Re: what does ADA stand for
At the beggining of Z.O.E 2 she introduces herself as "Advanced Backup Battle Unit ADA" which makes me suspect ADA is just her model name or handle.
I actually assumed it was a joke. She seems to be named after
the programming language. That or her name is a play on Ada Lovelace.
The latter makes a bit more sense considering the AI's personality is female and Lovelace's work laid the foundation for computer programming as we know it. Well...That and Kojima has that weird sort of humour.
[edit] Typo in the URL -_-' [/edit]