Oh interesting so ITA is really just a retail front-end for TPF then? I guess I was misinformed about it as well.
The customers shop using ITA. The ITA shopping engine gets schedules, inventory and updates inventory from/to the backend (often TPF).
The shopping engine itself isn't trivial. ITA has the best shopping engine available.
I was under the impression that ITA used exclusively Common Lisp to inplement their software. I could be wrong, though.
ITA did build the full thing, but only Cape Air used it. The "full thing" being shopping, schedules, inventory, booking, cancel, change, check-in, etc.