Lets say I have a table name that exists in my database and I store it on a loca

Not through expressions no. Although if you're returning meta data such as table names you might as well store the cdt name in your database somewhere. I can't think of a practical way to use this though... you're the king of ill-fitting requirements! ;-) Your requirements sound like you're keeping much of the system logic in the database such as validations etc. I've done this before with Appian and ended up with a web service layer with all the intelligence and a very empty Appian solution - not a great fit.

Not through expressions no. Although if you're returning meta data such as table names you might as well store the cdt name in your database somewhere. I can't think of a practical way to use this though... you're the king of ill-fitting requirements! ;-) Your requirements sound like you're keeping much of the system logic in the database such as validations etc. I've done this before with Appian and ended up with a web service layer with all the intelligence and a very empty Appian solution - not a great fit.