The term double action or single action refers strictly to the function of the trigger. In a single action pistol or revolver, the trigger does nothing more than drop the hammer. In a double action pistol or revolver, the trigger both cocks and drops the hammer.
When referring to autoloading pistols, the DAO auto cannot be cocked and remain in a cocked state. Each squeeze of the trigger cocks the pistol and fires it. It cannot be carried in a cocked state. Hence, the trigger pull will remain constant at 6 lbs or 5 lbs or what ever. In a single action auto, the hammer must be cocked each time prior to shooting. The only thing the trigger does is drop the hammer. It can be cocked either manually or by firing a round and having the pistol cycle and cock the hammer. The trigger pull remains constant at 3lbs or 2 lbs or what ever.
DAO is Double Action Only like the S&W Sigma series. I think Glocks are DAO too but I'm not sure. Usually they have a really long trigger pull. After firing one you will be grateful for the 1911 trigger pull.