AS is DA/SA. It has a decocker. Decocking sets the trigger pull to DA, like the decocker on a HK, Sig, CZ.
QA has a decocker - smaller one than AS model, I think. Its decocker is pretty much useless IMO: once the gun is decocked, it cannot be cocked via trigger - you have to pull the slide back a little.
P.S.: The QA has a Glockish trigger setup - partially precocked striker.
DAO models: don't think they have a decocker.