?

Sure, this would work fine. Just have your local files' file references to the Data file refer to the Data file that resides on the host. Having the Data file refer back to the Interface or Logic file is a little trickier, requiring a specific path on the client hard drive where those files reside.

what exactly is the "logic" part?